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Glucose and caffeine effects on sustained attention: An exploratory fMRI study.

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Abstract

Caffeine and glucose can have beneficial effects on cognitive performance. However, neural basis of these effects remain unknown. Our objective was to evaluate the effects of caffeine and glucose on sustained attention, using functional magnetic resonance imaging (fMRI). Forty young right-handed, healthy, low caffeine-consuming subjects participated in the study. In a double-blind, randomised design, subjects received one of the following beverages: vehicle (water, 150 ml); vehicle plus 75 g of glucose; vehicle plus 75 mg of caffeine; vehicle plus 75 g of glucose and 75 mg of caffeine. Participants underwent two scanning fMRI sessions (before and 30 min after of the administration of the beverage). A continuous performance test was used to assess sustained attention. Participants who received combined caffeine and glucose had similar performance to the others but had a decrease in activation in the bilateral parietal and left prefrontal cortex. Since these areas have been related to the sustained attention and working memory processes, results would suggest that combined caffeine and glucose could increase the efficiency of the attentional system. However, more studies using larger samples and different levels of caffeine and glucose are necessary to better understand the combined effects of both substances.

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... These include glucose, taurine, L-theanine, and ginseng (Table 1). 4,[10][11][12][13][14][15][16][17][18][19][20][21] Throughout this section, "interactive effects" of ingredients in combination with caffeine refers to effects that are quantitatively or qualitatively different than the effects of the substances administered alone. ...
... 22,23 Six studies 4,10-14 were identified that administered glucose and caffeine alone and in combination, allowing clear dissociation of the separate and interactive effects of the substances on mood and cognitive performance.With regard to mood, 2 studies reported mixed interactive effects of glucose and caffeine, 11,14 3 did not report any interactive effects, 4,10,12 and 1 did not assess mood. 13 In 1 study, 14 30 g of glucose counteracted caffeine (80 mg)-induced increases in hostility across cognitive testing, while in the other study, 11 50 g of glucose and 200 mg of caffeine administered together increased tension. 11 With respect to subjective energy, only Young and Benton 14 reported that 39 g of glucose counteracted short-term (30 min) increases in subjective energy as well as long-term (90-150 min) increases in tiredness after 80 mg of caffeine, while Giles et al. 11 found no evidence of interactive effects on fatigue. ...
... Interactive effects of glucose and caffeine on measures of attention were found in 3 of the 6 studies, 4,10,14 but not in the others. [11][12][13] Two studies reported that a combination of glucose (37.5 mg and 75 mg) and caffeine (75 mg) produced greater decreases in reaction time than either substance administered alone, 4,10 but another reported that 30 g of glucose attenuated caffeine (80 mg)induced decreases in choice reaction times at 90 min and 150 min. 14 The discrepancy between studies is likely due to the tasks used: interactive effects were observed in attention tasks with a higher level of demand 4,10 than simpler tasks. ...
Article
Sales of energy products have grown enormously in recent years. Manufacturers claim that the products, in the form of drinks, shots, supplements, and gels, enhance physical and cognitive performance, while users believe the products promote concentration, alertness, and fun. Most of these products contain caffeine, a mild psychostimulant, as their foremost active ingredient. However, they also contain additional ingredients, e.g., carbohydrates, amino acids, herbal extracts, vitamins, and minerals, often in unspecified amounts and labeled as an "energy blend." It is not clear whether these additional ingredients provide any physical or cognitive enhancement beyond that provided by caffeine alone. This article reviews the available empirical data on the interactive effects of these ingredients and caffeine on sleep and cognitive performance and suggests objectives for future study.
... Another issue that deserves attention is that most experiments that investigated the cognitive effects of caffeine were carried out after an overnight fast, which in itself can impair cognitive performance (see Gibson and Green, 2002;Messier, 2004). Furthermore, some authors suggest that caffeine and glucose can act synergically to enhance attentional performance Serra-Grabulosa et al., 2010;Scholey and Kennedy, 2004), possibly because caffeine modulates glucose metabolism (Greer et al., 2001;Keijzers et al., 2002;Thong et al., 2002;Moisey et al., 2008;Young and Benton, 2013) and cognitively demanding processing is dependent on blood sugar levels (see Donohoe and Benton, 1999;Scholey et al., 2001;Messier, 2004). As caffeine-containing products are commonly consumed with food, providing data about the effects of caffeine under meal and fasting conditions may also aid in the better understanding of the effects of caffeine in everyday use. ...
... Differently, regarding simple and sustained attention, we hypothesized that personalized acute habitual doses of caffeine would improve performance because there is a large body of data that supports these effects, even in small doses (see Einöther and Giesbrecht, 2013). Furthermore, because of the suggestions that there are synergic cognitive effects of caffeine and glucose Serra-Grabulosa et al., 2010;Scholey and Kennedy, 2004) and that caffeine can increases blood glucose levels (Greer et al., 2001;Keijzers et al., 2002;Thong et al., 2002;Moisey et al., 2008;Young and Benton, 2013), we expected that these effects would be more pronounced when subjects were fed. Regarding subjective measures, we believed that they would not indirectly affect cognitive performance because this occurs mainly when participants are under conditions that impair cognitive performance, such as sleep (e.g., Newman et al., 2013) and caffeine (e.g., Smith, 2002) deprivation. ...
... Regarding the relations of caffeine and the meal, contrary to some studies (Moisey et al., 2008;Young and Benton, 2013), we did not show acute caffeine- related glucose enhancement or changes in insulin resistance in the participants who were fed (see Greer et al., 2001;Keijzers et al., 2002;Thong et al., 2002;Skinner et al., 2012). However, our finding of lack of glucose enhancement by caffeine corroborates other work that investigated the combined effect of glucose and fixed doses of caffeine on attentional measures (Scholey and Kennedy, 2004;Adan and Serra-Grabulosa, 2010;Serra-Grabulosa et al., 2010), possibly because (i) both the current and these latter studies did not measure glucose often enough to obtain a curve with sufficient power to show these effects or (ii) these effects are observed only with higher caffeine and/or glucose doses. What we can say is that if habitual caffeine doses change glucose homeostasis, this effect is less sensitive to caffeine than are attentional/executive effects. ...
Article
Caffeine is widely used, often consumed with food, and improves simple and complex/executive attention under fasting conditions. We investigated whether these cognitive effects are observed when personalized habitual doses of caffeine are ingested by caffeine consumers, whether they are influenced by nutriments and if various executive domains are susceptible to improvement. This was a double-blind, placebo-controlled study including 60 young, healthy, rested males randomly assigned to one of four treatments: placebo fasting, caffeine fasting, placebo meal and caffeine meal. Caffeine doses were individualized for each participant based on their self-reported caffeine consumption at the time of testing (morning). The test battery included measures of simple and sustained attention, executive domains (inhibiting, updating, shifting, dual tasking, planning and accessing long-term memory), control measures of subjective alterations, glucose and insulin levels, skin conductance, heart rate and pupil dilation. Regardless of meal intake, acute habitual doses of caffeine decreased fatigue, and improved simple and sustained attention and executive updating. This executive effect was not secondary to the habitual weekly dose consumed, changes in simple and sustained attention, mood, meal ingestion and increases in cognitive effort. We conclude that the morning caffeine "fix" has positive attentional effects and selectively improved executive updating whether or not caffeine is consumed with food. Copyright © 2015 John Wiley & Sons, Ltd.
... Eleven studies met the inclusion criteria for this review, their characteristics are summarised in Tables 1 and 2. The studies were conducted in several countries including UK (n = 3), Canada (n = 2), USA (n = 2), Australia (n = 1), Spain (n = 1), Switzerland (n = 1) and Korea (n = 1). Six studies were conducted with healthy adult participants (An, Jung, Kim, Lee, & Kim, 2015;Brown & Riby, 2013;Parent et al., 2011;Riby et al., 2008;Serra-Grabulosa, Adan, Falcon, & Bargallo, 2010;Zanchi et al., 2018). Three studies were conducted with healthy elderly samples (Gagnon et al., 2012;Knott, Messier, Mahoney, & Gagnon, 2001;Scholey et al., 2015). ...
... Two studies reported spectral analysis of resting EEG Knott et al., 2001). Four studies were conducted using task related functional magnetic resonance imaging (fMRI: Parent et al., 2011;Serra-Grabulosa et al., 2010;Stone et al., 2005;Zanchi et al., 2018), of which two also reported measuring fMRI connectivity (Parent et al., 2011;Zanchi et al., 2018). One study was conducted using functional near infrared spectroscopy (fNIRS: Gagnon et al., 2012). ...
... Ten of the studies employed a within-subject repeated measures design in which participants serve as their own control (crossover design), only one used a between-subject design (Brown & Riby, 2013). In one repeated-measures study, testing pre-and post-ingestion was conducted on the same day (Serra-Grabulosa et al., 2010), in all other studies with repeated-measures, testing of the active and placebo drink occurred on separate days. In seven studies participants were asked to attend the lab after at least eight hours of fasting (usually overnight: An et al., 2015;An et al., 2015;Gagnon et al., 2012;Knott et al., 2001;Parent et al., 2011;Serra-Grabulosa et al., 2010;Scholey et al., 2015;Stone et al., 2005;Zanchi et al., 2018) and in three studies participants were instructed to fast for two hours prior to the testing sessions (Brown & Riby, 2013;Riby et al., 2008;Smith et al., 2009). ...
Article
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A transient improvement in cognitive performance can be observed following the ingestion of a glucose drink, a phenomenon known as the ‘glucose facilitation effect’. The effect has been studied thoroughly in the last three decades, but its neural underpinnings remain a matter of speculation. A systematic review was conducted to evaluate the current evidence from studies applying neuroimaging or neurophysiological methods to investigate the glucose enhancement effect. Eleven studies met the inclusion criteria of using neuroimaging in conjunction with cognitive outcomes. Six studies employed electroencephalography (EEG), four used functional magnetic resonance imaging (fMRI) and one employed functional near-infrared spectroscopy (fNIRS). All but one study reported modulation of neurophysiology or neuroimaging markers following glucose, while only five studies reported significant changes in cognitive outcomes. The evidence suggests that glucose administration enhances neurocognitive markers of episodic memory and attentional processes underpinned by medial temporal and frontal activation, sometimes in the absence of measurable behavioural effects. Further exploration of glucose facilitation using neuroimaging measures with increased sample sizes is warranted to replicate these findings.
... Adan and Serra-Grabulosa [191] reported a facilitative effects of 75 mg:75 g caffeine:glucose on a sequential RT attentional task which was not demonstrated following intake of caffeine and glucose in isolation. Serra-Grabulosa et al. [192] reported that the same combined dose decreased neural (blood-oxygen-level dependent; BOLD) activation in areas of the prefrontal cortex associated with sustained attention processes (vs. placebo), which suggests enhanced efficiency of the attentional system. ...
... However, this effect must be treated with caution as no objective, interactive behavioral effects were demonstrated. Four studies failed to demonstrate interactive effects of caffeine and glucose (caffeine:glucose: 75 mg:75 g [192]; 200 mg:50 g [193]; 80 mg:39 g [194]; 200 mg:50 g [195]). The addition of 50g CHO (white bread) to a 200 mg caffeine capsule counteracted enhanced performance on a vigilance task compared to caffeine administered in isolation [195]. ...
... Serra-Grabulosa et al. 2010 [192] 40 (18)(19)(20)(21)(22)(23)(24)(25) Between ( x-effect; √-no effect; GL-glycemic load; WM-working memory; CBG-capillary blood glucose; HR-heart rate; POMS-Profile of Mood States; CGMScontinuous glucose monitoring system; CPT-continuous performance task. ...
Article
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This review examines the effects of carbohydrates, delivered individually and in combination with caffeine, on a range of cognitive domains and subjective mood. There is evidence for beneficial effects of glucose at a dose of 25 g on episodic memory, but exploration of dose effects has not been systematic and the effects on other cognitive domains is not known. Factors contributing to the differential sensitivity to glucose facilitation include age, task difficulty/demand, task domain, and glucoregulatory control. There is modest evidence to suggest modulating glycemic response may impact cognitive function. The evidence presented in this review identifies dose ranges of glucose and caffeine which improve cognition, but fails to find convincing consistent synergistic effects of combining caffeine and glucose. Whilst combining glucose and caffeine has been shown to facilitate cognitive performance and mood compared to placebo or glucose alone, the relative contribution of caffeine and glucose to the observed effects is difficult to ascertain, due to the paucity of studies that have appropriately compared the effects of these ingredients combined and in isolation. This review identifies a number of methodological challenges which need to be considered in the design of future hypothesis driven research in this area.
... 2009), increasing alertness (Smit et al. 2004;Haskell et al. 2005;Rogers2008 ), and increasing vigor (Arciero and Ormsbee 2009;Souissi et al. 2013Souissi et al. , 2012. Caffeine has also been suggested to improve reaction time (Haskell et al. 2005;Adan and Serra-Grabulosa, 2010;Souissi et al. 2013Souissi et al. , 2012Souissi et al. et al. 2013Santos et al. 2014). Other physiological effects of caffeine are not as clear cut. ...
... The major components of Starbucks DoubleShot® are caffeine and glucose (Table 1). Short-term studies (30 minutes post caffeine/glucose consumption) showed some degree of a synergism between caffeine and glucose: increasing attention and memory (Scholey and Kennedy 2004), increased efficiency of attention system (Serra-Grabulosa et al. 2010), and improved reaction times (Adan and Serra-Grabulosa 2010). However, Smit et al. (2004) did not find significant synergy between glucose and caffeine. ...
... The biggest difference between SDS and other caffeine types is the additional glucose content of the SDS. Synergistic activity of the glucose/caffeine combination has demonstrated a degree of synergy in the short-term by increasing attention and energy and decreasing reaction time (Adan and Serra-Grabulosa, 2010;Serra-Grabulosa et al. 2010;Scholey and Kennedy, 2004), but an antagonist effect has been observed longer term (Young and Benton, 2013). Benton et al. (2003) suggested that consuming foods with a high glycemic index resulted in subjects being less energetic as the morning went on and subjects who consumed foods with a low glycemic index resulted in better memory. ...
Article
Although college students’ caffeine consumption has increased over the last decade, studies have not yet determined the time frame in which caffeine exerts its effects nor the impact of the vehicle by which caffeine is consumed. Sixty college students were randomly divided into one placebo (flour) and three caffeine treatment groups: 5-Hour Energy ®, Starbucks DoubleShot ®, or caffeine powder; all dosed at 3 mg caffeine/kg of body weight. A battery of tests was performed prior to dosing and repeated 2.5 and 5 hours post treatment. Mood was self-reported on a scale of 1-100 for happiness, alertness and focus. Cognitive function was assessed by Stroop and memory tests. Reaction time, heart rate, blood glucose, and electroencephalogram were recorded. All initial measurements across groups and group baselines vs 2.5 and 5 hour results were analyzed by ANOVA followed, when indicated, by post hoc t-tests at 95% confidence levels and only significant results are reported. All caffeine groups had elevations in mood and faster reaction times at 2.5 hours (most effects sustained for 5 hours). The 5-Hour Energy® group rated alertness higher than other caffeine treatments, and was the only group to demonstrate decreases in alpha waves, memory improvements, and impaired glucose homeostasis. All caffeine groups had improved cognition with decreased Stroop test time and the caffeine powder and 5-Hour Energy ® groups had improved Stroop test accuracy at 2.5 hours. The 5-Hour Energy shot ® had the greatest proportion of sustained caffeine effects across test parameters.
... Caffeine, a stimulant, is arguably the most widely used psychoactive substance in the world (Serra-Grabulosa et al., 2010). This drug is a direct receptor antagonist of adenosine, an inhibitory neuromodulator, in the brain and indirectly results in an increase of plasma catecholamines (Kamimori et al., 2000;Snyder and Sklar, 1984). ...
... Many studies have investigated the effects of caffeine on human behavior and cognition. It has been found to increase subjective alertness and reduce fatigue as well as have beneficial effects on measures of reaction time, sustained attention, and real-life motor tasks (Kaplan et al., 1997;Serra-Grabulosa et al., 2010). Caffeine has been demonstrated to reverse psychomotor impairments induced by alcohol or benzodiazepines and, theoretically, may also counteract antihistamine-induced psychomotor impairments in behavior (Azcona et al., 1995;Drake et al., 2003;Hasenfratz et al., 1993;Johnson et al., 1990;Kerr et al., 1991;Liguori and Robinson, 2001;Roache and Griffiths, 1987). ...
... In addition, caffeine promotes wakefulness by enhancing cAMP levels (Wu et al., 2009). These effects of caffeine on neural activation and neurotransmission may be related to the restoration of chlorpheniramine-impaired vigilance and sustained attention (Serra-Grabulosa et al., 2010). ...
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This study aimed to evaluate the effects of chlorpheniramine on psychomotor performance and the counteracting effects of caffeine on those sedative antihistamine actions. Sixteen healthy young men participated in this study. Using a double-blind placebo-controlled crossover design, each subject was administered one of the following conditions in a random order with a one-week interval: 'placebo-placebo', '4 mg of chlorpheniramine-placebo', 'placebo-200 mg of caffeine' or '4 mg of chlorpheniramine-200 mg of caffeine'. Before and after the treatments, psychomotor functions were assessed using a battery of tests. Additionally, subjective responses were assessed using a visual analogue scale (VAS). Psychomotor performance changed over time in different ways according to the combination of study medications. In the 'chlorpheniramine-placebo' condition, reaction times of the compensatory tracking task were significantly impaired compared with the other three conditions. In addition, the number of omission errors of the continuous performance test were significantly greater compared with the 'placebo-caffeine' condition. However, the response pattern of the 'chlorpheniramine-caffeine' condition was not significantly different from that of the 'placebo-placebo' condition. Changes of VAS for sleepiness were significantly greater in the 'chlorpheniramine-placebo' condition compared with the other three conditions. In conclusion, chlorpheniramine significantly increases subjective sleepiness and objectively impairs psychomotor performance. However, caffeine counteracts these sedative effects and psychomotor impairments.
... Coffee is a one of the most consumed beverages in the world, and in particular the effects on both physiology and behaviour of its well-known active compound caffeine have been studied extensively. Caffeine is known to exert positive effects on cognitive performance such as reaction time, alertness and sustained attention Haskell et al., 2005Haskell et al., , 2008Lieberman et al., 1987;Lorist et al., 1995;Rees et al., 1999;Serra-Grabulosa et al., 2010;Smit and Rogers, 2000;Swift and Tiplady, 1988). However, the majority of research studying the effects of caffeine on cognitive performance involves high levels of caffeine, ranging from a dose of 200 mg up to 500 mg (Einother and Giesbrecht, 2013), whereas fewer efforts have been made in studying the effects of lower caffeine dose (<75 mg) on cognition (Childs and De Wit, 2006;Durlach, 1998;Smith, 2006, 2007;Lieberman et al., 1987;Smith, 2009;Yeomans et al., 2002). ...
... Specifically, performance on the co-primary outcome sustained attention tests, the RVIP task (reaction time performance and number of correct hits) and the Mackworth Clock test (index of stimulus sensitivity, number of correct hits and the reaction time of the correct responses), were significantly improved in the first 70 minutes post caffeine intake compared with placebo. These results are in line with previous research that has shown low-dose caffeine improves sustained attention performance (Adan and Serra-Grabulosa, 2010; Smith, 2006, 2007;Lieberman et al., 1987;Serra-Grabulosa et al., 2010;Smith, 2009Yeomans et al., 2002. Moreover, the present findings highlight that sustained attention performance improved with tasks longer than 5 minutes duration (i.e. ...
Article
Caffeine induces positive effects on sustained attention, although studies assessing the acute effects of low caffeine dose (<75 mg) on sustained attention are limited and use short-term tests. Therefore, we investigated the acute effects of a 60 mg dose of caffeine on sustained attention in tests lasting up to 45 minutes using 82 low or non-caffeine-consuming healthy male (n=41) and female (n=41) adults aged between 40 and 60 years. Vigilance was measured using Mackworth Clock test, Rapid Visual Information Processing Test, adaptive tracking test, saccadic eye movement and attention switch test. Effects on mood and fatigue were analysed using Bond and Lader and Caffeine Research visual analogue scales, and Samn–Perelli questionnaire. Saliva sampling was performed for both compliance and caffeine pharmacokinetic analysis. Administration of a 60 mg caffeine dose resulted in a significant improvement in sustained attention compared with the placebo. Also a significantly improved peak saccadic velocity and reaction time performance was found, and decreased error rate. Significantly increased feelings of alertness, contentment and overall mood after caffeine treatment compared with placebo were observed. This study demonstrated that in healthy adult subjects oral administration of a single 60 mg caffeine dose elicited a clear enhancement of sustained attention and alertness, measured both in multiple objective performances and in subjective scales.
... Functional magnetic resonance imaging (fMRI) is available in the human 5C-CPT. A fronto-striatal and parietal cerebral network is activated during task performance of the 5C-CPT (Eyler et al., 2011 ), consistent with other human CPTs (Grabulosa et al., 2010; Schneider et al., 2010 ). Importantly, differential activation/deactivation patterns are observed depending on whether a target or nontarget trial type is presented (Eyler et al., 2011). ...
... Caffeine is well known to enhance aspects of both sustained and selective attention, as shown with behavioral measures 145 as well as with electroencephalography and event-related potentials. [146][147][148][149] Caffeine commonly reduces reaction time and increases accuracy and has also been demonstrated to reduce omission and commission errors. The Stroop test and DSSTs have been used in various intervention studies with isoflavones, polyphenols, and n-3 (Table 2), although some studies may refer to these tests as executive function tasks or processing speed tasks. ...
Article
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This review is an output of the International Life Sciences Institute (ILSI) Europe Marker Initiative, which aims to identify evidence-based criteria for selecting adequate measures of nutrient effects on health through comprehensive literature review. Experts in cognitive and nutrition sciences examined the applicability of these proposed criteria to the field of cognition with respect to the various cognitive domains usually assessed to reflect brain or neurological function. This review covers cognitive domains important in the assessment of neuronal integrity and function, commonly used tests and their state of validation, and the application of the measures to studies of nutrition and nutritional intervention trials. The aim is to identify domain-specific cognitive tests that are sensitive to nutrient interventions and from which guidance can be provided to aid the application of selection criteria for choosing the most suitable tests for proposed nutritional intervention studies using cognitive outcomes. The material in this review serves as a background and guidance document for nutritionists, neuropsychologists, psychiatrists, and neurologists interested in assessing mental health in terms of cognitive test performance and for scientists intending to test the effects of food or food components on cognitive function.
... These data are consistent with the hypothesis that a caffeine– glucose drink can increase the amount of attentional resources , which can be allocated to task performance. This is in broad agreement with the results of a functional magnetic resonance imaging study showing lower levels of neural activation following a caffeine–glucose combination (albeit at different levels) than placebo or caffeine or glucose alone (Serra Grabulosa et al., 2010). Regarding the mechanisms underlying superior multi-tasking, we can be confident that the double blind was effective and that expectations as to conditions did not influence results. ...
Article
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Background This study assessed the effects of two doses of glucose and a caffeine–glucose combination on mood and performance of an ecologically valid, computerised multi-tasking platform.Materials and methodsFollowing a double-blind, placebo-controlled, randomised, parallel-groups design, 150 healthy adults (mean age 34.78 years) consumed drinks containing placebo, 25 g glucose, 60 g glucose or 60 g glucose with 40 mg caffeine. They completed a multi-tasking framework at baseline and then 30 min following drink consumption with mood assessments immediately before and after the multi-tasking framework. Blood glucose and salivary caffeine were co-monitored.ResultsThe caffeine–glucose group had significantly better total multi-tasking scores than the placebo or 60 g glucose groups and were significantly faster at mental arithmetic tasks than either glucose drink group. There were no significant treatment effects on mood. Caffeine and glucose levels confirmed compliance with overnight abstinence/fasting, respectively, and followed the predicted post-drink patterns.Conclusion These data suggest that co-administration of glucose and caffeine allows greater allocation of attentional resources than placebo or glucose alone. At present, we cannot rule out the possibility that the effects are due to caffeine alone Future studies should aim at disentangling caffeine and glucose effects. © 2014 The Authors. Human Psychopharmacology: Clinical and Experimental published by John Wiley & Sons, Ltd.
... Four separate groups of researchers have reported faster choice reaction times following caff eine consumption ( Giles, Mahoney, Brunyé, Gardony, Taylor, & Kanarek, 2012 ). Serra-Grabulosa, Adan, Falcón, and Bargalló (2010) found that a combination of caff eine and glucose had a decrease in activation of the bilateral parietal and left prefrontal cortex, suggesting that this may increase effi ciency of the attentional system. A position statement published by the International Society of Sports Nutrition (ISSN; Campbell, Wilborn, La Bounty, Taylor, Nelson, Greenwood, et al ., 2013 ) stated that energy shots may have some ergogenic eff ect due to additive eff ects of caff eine and carbohydrates. ...
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-This study assessed the effect of energy shots on selected fine motor tasks. The participants were college-age male (n = 19; M age = 20.5 yr., SD = 0.7) and female (n = 21; M age = 21.1 yr., SD = 0.7) volunteers who were assessed on hand steadiness, choice reaction time, rotary pursuit, and simple reaction time. The energy shots group scored significantly poorer on the hand steadiness tests and significantly better on choice reaction time and simple reaction time tests. The enhanced reaction time and disruption in hand steadiness afforded by energy shots would not be apparent in many gross motor activities, but it is possible that reaction time improvement could be beneficial in sports that require quick, reflexive movements. However, the potential adverse psychological and physiological effects warrant discretionary use of such products.
... Several studies have reported evidence consistent with glucose producing a short-term increase in the efficient use of limited attentional resources (Benton et al. 1987(Benton et al. , 1994Flint and Turek 2003;Fucetola et al. 1999;Rao et al. 2005;Riby et al. 2008;Scholey et al. 2009;Serra-Grabulosa et al. 2010) and, given participants were explicitly required to remember object-location pairings, this could be one possible mechanism for improved binding. Specifically, our task requires the maintenance of multiple object-location pairs and participants may have strategically attended to a subset of these pairs by prioritizing resources. ...
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Rationale There is evidence that glucose temporarily enhances cognition and that processes dependent on the hippocampus may be particularly sensitive. As the hippocampus plays a key role in binding processes, we examined the influence of glucose on memory for object-location bindings. Objective This study aims to study how glucose modifies performance on an object-location memory task, a task that draws heavily on hippocampal function. Methods Thirty-one participants received 30 g glucose or placebo in a single 1-h session. After seeing between 3 and 10 objects (words or shapes) at different locations in a 9 × 9 matrix, participants attempted to immediately reproduce the display on a blank 9 × 9 matrix. Blood glucose was measured before drink ingestion, mid-way through the session, and at the end of the session. Results Glucose significantly improves object-location binding (d = 1.08) and location memory (d = 0.83), but not object memory (d = 0.51). Increasing working memory load impairs object memory and object-location binding, and word-location binding is more successful than shape-location binding, but the glucose improvement is robust across all difficulty manipulations. Within the glucose group, higher levels of circulating glucose are correlated with better binding memory and remembering the locations of successfully recalled objects. Conclusions The glucose improvements identified are consistent with a facilitative impact on hippocampal function. The findings are discussed in the context of the relationship between cognitive processes, hippocampal function, and the implications for glucose’s mode of action.
... The beneficial effects of glucose have been observed for a wide range of experimental settings and cognitive tasks across different medical populations and species. In humans, an enhancement effect following glucose administration has been shown for: cognitive performance resulting in a reduction of reaction times (Adan and Serra-Grabulosa, 2010); selective and sustained attention and control (Gagnon et al., 2010; Serra-Grabulosa et al., 2010 ); continuous performance tests of attention (Flint, 2004); cognitively demanding tasks (Scholey et al., 2001 ); and learning and memory (for an extensive review see Smith et al., 2011). In clinical populations with severe cognitive deficits, the administration of glucose has been shown to improve cognitive function, for example , memory performance in Alzheimer's disease (Manning et al., 1993; Messier et al., 1997), although there are also negative reports (Craft et al., 1999). ...
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This study aimed to directly assess the effect of changes in blood glucose levels on the psychological processing of emotionally charged material. We used functional magnetic resonance imaging (fMRI) to evaluate the effect of blood glucose levels on three categories of visually presented emotional stimuli. Seventeen healthy young subjects participated in this study (eight females; nine males; body weight, 69.3 ± 14.9 kg; BMI, 22 ± 2.7; age, 24 ± 3 years), consisting of two functional MRI sessions: (1) after an overnight fast under resting conditions (before glucose administration); (2) after reaching the hyperglycemic state (after glucose administration). During each session, subjects were presented with visual stimuli featuring funny, neutral, and sad content. Single-subject ratings of the stimuli were used to verify the selection of stimuli for each category and were covariates for the fMRI analysis. Analysis of the interaction effect of the two sessions (eu- and hyperglycemia), and the emotional categories accounting for the single-subject glucose differences, revealed a single activation cluster in the hypothalamus. Analysis of the activation profile of the left amygdala corresponded to the three emotional conditions, and this profile was obtained for both sessions regardless of glucose level. Our results indicate that, in a hyperglycemic state, the hypothalamus can no longer respond to emotions. This study offers novel insight for the understanding of disease-related behavior associated with dysregulation of glucose and glucose availability, potentially offering improved diagnostic and novel therapeutic strategies in the future.
... Researchers in cognitive psychology and neuroscience have long studied the impact of blood glucose fluctuations on the brain, cognition, and behavior 1 . For example, researchers have found that fluctuations in blood glucose predict differences in memory (verbal, digit span, working, and episodic) [1][2][3][4][5] , attention 6,7 , puzzle solving 8 , and performance on tasks of varying levels of cognitive demand 2,9,10 . This research finds that increasing blood glucose enhances attention and memory, and that these effects are strongest when working on cognitively demanding tasks, and in those of older age 1,3 . ...
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Much research in social psychology has investigated the impact of bodily energy need on cognition and decision-making. As such, blood glucose, the body's primary energy source, has been of special interest to researchers for years. Fluctuations in blood glucose have been linked to a variety of changes in cognitive and behavioral processes, such as self-control, political attitudes, and eating behavior. To help meet growing interest in the links between bodily energy need and these processes, this manuscript offers a simple methodology to experimentally manipulate blood glucose using a fasting procedure followed by administration of a sugar-sweetened, unsweetened, or artificially-sweetened beverage. This is followed by presentation of a method for measuring resulting changes in implicit cognition using a lexical decision-task. In this task, participants are asked to identify whether strings of letters are words or non-words and response latencies are recorded. Sample results from a recent publication are presented as an example of the applications for the experimental manipulation of blood glucose and the lexical decision task measures.
... Participants in the highest quartile of DDS had the lowest caffeine intake. Caffeine generally was found to improve attention, concentration, alertness and reduce fatigue in children and adults in other studies (44)(45)(46) . The indirect effects of caffeine on concentration are attributed to its cognitive-promoting properties (45) . ...
Article
Attention is a complex cognitive function that is necessary for learning, for following social norms of behaviour and for effective performance of responsibilities and duties. It is especially important in sensitive occupations requiring sustained attention. Improvement of dietary diversity (DD) is recognised as an important factor in health promotion, but its association with sustained attention is unknown. The aim of this study was to determine the association between auditory and visual sustained attention and DD. A cross-sectional study was carried out on 400 women aged 20–50 years who attended sports clubs at Tehran Municipality. Sustained attention was evaluated on the basis of the Integrated Visual and Auditory Continuous Performance Test using Integrated Visual and Auditory software. A single 24-h dietary recall questionnaire was used for DD assessment. Dietary diversity scores (DDS) were determined using the FAO guidelines. The mean visual and auditory sustained attention scores were 40·2 ( sd 35·2) and 42·5 ( sd 38), respectively. The mean DDS was 4·7 ( sd 1·5). After adjusting for age, education years, physical activity, energy intake and BMI, mean visual and auditory sustained attention showed a significant increase as the quartiles of DDS increased ( P =0·001). In addition, the mean subscales of attention, including auditory consistency and vigilance, visual persistence, visual and auditory focus, speed, comprehension and full attention, increased significantly with increasing DDS ( P <0·05). In conclusion, higher DDS is associated with better visual and auditory sustained attention.
... There has only been limited study of the interaction between caffeine and glucose consumption. Serra-Grabulosa et al. (2010) used functional magnetic resonance imaging whilst monitoring a test of sustained attention. After half an hour, a drink combining caffeine (75 mg) and glucose (75 g) resulted in a similar performance to when only one of these constituents had been consumed. ...
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Rationale Energy drinks contain glucose and caffeine, although in the longer term both adversely influence blood glucose homeostasis, with the unconsidered potential to have adverse consequences for cognition and mood. Objective The objective of this study was to consider the influence on interstitial glucose levels, mood and cognition of drinks differing in their caffeine content and glycaemic load. Methods Ninety minutes after a standard breakfast, a yoghurt-, glucose- or water-based drink, with or without 80 mg of caffeine, was consumed. Results The consumption of caffeine negatively influenced glucose homeostasis: that is, irrespective of the vehicle, caffeine consumption resulted in elevated levels of blood glucose throughout the study. Thirty minutes after consuming caffeine and water, rather than water alone, greater subjective energy was reported. However, after 90 and 150 min, caffeine administered in water increased tiredness, hostility and confusion. In contrast, combining caffeine with a yoghurt-based drink increased energy, agreeableness and clearheadedness later in the morning. There were no effects of caffeine on ratings of mood when it was taken with glucose. Caffeine, irrespective of vehicle, resulted in better memory, quicker reaction times in the choice reaction time test and the working memory task, and better and quicker responses with the vigilance task. Conclusion Further research should consider how caffeine interacts with macronutrients and the timescale over which such effects occur.
... In a substantial number of studies, caffeine consumption (in doses ranging from 50 to 400 mg) has been shown to improve attention performance on various simple and complex tasks for volunteers who normally do not consume caffeine (Richardson et al. 1995;Haskell et al. 2005;Smith 2006, 2007;Smith et al. 2006) or low habitual thus non-dependent caffeine consumers de Wit 2006, 2008;Hewlett and Smith 2006;2007;Brunye et al. 2010a). Fewer studies have found no significant effects of a low dose of caffeine (75 mg) in low habitual consumers (Adan and Serra-Grabulosa 2010; Kennedy and Haskell 2011;Serra-Grabulosa et al. 2010). Finally, only one study found significant effects of a range of caffeine doses, but only for high habitual consumers (Smit and Rogers 2000). ...
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Rationale Despite the large number of studies on the behavioural effects of caffeine, an unequivocal conclusion had not been reached. In this review, we seek to disentangle a number of questions. Objective Whereas there is a general consensus that caffeine can improve performance on simple tasks, it is not clear whether complex tasks are also affected, or if caffeine affects performance of the three attention networks (alerting, orienting and executive control). Other questions being raised in this review are whether effects are more pronounced for higher levels of caffeine, are influenced by habitual caffeine use and whether there effects are due to withdrawal reversal. Method Literature review of double-blind placebo controlled studies that assessed acute effects of caffeine on attention tasks in healthy adult volunteers. Results Caffeine improves performance on simple and complex attention tasks, and affects the alerting, and executive control networks. Furthermore, there is inconclusive evidence on dose-related performance effects of caffeine, or the influence of habitual caffeine consumption on the performance effects of caffeine. Finally, caffeine’s effects cannot be attributed to withdrawal reversal. Conclusions Evidence shows that caffeine has clear beneficial effects on attention, and that the effects are even more widespread than previously assumed.
... Moreover, their carbohydrate content (between 6% and 8%) increases glucose levels in the body, which is essential for correct physical and cognitive performance [24,29]. The consumption of low doses of caffeine with glucose, as contained in soft drinks, could also be a better strategy than drinking more water in order to boost performance in sustained attention, learning and memory tasks [25,53]. Last, energy drinks that contain both glucose and caffeine together with other psychoactive substances (e.g., taurine or ginseng) that improve cognitive performance [54,55], should also be assessed. ...
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No matter how mild, dehydration is not a desirable condition because there is an imbalance in the homeostatic function of the internal environment. This can adversely affect cognitive performance, not only in groups more vulnerable to dehydration, such as children and the elderly, but also in young adults. However, few studies have examined the impact of mild or moderate dehydration on cognitive performance. This paper reviews the principal findings from studies published to date examining cognitive skills. Being dehydrated by just 2% impairs performance in tasks that require attention, psychomotor, and immediate memory skills, as well as assessment of the subjective state. In contrast, the performance of long-term and working memory tasks and executive functions is more preserved, especially if the cause of dehydration is moderate physical exercise. The lack of consistency in the evidence published to date is largely due to the different methodology applied, and an attempt should be made to standardize methods for future studies. These differences relate to the assessment of cognitive performance, the method used to cause dehydration, and the characteristics of the participants.
... A working memory study (29) has found that response in bilateral medial frontopolar cortex and right anterior cingulate cortex is increased after caffeine intake, suggesting that caffeine can modulate neuronal activity in a network of brain areas associated with executive and attentional functions during working memory processes. Serra-Grabulosa et al. (30) have reported that caffeine has modest effect on sustained attention-task activation not directly inferred in a statistical way. ...
... Sugar (glucose) is used in the present study in coffee robusta while coffee arabica (Qahwa) was served without sugar. Previously Serra-Grabulosa et al. (2010) quoted that combined caffeine (coffee robusta) and glucose could increase the efficiency of the attentional system studies. Serra-Grabulosa (Serra-Grabulosa et al. 2010) used 75 g sugar that is far higher than the levels found in sweetened coffee robusta. ...
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The comparative effects of coffee robusta and coffee arabica (Qahwa) on different attention and memory related assignments were measured in a double-blind study of 300 healthy young adult women who were randomly assigned to one of three different drinks: Group I (coffee robusta sachet dissolved in 100 ml of hot water): Group II (coffee arabica): and group III (100 ml water only). Cognitive function was assessed by standardized tests. Several monitoring cognitive tests and tasks were specifically chosen and performed to investigate the comparative effects of coffee robusta (CR) and coffee arabica (Qahwa; AC) on sleepiness (sleep and clear headed scale), attention (trail A & B, symbol digit, letter cancellation), general cognitive ability (stroop test) and memory (card test). Data was interpreted by analysis of variance (ANOVA). The present study revealed that coffee robusta has beneficial effects on attention, general cognitive ability and memory. Higher though non-significant cognitive scores were associated with coffee robusta consumption. Although, consumption of coffee arabica (Qahwa) has significant effects (P < 0.05) on sleepiness, attention, general cognitive ability and memory and it significantly improve reaction time and correct responses. Since different tasks were related to the sustained attention and working memory processes, results would suggest that coffee arabica (qahwa) could increase the memory and efficiency of the attentional system might be due to the presence of chlorogenic acids (CGA) which are found in less quantity in coffee robusta. However, more studies using larger samples and different tasks are necessary to better understand the effects of coffee robusta and arabica (Qahwa) on attention and memory.
... Caffeinated drinks consumption has grown dramatically in the last decade, turning caffeine into one of the most commonly consumed psychoactive substances worldwide (Heckman et al. 2010). Caffeine acts on dopaminergic activity affecting mood, attention, executive functioning, and regulation of behavioral traits (Ishak et al. 2012;Serra-Grabulosa et al. 2010;Volkow et al. 2015). Several studies have reported that caffeine consumption is significantly associated with depressive symptoms and that it decreases the risk of depression (Ruusunen et al. 2010;Sunram-Lea et al. 2012;Wang et al. 2016). ...
Article
Among the factors that contribute to the onset and maintenance of depressive disorders, rhythmicity of symptoms and consumption of caffeine have recently gained attention. The current study aimed to examine the differential rhythmicity of relevant variables in a sample of young participants, considering the presence of depressive symptomatology and the frequency of caffeinated drinks consumption. A significant 24-hour differential rhythmicity of mood, cognitive and physiological variables was found indicating an evening peak pattern in the participants with depressive symptoms. Interestingly, caffeinated drinks consumption was differentially associated with self-perceived peaks, according to the presence of depressive symptomatology. Our findings are among the first reports about the potential association of the 24-hours rhythmicity of relevant mood-related variables, depressive symptoms, and caffeine intake. These results support the view that the identification of risk factors for depression, and the application of novel measurements and analysis methods in the development of new preventive strategies should be a public health priority.
... Subjects with chronic disorders, nervous system disorders, those under chronic medication, history of mental illness, or regular alcohol consumers, were excluded from the study. Participants were required to avoid caffeine intake for a minimum of 12 h prior to the start of the fMRI session, as caffeine influences performance [20] and BOLD signal [21]. The study was approved by the ethics committee of the Hospital Clínic de Barcelona. ...
... Subjects with chronic disorders, nervous system disorders, those under chronic medication, history of mental illness, or regular alcohol consumers, were excluded from the study. Participants were required to avoid caffeine intake for a minimum of 12 h prior to the start of the fMRI session, as caffeine influences performance [20] and BOLD signal [21]. The study was approved by the ethics committee of the Hospital Clínic de Barcelona. ...
... Complex behavioral and biochemical effects can be triggered extensively by caffeine throughout the human body [3]. Accordingly, many studies have focused on effects of caffeine on central nervous system (CNS) and cognitive processes [4][5][6][7][8]. Wentz and Magavi [9] have reported that extended administration of supraphysiological doses of caffeine has several biochemical effects. ...
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Objectives.: Past several studies have proven that caffeine facilitates attentional enhancement by acting as an adenosine antagonist once it is absorbed by the body, resulting in improved psycho-behavioral function. Modern clinical olfactory function tests are usually assessed by psychophysical tests but due to a paucity of data, the influence of enhanced attention by caffeine on olfactory function still remains unclear. The objective of this study was to compare results of cognitive function (attention) and olfactory function before and after caffeine administration in order to analyze effects of caffeine on olfactory function in normosmic subjects. Methods.: This study enrolled 49 participants of Konkuk University Hospital with a mean age of 27.7 years who had patent olfactory clefts and no olfactory dysfunction from May 2015 to February 2016. Subjects were restrained from caffeine 10 hours before the test. On day 1, participant's subjective olfactory function was evaluated before and after uptake of either caffeinated or decaffeinated coffee using visual analog scale (VAS) score, minimum cross-sectional area (MCA) measured by acoustic rhinometry, and the Korean version of Sniffin' Stick II (KVSS II). Evaluation of participant's attentional degree was measured by d2 test. On day 2, the same procedure was carried out with counterpart substance. The type of coffee initially administrated was randomly selected. Results.: After administration, caffeinated coffee resulted in significant attentional enhancement than decaffeinated coffee. Results of d2 test showed statistically significant differences in the parameters of total number of errors and omission errors. In both the caffeinated and decaffeinated groups, the patients showed slight increase in VAS score and nasal cavity area; however, the difference was not statistically significant. Also, caffeinated coffee intake compared to decaffeinated coffee intake showed no significant relevance to olfactory function. Conclusion.: Caffeine may significantly improve attentional congnitive function, while not have acute effects on olfactory function.
... The total number of participants included in each study ranged from 7 to 30 people. Data obtained included 9 studies with 22 data sets on glucose, 20,21,[23][24][25]28,34,35,37 11 studies with 18 data sets on ISI, 22,[26][27][28][29][30][31][32][33]36,38 and 5 studies with 8 data sets on insulin levels. 20,21,24,28,37 The characteristics of the included studies in the meta-analysis are presented in Tables 1-3. ...
Article
2Highlights:Pooled analysis revealed that acute caffeine supplementation, as pure caffeineor caffeinated coffee, increases glucose concentration and decreases ISI.In subgroup analysis significantly increased serum glucose levels only was seen in dose ≥250 mg of caffeine ingestion.In subgroup analysis for insulin sensitivity index (ISI), only pure caffeine was found to reduce ISI, not caffeinated coffee.Following acute caffeine supplementation, no significant effectwas found on insulin levels.AbstractBackground:Dueto the inconsistent results of previous studies on the acute impacts of coffee consumption on glycemic indices, this meta-analysis was accomplished to evaluate the acute effects ofcaffeineand caffeinated coffee on insulin sensitivity index (ISI) and serum levels of glucose and insulin in people with and without type 2 diabetes.Methods:PubMed and EMBASE were systematically searched for all English Randomized ControlledTrialstudies published up to January2019. Weighted mean difference (WMD)with 95% confidence interval (CI) wasreported as a measure of caffeine effects onglycemic indices. Cochran’s Q test and I2were applied to assess the between-study variance. Subgroup analysis was performedto assessthe possible sources of heterogeneity.Results:In total, 18 trials with a total of 252 participants were enrolled in the meta-analysis. The pooled analysis revealed that caffeine supplementation, as pure caffeineorcaffeinated coffee,increasesglucose concentration (WMD=2.48, 95%CI: 0.75 to 4.20; P = 0.005) and decreasesISI ACCEPTED MANUSCRIPT 3(WMD= -0.46; 95% CI: -0.86 to-0.07;P-value = 0.003), while, no significant effect was found oninsulin levels(WMD= 0.03,95%CI: -0.84 to 0.89),with evidence of significant heterogeneityfor analyses.In subgroup analysis, bothcaffeineand caffeinated coffee significantly increased serum glucoselevels; however, this effect was significant for dose ≥250 mgof caffeine ingestion. For ISI, only pure caffeinewas found to reduce ISI, not caffeinated coffee.Conclusions:Caffeine intake may acutely increase glucose concentration and decrease insulin sensitivity index. Caffeine hadnosignificanteffecton insulin levels.Keywords:Caffeine; Coffee; Insulin sensitivity index; Serum glucose;meta-analysis.
... Changes in perceptual processing could be the basis of changes in conceptual processing (Mesulam, 1990;Van Dantzig et al., 2008). The activation of fronto-parietal areas could be a part of the network associated with the observed perceptual and reading enhancements (Serra-Grabulosa et al., 2010). ...
Article
Background Reading is a unique human skill. Several brain networks involved in this complex skill mainly involve the left hemisphere language areas. Nevertheless, nonlinguistic networks found in the right hemisphere also seem to be involved in sentence and text reading. These areas do not deal with phonological information, but are involved in verbal and nonverbal pattern information processing. The right hemisphere is responsible for global processing of a scene, which is needed for developing reading skills. Aims Caffeine seems to affect global pattern processing specifically. Consequently, our aim was to discover if it could enhance text reading skill. Methods In two mechanistic studies ( n=24 and n=53), we tested several reading skills, global and local perception, alerting, spatial attention and executive functions, as well as rapid automatised naming and phonological memory, using a double-blind, within-subjects, repeated-measures design in typical young adult readers. Results A single dose of 200 mg caffeine improved global processing, without any effect on local information processing, alerting, spatial attention and executive or phonological functions. This improvement in global processing was accompanied by faster text reading speed of meaningful sentences, whereas single word/pseudoword or pseudoword text reading abilities were not affected. These effects of caffeine on reading ability were enhanced by mild sleep deprivation. Conclusions These findings show that a small quantity of caffeine could improve global processing and text reading skills in adults.
... Subjects with chronic disorders, nervous system disorders, those under chronic medication, history of mental illness, or regular alcohol consumers, were excluded from the study. Participants were required to avoid caffeine intake for a minimum of 12 h prior to the start of the fMRI session, as caffeine influences performance [20] and BOLD signal [21]. The study was approved by the ethics committee of the Hospital Clínic de Barcelona. ...
Article
Introduction: One of the most used paradigms in the study of attention is the Continuous Performance Test (CPT). The identical pairs version (CPT-IP) has been widely used to evaluate attention deficits in developmental, neurological and psychiatric disorders. However, the specific locations and the relative distribution of brain activation in networks identified with functional imaging, varies significantly with differences in task design. Aim: To design a task to evaluate sustained attention using functional magnetic resonance imaging (fMRI), and thus to provide data for research concerned with the role of these functions. Subjects and methods: Forty right-handed, healthy students (50% women; age range: 18-25 years) were recruited. A CPT-IP implemented as a block design was used to assess sustained attention during the fMRI session. Results: The behavioural results from the CPT-IP task showed a good performance in all subjects, higher than 80% of hits. fMRI results showed that the used CPT-IP task activates a network of frontal, parietal and occipital areas, and that these are related to executive and attentional functions. Conclusions: In relation to the use of the CPT to study of attention and working memory, this task provides normative data in healthy adults, and it could be useful to evaluate disorders which have attentional and working memory deficits.
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This chapter examines the failure of police, attorneys, judges, and juries to appreciate the magnitude of acute impairments of will and cognition in interrogation. The authors explore sources of enhanced susceptibility to interrogative influence triggered by the nature of the suspect’s immediate circumstances, rather than by chronic personal characteristics, which they call “acute interrogative suggestibility.” The authors consider the role of “interrogation-related regulatory decline” or IRRD in producing acute interrogative suggestibility -- that is, the decline in self-regulation resources necessary to control thinking and behavior in service of resisting interrogative influence. In particular, the authors concentrate on three common but underappreciated sources of IRRD in police interrogation, one or more of which are present in most cases involving claims of involuntary or false confession: acute emotional distress, fatigue and sleep deprivation, and glucose depletion. The chapter concludes by arguing that much more weight should be given to issues of acute sources of vulnerability to influence and suggestion than is presently the case.
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Energy drinks containing caffeine, taurine, and glucose may improve mood and cognitive performance. However, there are no studies assessing the individual and interactive effects of these ingredients. We evaluated the effects of caffeine, taurine, and glucose alone and in combination on cognitive performance and mood in 24-hour caffeine-abstained habitual caffeine consumers. Using a randomized, double-blind, mixed design, 48 habitual caffeine consumers (18 male, 30 female) who were 24-hour caffeine deprived received one of four treatments (200 mg caffeine/0 mg taurine, 0 mg caffeine/2000 mg taurine, 200 mg caffeine/2000 mg taurine, 0 mg caffeine/0 mg taurine), on each of four separate days, separated by a 3-day wash-out period. Between-participants treatment was a glucose drink (50 g glucose, placebo). Salivary cortisol, mood and heart rate were measured. An attention task was administered 30-minutes post-treatment, followed by a working memory and reaction time task 60-minutes post-treatment. Caffeine enhanced executive control and working memory, and reduced simple and choice reaction time. Taurine increased choice reaction time but reduced reaction time in the working memory tasks. Glucose alone slowed choice reaction time. Glucose in combination with caffeine, enhanced object working memory and in combination with taurine, enhanced orienting attention. Limited glucose effects may reflect low task difficulty relative to subjects' cognitive ability. Caffeine reduced feelings of fatigue and increased tension and vigor. Taurine reversed the effects of caffeine on vigor and caffeine-withdrawal symptoms. No effects were found for salivary cortisol or heart rate. Caffeine, not taurine or glucose, is likely responsible for reported changes in cognitive performance following consumption of energy drinks, especially in caffeine-withdrawn habitual caffeine consumers.
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One problem of fMRI images is that they include some noise coming from many other sources like the heart beat, breathing and head motion artifacts. All these sources degrade the data and can cause wrong results in the statistical analysis. In order to reduce as much as possible the amount of noise and to improve signal detection, the fMRI data is spatially smoothed prior to the analysis. The most common and standardized method to do this task is by using a Gaussian filter. The principal problem of this method is that some regions may be under-smoothed, while others may be over-smoothed. This is caused by the fact that the extent of smoothing is chosen independently of the data and is assumed to be equal across the image. To avoid these problems, we suggest in our work to use an adaptive Wiener filter which smooths the images adaptively, performing a little smoothing where variance is large and more smoothing where the variance is small. In general, the results that we obtained with the adaptive filter are better than those obtained with the Gaussian kernel. In this paper we compare the effects of the smoothing with a Gaussian kernel and with an adaptive Wiener filter, in order to demonstrate the benefits of the proposed approach.
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Functional magnetic resonance imaging (fMRI) is a technique to map the brain, anatomically as well as physiologically, which does not require any invasive analysis. In order to obtain brain activation maps, the subject under study must perform a task or be exposed to an external stimulus. At the same time a large amount of images are acquired using ultra-fast sequences through magnetic resonance. Afterwards, these images are processed and analyzed with statistical algorithms. This study was made in collaboration with the consolidated Neuropsychology Research Group of the University of Barcelona, focusing on applications of fMRI for the study of brain function in images obtained with various subjects. This group performed a study which analyzed fMRI data, acquired with various subjects, using the General Linear Model (GLM). The aim of our work was to analyze the same fMRI data using Independent Component Analysis (ICA) and compare the results with those obtained through GLM. Results showed that ICA was able to find more active networks than GLM. The activations were found in frontal, parietal, occipital and temporal areas.
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Rationale Benzodiazepines are useful and commonly prescribed. Unfortunately, they are associated with subtle but functionally significant neurocognitive side effects that increase the risk of motor vehicle accidents and falls. Objective The objective of this study was to determine whether clinically feasible measures of simple reaction time and reaction accuracy are sensitive to a single dose of lorazepam. Methods Using a randomized, double-blind, crossover design, 26 healthy adults (13 women; age = 26.9 ± 8.2 yr) were given 1.0 mg lorazepam or placebo 90 minutes prior to two data collection sessions. Participants completed simple and reaction accuracy tasks using a standardized “ruler drop” testing paradigm during each session. Outcomes were mean and variability of simple reaction time and reaction accuracy, which evaluates a participant’s ability to catch the device solely on the random 50% of trials that lights affixed to it illuminate on release. Reaction accuracy requires a go/no-go decision within 420 ms before the falling device strikes the floor. Results As compared with placebo, lorazepam increased simple reaction time variability (range = 43 ± 18 vs. 60 ± 23 ms, respectively; p = 0.004 and standard deviation = 14.6 ± 5.7 vs. 19.7 ± 7.3 ms, respectively; = 0.006) and decreased reaction accuracy (90 ± 7% vs. 84 ± 11%, respectively; p = 0.010). Conclusion Given prior work demonstrating associations between simple reaction time and reaction accuracy and functional outcomes such as self-protection, response to perturbations, and fall risk, these clinically available measures may have a role in identifying subtle, functionally significant cognitive changes related to short-term benzodiazepine use.
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The effect of caffeine as a cognitive enhancer is well known; however, caffeine-induced changes in the cortical regions are still not very clear. Therefore, in this study, we conducted an investigation of the activation and deactivation with blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) and of metabolic activity change with positron emission tomography (PET) in the human brain. Fourteen healthy subjects performed a visuomotor task inducing attention with 3 T MRI, and PET imaging was also carried out in seven subjects to determine the cerebral glucose metabolic changes of caffeine at rest. The result by fMRI showed that increased BOLD activation in the left cerebellum, putamen, insula, thalamus and the right primary motor cortex, and that decreased BOLD deactivation in the posterior medial and the left posterior lateral cortex. Also, the resting state PET data showed reduced metabolic activity in the putamen, caudate nucleus, insula, pallidum and posterior medial cortex. The common cortical regions between fMRI and PET, such as putamen, insula and posterior medial cortex, where significant changes occurred after caffeine ingestion, are well known to play an important role in cognitive function like attention. This result suggests that the effect of caffeine as a cognitive enhancer is derived by modulating the attentional areas.
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Background: Exercise improves cognition, but whether fitness status and caffeine modulate this effect remains unclear. Purpose: To determine if sustained attention is improved following exercise with and without caffeine in endurance-trained vs. sedentary adults. Methods: A continuous performance task (CPT), that is, a 20 min measure of sustained attention to assess accuracy and precision, was used to induce mental fatigue. Following the 20 min CPT, trained (n = 12) and sedentary (n = 12) participants completed either 30-min rest or 30-min moderate-intensity cycling below lactate threshold. Exercise trials were completed with placebo and caffeine (3 mg/kg) followed by cycling to volitional fatigue. Results: Exercise, as compared to rest, improved (p
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Sleep deprivation affects performance outcomes across a wide range of cognitive domains. Sleepiness and fatigue, caused by sleep loss, extended work and wakefulness, circadian misalignment, and sleep disorders are major causes of workplace human errors, incidents, and accidents. Car crashes related to falling asleep represent up to 20 % of all traffic accidents in industrial societies and are known to be more likely to cause death and severe injury. Sleep-related accidents are substantial in terms of personal injury, of property damage, lost productivity, and death. Management and prevention of sleep-related accidents should be a priority for the public, labor, governments, and industries. Scientific data on potentially useful countermeasures are needed.
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Background Black Tea is a widely consumed drink in the world. Evidence suggest Black Tea has stimulatory effect on humans. We investigated the effect of Black Tea on cognition using a cognitive test battery. Methods Participants (n = 32) were fasted overnight for 10 h and restrained from caffeine and other stimulant drugs for 14 days prior to participation. We randomly assigned participants into either an experimental (n = 16) or a control (n = 16) group. Experimental group consumed 250 ml of Black Tea (BT) while control group was received equal volume of water (W). Participants were tested on the following cognitive tasks: executive function, sustained attention, memory (memory span, immediate, delayed, working memory) and arithmetic calculation task. Results We found that BT group performed significantly (p < 0.05) faster in the executive function task (BT: M = 1671, SD = 319; W: M = 1935, SD = 372); simple reaction time task (BT: M = 333, SD = 87; W: M = 361, SD = 101), identification of target location in the visual search task (BT: M = 925, SD = 50; W: M = 972, SD = 115). We also showed that BT group forgotten significantly (p < 0.05) lower number of words in the delayed memory recall test (BT: M = 1.12, SD = 0.15; W: M = 1.37, SD = 0.33) and made significantly (p < 0.05) fewer errors in the trail making task (BT: M = 0.31, SD = 1.01; W: M = 1.31, SD = 1.66). Conclusions BT consumption speeded the performance, improved memory, reduced number of errors in the various cognitive tasks. Our results further showed that even in small volume of BT consumption can speed up cognitive processing.
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Some previous studies have demonstrated an early effect of caffeine administration on subjective state, but none of them has explored its existence after the administration of decaffeinated coffee, or the possible differences depending on the gender and circadian typology of the subjects. The aim of the present work is to investigate the early effects (10-30 min post-consumption) of a single low dose of caffeine (100 mg) and decaffeinated coffee on sleepiness, subjective activation and affect using a realistic design. The influence of gender and circadian typology is also explored. A randomized double-blind informed placebo controlled procedure was applied to 688 healthy undergraduate volunteers, mean age 22.03+/-2.21 years, 238 men and 450 women. Measures were recorded before and after beverage consumption (10, 20 and 30 min), in two experimental sessions: morning 11:00-13:00 h or afternoon 16:00-18:00 h. Caffeine administration induced arousing effects (lesser somnolence and greater activation) in all post-consumption records, while the effects of decaffeinated drink were only apparent at 10 min. Caffeine effects were greater in men, and the decaffeinated beverage produced greater effects in women. Circadian typology only showed effects for time of day (morning/afternoon) related with rhythmic expression. Future works should study more accurately the early effect of coffee beverages and the influence of gender, using other parameters which have proven to be sensitive to their administration. The effect of several caffeine doses should also be studied.
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Neuroimaging studies of normal subjects and studies of patients with focal lesions implicate regions of parietal cortex in verbal working memory (VWM), yet the precise role of parietal cortex in VWM remains unclear. Some evidence (; ) suggests that the parietal cortex mediates the storage of verbal information, but these studies and most previous ones included encoding and retrieval processes as well as storage and rehearsal of verbal information. A recent positron emission tomography (PET) study by isolated storage and rehearsal from other VWM processes and did not find reliable activation in parietal cortex. This result suggests that parietal cortex may not be involved in VWM storage, contrary to previous proposals. However, we report two behavioral studies indicating that some of the verbal material used by may not have required phonological representations in VWM. In addition, we report a PET study that isolated VWM encoding, retrieval, and storage and rehearsal processes in different PET scans and used material likely to require phonological codes in VWM. After subtraction of appropriate controls, the encoding condition revealed no reliable activations; the retrieval condition revealed reliable activations in dorsolateral prefrontal, anterior cingulate, posterior parietal, and extrastriate cortices, and the storage condition revealed reliable activations in dorsolateral prefrontal, inferior frontal, premotor, and posterior parietal cortices, as well as cerebellum. These results suggest that parietal regions are part of a network of brain areas that mediate the short-term storage and retrieval of phonologically coded verbal material.
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It is known that glucose administration is capable of improving performance on tests of declarative verbal memory and non-mnemonic tasks requiring high "mental effort". At the same time, cognitively demanding tasks are associated with elevated heart rate, a response that could feasibly be part of a physiological mechanism serving to increase the delivery of glucose to active brain substrates. The present placebo-controlled, double-blind, balanced, crossover study examined the interaction between glucose administration, cognitive performance and heart rate during three tasks of differing mental demand and somatically-matched control tasks. The effects of a glucose drink on participants' performance on two serial subtraction tasks (Serial Threes and Serial Sevens) and a Word Retrieval (Verbal Fluency) task were assessed. Heart rates were monitored throughout the experiment, and participants rated each task in terms of its perceived mental demand. Serial Sevens was rated as the most mentally demanding task, followed by Word Retrieval, then Serial Threes. Glucose consumption significantly improved performance on Serial Sevens, with a trend for improved performance on Word Retrieval. Both Serial Sevens and Serial Threes were associated with significant heart rate elevation above that seen in somatically matched control tasks (ruling out the possibility that accelerated heart rate was due to peripheral mechanisms alone). Unexpectedly, participants in the glucose condition had higher heart rates during cognitive processing. Additionally, individuals whose baseline heart rates were below the median performed better on Serial Threes and Serial Sevens. We suggest that supplemental glucose preferentially targets tasks with a relatively high cognitive load, which itself (through unknown mechanisms) mobilises physiological reserves as part of a natural response to such tasks. Furthermore, baseline heart rate and responses to cognitive demand and glucose administration may represent important physiological individual differences.
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Memory for a list of 20 words can be enhanced by preceding learning by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution (Psychopharmacology 137 (1998) 259; Psychopharmacology 157 (2001) 46). However, using this anterograde administration procedure, it is impossible to separate whether glucose affects encoding, consolidation, or retrieval. The present placebo-controlled, double-blind study investigated the effect of anterograde and retrograde administration on memory performance in healthy young participants. In order to evaluate whether post-acquisition administration of glucose can improve memory performance and to compare possible differences in the size of the effect, participants were administered 25 g of glucose immediately before or immediately after presentation of a word list. Moreover, in order to investigate whether the effect of glucose administration on memory performance is time-dependent, a third group received 25 g of glucose 15 min before learning the word list. Word- list recall was tested 30 min and 24 h after word list presentation. Measures of spatial memory performance and working memory were also evaluated. The results of this study showed that both pre- and post-acquisition oral glucose administration (25 g) can improve memory performance. However, as the time interval between anterograde glucose administration and memory encoding increased, the glucose memory facilitation effect decreased. This study provides evidence that glucose enhances memory performance in healthy young people even when it is given after learning has taken place, and that this effect is observed at least up to 24 h after glucose administration. Moreover, it provides evidence that the effect of glucose on memory performance may be time-dependent, as the enhancement of retention was decreased when the administration-learning interval was increased.
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The literature suggests that the following effects on behavior of adult humans may occur when individuals consume moderate amounts of caffeine. (1) Caffeine increases alertness and reduces fatigue. This may be especially important in low arousal situations (e.g. working at night). (2) Caffeine improves performance on vigilance tasks and simple tasks that require sustained response. Again, these effects are often clearest when alertness is reduced, although there is evidence that benefits may still occur when the person is unimpaired. (3) Effects on more complex tasks are difficult to assess and probably involve interactions between the caffeine and other variables which increase alertness (e.g. personality and time of day). (4) In contrast to the effects of caffeine consumption, withdrawal of caffeine has few effects on performance. There is often an increase in negative mood following withdrawal of caffeine, but such effects may largely reflect the expectancies of the volunteers and the failure to conduct "blind" studies. (5) Regular caffeine usage appears to be beneficial, with higher users having better mental functioning. (6) Most people are very good at controlling their caffeine consumption to maximise the above positive effects. For example, the pattern of consumption over the day shows that caffeine is often consumed to increase alertness. Indeed, many people do not consume much caffeine later in the day since it is important not to be alert when one goes to sleep. In contrast to effects found from normal caffeine intake, there are reports that have demonstrated negative effects when very large amounts are given or sensitive groups (e.g. patients with anxiety disorders) were studied. In this context caffeine has been shown to increase anxiety and impair sleep. There is also some evidence that fine motor control may be impaired as a function of the increase in anxiety. Overall, the global picture that emerges depends on whether one focuses on effects that are likely to be present when caffeine is consumed in moderation by the majority of the population or on the effects found in extreme conditions. The evidence clearly shows that levels of caffeine consumed by most people have largely positive effects on behavior. Excessive consumption can lead to problems, especially in sensitive individuals.
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Recent interest has emerged in the use of pharmacologic methods to maximize blood oxygenation level-dependent (BOLD) signal intensity changes in functional MR imaging (fMRI). Adenosine antagonists, such as caffeine and theophylline, have been identified as potential agents for this purpose. The present study was designed to determine whether caffeine-induced decreases in cerebral perfusion result in enhanced BOLD responses to visual and auditory stimuli. MR imaging was used to measure resting cerebral perfusion and stimulus-induced BOLD signal intensity changes in 19 patients. We evaluated the relationship between resting cerebral perfusion and the magnitude of BOLD signal intensity induced by visual and auditory stimulation under caffeine and placebo conditions. The data showed that changes in resting cerebral perfusion produced by caffeine are not a consistent predictor of BOLD signal intensity magnitude. Although all cerebral perfusion was reduced in all study participants in response to caffeine, only 47% of the participants experienced BOLD signal intensity increase. This finding was independent of the participants' usual caffeine consumption. The data presented herein show that the relationship between resting cerebral perfusion and the magnitude of BOLD signal intensity is complex. It is not possible to consistently enhance BOLD signal intensity magnitude by decreasing resting perfusion with caffeine. Future studies aimed at evaluating the relationship between perfusion and BOLD signal intensity changes should seek a means to selectively modulate known components of the neural and vascular responses independently.
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The symptoms of bipolar disorder suggest dysfunction of anterior limbic networks that modulate emotional behavior and that reciprocally interact with dorsal attentional systems. Bipolar patients maintain a constant vulnerability to mood episodes even during euthymia, when symptoms are minimal. Consequently, we predicted that, compared with healthy subjects, bipolar patients would exhibit abnormal activation of regions of the anterior limbic network with corresponding abnormal activation of other cortical areas involved in attentional processing. In all, 10 unmedicated euthymic bipolar patients and 10 group-matched healthy subjects were studied with fMRI while performing the Continuous Performance Task-Identical Pairs version (CPT-IP). fMRI scans were obtained on a 3.0 T Bruker system using an echo planar imaging (EPI) pulse sequence, while subjects performed the CPT-IP and a control condition to contrast group differences in regional brain activation. The euthymic bipolar and healthy subjects performed similarly on the CPT-IP, yet showed significantly different patterns of brain activation. Specifically, bipolar patients exhibited increased activation of limbic, paralimbic, and ventrolateral prefrontal areas, as well as visual associational cortices. Healthy subjects exhibited relatively increased activation in fusiform gyrus and medial prefrontal cortex. In conclusion, these differences suggest that bipolar patients exhibit overactivation of anterior limbic areas with corresponding abnormal activation in visual associational cortical areas, permitting successful performance of an attentional task. Since the differences occurred in euthymia, they may represent trait, rather than state, abnormalities of brain function in bipolar disorder.
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Both glucose and caffeine can improve aspects of cognitive performance and, in the case of caffeine, mood. There are few studies investigating the effects of the two substances in combination. We assessed the mood, cognitive and physiological effects of a soft drink containing caffeine and glucose as well as flavouring levels of herbal extracts. The effects of different drink fractions were also evaluated. Using a randomised, double-blind, balanced, five-way crossover design, 20 participants who were overnight fasted and caffeine-deprived received 250 ml drinks containing 37.5 g glucose; 75 mg caffeine; ginseng and ginkgo biloba at flavouring levels; a whole drink (containing all these substances) or a placebo (vehicle). Participants were assessed in each drink condition, separated by a 7-day wash-out period. Cognitive, psychomotor and mood assessment took place immediately prior to the drink then 30 min thereafter. The primary outcome measures included five aspects of cognitive performance from the Cognitive Drug Research assessment battery. Mood, heart rate and blood glucose levels were also monitored. Compared with placebo, the whole drink resulted in significantly improved performance on "secondary memory" and "speed of attention" factors. There were no other cognitive or mood effects. This pattern of results would not be predicted from the effects of glucose and caffeine in isolation, either as seen here or from the literature addressing the effects of the substances in isolation. These data suggest that there is some degree of synergy between the cognition-modulating effects of glucose and caffeine which merits further investigation.
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Evidence for the behavioural effects of caffeine is prevalent in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. However, there is an on-going debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of caffeine withdrawal. Using participants who had consumed their normal daily quota of caffeine this study alleviated this potential confound as all participants were not withdrawn at the time of testing. To determine whether caffeine influenced the mood and performance of non-withdrawn volunteers. Sixty eight volunteers, all of whom were regular caffeine consumers, consumed their normal amount of caffeine over the course of the day. Baseline measures of mood and performance were then carried out followed by double-blind administration of caffeine (2 mg/kg) or placebo. The test battery was repeated again 30 min after ingestion of the drink. Our findings showed improvements comparable to previous research. Mood was improved and performance on a number of cognitive measures was improved. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems. This study provided evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative withdrawal effects.
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The cognitive and mood effects of caffeine are well documented. However, the majority of studies in this area involve caffeine-deprived, habitual caffeine users. It is therefore unclear whether any beneficial findings are due to the positive effects of caffeine or to the alleviation of caffeine withdrawal. The present placebo-controlled, double-blind, balanced crossover study investigated the acute cognitive and mood effects of caffeine in habitual users and habitual non-users of caffeine. Following overnight caffeine withdrawal, 24 habitual caffeine consumers (mean=217 mg/day) and 24 habitual non-consumers (20 mg/day) received a 150 ml drink containing either 75 or 150 mg of caffeine or a matching placebo, at intervals of > or =48 h. Cognitive and mood assessments were undertaken at baseline and 30 min post-drink. These included the Cognitive Drug Research computerised test battery, two serial subtraction tasks, a sentence verification task and subjective visual analogue mood scales. There were no baseline differences between the groups' mood or performance. Following caffeine, there were significant improvements in simple reaction time, digit vigilance reaction time, numeric working memory reaction time and sentence verification accuracy, irrespective of group. Self-rated mental fatigue was reduced and ratings of alertness were significantly improved by caffeine independent of group. There were also group effects for rapid visual information processing false alarms and spatial memory accuracy with habitual consumers outperforming non-consumers. There was a single significant interaction of group and treatment effects on jittery ratings. Separate analyses of each groups' responses to caffeine revealed overlapping but differential responses to caffeine. Caffeine tended to benefit consumers' mood more while improving performance more in the non-consumers. These results do not support a withdrawal alleviation model. Differences in the patterns of responses to caffeine by habitual consumers and habitual non-consumers may go some way to explaining why some individuals become caffeine consumers.
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The present study contrasted caffeine's effects on individuals who expect caffeine to stimulate them and those who do not. Secondly, whether a message that caffeine rather than placebo was administered would also affect these two groups of subjects differently was investigated. The study was conducted single-blind in a 2x2x2 mixed design. The between subjects factor was whether they expected caffeine to stimulate them (E+) or not (E-) according to their self reports obtained before the experiment began. The within subjects factors were message (told caffeine vs told placebo) and beverage type (given caffeine vs placebo). Sixteen subjects in each group (n=32) performed on signal detection, memory scanning and delayed free recall tasks following ingestion of either caffeinated or decaffeinated coffee on two sessions each, a total of four experimental sessions. On each session, subjects were given a message regarding their drink (told caffeine vs told placebo). However, on two sessions there was a mismatch between the message and drink given. For signal detection, performance under caffeine was better than placebo in the E+ but not the E- group. However, subjects in the E+ group did not benefit more than the E- group in either message condition. On memory scanning, detections and false alarms did not differ for either beverage, nor was there a differential finding in the E+ and E- groups. However, reaction time under caffeine condition was shorter. No effects of message were found. Caffeine and message also did not have any effect on performance on the delayed free recall task. The hypothesis that caffeine and message would affect E+ and E- subjects differentially was partly supported.
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It has been suggested that caffeine is most likely to benefit mood and performance when alertness is low. To measure the effects of caffeine on psychomotor and cognitive performance, mood, blood pressure and heart rate in sleep-restricted participants. To do this in a group of participants who had also been previously deprived of caffeine for 3 weeks, thereby potentially removing the confounding effects of acute caffeine withdrawal. Participants were moderate to moderate-high caffeine consumers who were provided with either decaffeinated tea and/or coffee for 3 weeks (LTW) or regular tea and/or coffee for 3 weeks (overnight caffeine-withdrawn participants, ONW). Then, following overnight caffeine abstinence, they were tested on a battery of tasks assessing mood, cognitive performance, etc. before and after receiving caffeine (1.2 mg/kg) or on another day after receiving placebo. Final analyses were based on 17 long-term caffeine-withdrawn participants (LTW) and 17 ONW participants whose salivary caffeine levels on each test day confirmed probable compliance with the instructions concerning restrictions on consumption of caffeine-containing drinks. Acute caffeine withdrawal (ONW) had a number of negative effects, including impairment of cognitive performance, increased headache, and reduced alertness and clear-headedness. Caffeine (versus placebo) did not significantly improve cognitive performance in LTW participants, although it prevented further deterioration of performance in ONW participants. Caffeine increased tapping speed (but tended to impair hand steadiness), increased blood pressure, and had some effects on mood in both groups. The findings provide strong support for the withdrawal reversal hypothesis. In particular, cognitive performance was found to be affected adversely by acute caffeine withdrawal and, even in the context of alertness lowered by sleep restriction, cognitive performance was not improved by caffeine in the absence of these withdrawal effects. Different patterns of effects (or lack of effects) of caffeine and caffeine withdrawal were found for other variables, but overall these results also suggest that there is little benefit to be gained from caffeine consumption.
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Although it is widely believed that caffeine can enhance human performance and mood, the validity of this belief has been questioned, giving rise to debate. The central question is whether superior performance and mood after caffeine represent net benefits, or whether differences between caffeine and control conditions are due to reversal of adverse withdrawal effects. To provide a focussed review of relevant experimental studies with the aim of clarifying current understanding regarding the effects of caffeine on human performance and mood. To avoid the shortcomings of standard placebo-controlled studies, which are ambiguous due to failure to control for the confounding influence of withdrawal reversal, three main experimental approaches have been employed: studies that compare consumers and low/non-consumers, pre-treatment and ad lib consumption studies, and long-term withdrawal studies. Of the three approaches, only long-term withdrawal studies are capable of unambiguously revealing the net effects of caffeine. Overall, there is little evidence of caffeine having beneficial effects on performance or mood under conditions of long-term caffeine use vs abstinence. Although modest acute effects may occur following initial use, tolerance to these effects appears to develop in the context of habitual use of the drug. Appropriately controlled studies show that the effects of caffeine on performance and mood, widely perceived to be net beneficial psychostimulant effects, are almost wholly attributable to reversal of adverse withdrawal effects associated with short periods of abstinence from the drug.
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Data on the development of the attentional systems remain scarce. We used structural and event-related functional magnetic resonance imaging to investigate differences in the neural mechanisms associated with alerting, reorienting, and executive control of attention between children (ages 8 to 12 years) and adults, while controlling for effects of performance and brain morphology. Behaviorally, children exhibited a numerically smaller alerting effect and significantly larger invalidity (reorienting) and interference (executive control of attention) effects. Neurally, children showed significantly reduced brain activation in a priori defined regions-of-interest in right-sided frontal-midbrain regions during alerting, in the right-sided temporo-parietal junction during reorienting of attention, and in the dorsolateral prefrontal cortex during executive control of attention. In addition, children activated significantly more brain regions outside the a priori defined regions-of-interest, such as the superior frontal gyrus during reorienting and the superior temporal gyrus during executive control of attention. Functional group differences overlapped with structural group differences in gray matter volume in particular within the frontopolar areas. The data suggest that there is a transition from functional yet immature systems supporting attentional functions in children to the more definitive adult networks and that the differences observed may reflect both developmental changes in cognitive strategies and morphology.
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Evidence for behavioural effects of caffeine is well documented in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. These effects are most prominent in low arousal situations. However, there is an ongoing debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of a period of caffeine withdrawal (e.g. overnight abstinence). To avoid such a confound this study included multiple doses of caffeine which were administered under double-blind conditions to participants who had ingested their normal daily quota of caffeine. In the present study participants were fatigued by carrying out a prolonged testing schedule in the evening. Sixty volunteers, all regular caffeine consumers, took part in the study. They attended for three sessions on separate days. They were instructed to consume normal amounts of caffeinated beverages. Consumption was measured by a diary and saliva samples were taken and caffeine assays conducted. A baseline test session was carried out at 18.00h and following this a double blind placebo controlled caffeine challenge (1.5mg/kg) conducted. The test battery was repeated twice approximately 30 minutes after the caffeine challenge. Following this another drink was administered and the test battery repeated twice more. On one test session volunteers had placebo in both drinks, in another they had caffeine in both drinks and another caffeine in the first and placebo in the second. Order of conditions was balanced across subjects. The results showed that caffeine led to a more positive mood and improved performance on a number of tasks. Different effects of caffeine were seen depending on the person's level of arousal. Linear effects of caffeine dose were also observed. This is evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative effects of a long period of caffeine abstinence. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems.
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The ingestion of a glucose-containing drink has been shown to improve cognitive performance, particularly memory functioning. However, it remains unclear as to the extent to which task domain and task difficulty moderate the glucose enhancement effect. The aim of this research was to determine whether boosts in performance are restricted to particular classes of memory (episodic v. semantic) or to tasks of considerable cognitive load. A repeated measures (25 g glucose v. saccharin), counterbalanced, double-blind design was used with younger and older adults. Participants performed a battery of episodic (e.g. paired associate learning) and semantic memory (e.g. category verification) tasks under low and high cognitive load. Electrophysiological measures (heart rate and galvanic skin response) of arousal and mental effort were also gathered. The results indicated that whilst glucose appeared to aid episodic remembering, cognitive load did not exaggerate the facilitative effect. For semantic memory, there was little evidence to suggest that glucose can boost semantic memory retrieval even when the load was manipulated. One exception was that glucose facilitated performance during the difficult category fluency task. Regardless, the present findings are consistent with the domain-specific account in which glucose acts primarily on the hippocampal region, which is known to support episodic memory. The possible contribution of the hippocampus in semantic memory processing is also discussed.
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Previous research has consistently found enhancement of memory after the ingestion of a glucose containing drink. The aims of the present study were to specify more precisely the nature of this facilitation by examining the cognitive demand hypothesis. This hypothesis predicts greater glucose induced facilitation on tasks that require significant mental effort. In two experiments, both employing an unrelated sample design, participants consumed either 25 g of glucose or a control solution. In experiment 1, participants first studied low and high imagery word-pairs and memory was assessed 1-, 7- and 14-days later by cued recall. Overall, glucose enhanced both encoding and consolidation processes only for the more difficult low imagery pairs. In experiment 2, the degree of mental effort in a verbal memory task was manipulated in two ways: (1) by varying the phonological similarity of the words; and (2) by varying the length of word lists. Glucose was found to enhance memory only for longer word lists. These data are consistent with the idea that glucose is especially effective in demanding memory tasks, but place some limits on the forms of difficulty that are susceptible to enhancement.
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A review of the literature pertaining to the neurobehavioral pharmacology of abusable drugs, this is the only book to survey each of the eleven classes of addictive drugs from the perspectives of neurological, behavioral, and clinical pharmacology. Designed to serve as a companion text to the DSM-IV manual, the Handbook provides comprehensive information about each drug and drug class having abuse potential with respect to their pharmaceutical mechanisms and actions.
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Memory for a list of 20 words can be enhanced by preceding learning by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution (Psychopharmacology 137 (1998) 259; Psychopharmacology 157 (2001) 46). However, using this anterograde administration procedure, it is impossible to separate whether glucose affects encoding, consolidation, or retrieval. The present placebo-controlled, double-blind study investigated the effect of anterograde and retrograde administration on memory performance in healthy young participants. In order to evaluate whether post-acquisition administration of glucose can improve memory performance and to compare possible differences in the size of the effect, participants were administered 25 g of glucose immediately before or immediately after presentation of a word list. Moreover, in order to investigate whether the effect of glucose administration on memory performance is time-dependant, a third group received 25 g of glucose 15 min before learning the word list. Word- list recall was tested 30 min and 24 h after word list presentation. Measures of spatial memory performance and working memory were also evaluated. The results of this study showed that both pre- and post- acquisition oral glucose administration (25 g) can improve memory performance. However, as the time interval between anterograde glucose administration and memory encoding increased, the glucose memory facilitation effect decreased. This study provides evidence that glucose enhances memory performance in healthy young people even when it is given after learning has taken place, and that this effect is observed at least up to 24 h after glucose administration. Moreover, it provides evidence that the effect of glucose on memory performance may be time-dependent, as the enhancement of retention was decreased when the administration- learning interval was increased. # 2002 Elsevier Science B.V. All rights reserved.
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Statistical parametric maps are spatially extended statistical processes that are used to test hypotheses about regionally specific effects in neuroimaging data. The most established sorts of statistical parametric maps (e.g., Friston et al. [1991]: J Cereb Blood Flow Metab 11:690–699; Worsley et al. [1992]: J Cereb Blood Flow Metab 12:900–918) are based on linear models, for example ANCOVA, correlation coefficients and t tests. In the sense that these examples are all special cases of the general linear model it should be possible to implement them (and many others) within a unified framework. We present here a general approach that accomodates most forms of experimental layout and ensuing analysis (designed experiments with fixed effects for factors, covariates and interaction of factors). This approach brings together two well established bodies of theory (the general linear model and the theory of Gaussian fields) to provide a complete and simple framework for the analysis of imaging data. The importance of this framework is twofold: (i) Conceptual and mathematical simplicity, in that the same small number of operational equations is used irrespective of the complexity of the experiment or nature of the statistical model and (ii) the generality of the framework provides for great latitude in experimental design and analysis.
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To study the effects of consuming caffeine and glucose, alone and combined, on cognitive performance. Seventy-two healthy subjects (36 women; age range 18-25) were tested early in the morning, having fasted overnight. Using a double-blind, randomised design, subjects received one of the following beverages: water (150 ml); water plus 75 mg of caffeine; water plus 75 g of glucose; water plus and 75 mg of caffeine and 75 g of glucose. Attention, manual dexterity, visuo-spatial and frontal functions, memory (immediate, consolidation and working) and subjective state were all assessed. The combination of caffeine and glucose had beneficial effects on attention (sequential reaction time tasks) and on learning and consolidation of verbal memory, effects not being observed when either substance was administered alone. Caffeine only showed improvement in simple reaction time and glucose in simple and one sequential reaction time tasks and in the manual dexterity assembly task. The results indicate that the synergistic effects of caffeine and glucose can benefit sustained attention and verbal memory, even with adequate levels of activation of the subjects. However, further studies are required, controlling for different levels of cognitive effort and also considering measurements of neural activity.
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Caffeine is a commonly used neurostimulant that also produces cerebral vasoconstriction by antagonizing adenosine receptors. Chronic caffeine use results in an adaptation of the vascular adenosine receptor system presumably to compensate for the vasoconstrictive effects of caffeine. We investigated the effects of caffeine on cerebral blood flow (CBF) in increasing levels of chronic caffeine use. Low (mean = 45 mg/day), moderate (mean = 405 mg/day), and high (mean = 950 mg/day) caffeine users underwent quantitative perfusion magnetic resonance imaging on four separate occasions: twice in a caffeine abstinent state (abstained state) and twice in a caffeinated state following their normal caffeine use (native state). In each state, there were two drug conditions: participants received either caffeine (250 mg) or placebo. Gray matter CBF was tested with repeated-measures analysis of variance using caffeine use as a between-subjects factor, and correlational analyses were conducted between CBF and caffeine use. Caffeine reduced CBF by an average of 27% across both caffeine states. In the abstained placebo condition, moderate and high users had similarly greater CBF than low users; but in the native placebo condition, the high users had a trend towards less CBF than the low and moderate users. Our results suggest a limited ability of the cerebrovascular adenosine system to compensate for high amounts of daily caffeine use.
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This review focuses on the neurologic issues concerning the treatment of hypo- or hyperglycemia in the critically ill patient. Articles written in English and identified through the Bibliographic Retrieved Service Colleague database. Articles chosen on the basis of their relevance to the issue of blood glucose management and its neurologic effects in critically ill patients. Data from articles were analyzed to obtain a scientific foundation and rationale for treating abnormal blood glucose levels. Moderate hypoglycemia may evoke a significant stress response, behavioral changes, and alterations in cerebral blood flow and metabolism. It is unclear what effect prolonged or repeated episodes of moderate hypoglycemia may have on patient outcome. However, alterations in cerebral vascular physiology must be addressed when caring for patients with cerebral ischemia or intracranial compliance problems. Depending on its severity, hypoglycemia has varying influences on neurologic damage after ischemia. Hyperglycemia may impair neuronal recovery following cerebral ischemia. However, the detrimental effects of hyperglycemia vary depending on the types of brain ischemia sustained (focal or global). Evidence suggests that hyperglycemia during global and incomplete global ischemia events is detrimental to neurologic outcome. However, the relationship between hyperglycemia and outcome after focal ischemia is controversial. Because both hypo- and hyperglycemia may produce neurologic changes, aggressive management of abnormal glucose values is warranted.
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Positron emission tomographic (PET) studies of human attention have begun to dissect isolable components of this complex higher brain function, including a midline attentional system in a region of the anterior cingulate cortex. The right hemisphere may play a special part in human attention; neglect, an important phenomenon associated with damage to attentional systems, is more severe, extensive and long-lasting after lesions to the right hemisphere. Here we use PET measurements of brain blood flow in healthy subjects to identify changes in regional brain activity during simple visual and somatosensory tasks of sustained attention or vigilance. We find localized increases in blood flow in the prefrontal and superior parietal cortex primarily in the right hemisphere, regardless of the modality or laterality of sensory input. The anterior cingulate was not activated during either task. These data localize the vigilance aspects of normal human attention to sensory stimuli, thereby clarifying the biology underlying asymmetries of attention to such stimuli that have been reported in clinical lesions.
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The Continuous Performance Test-Identical Pairs version was administered to 14 schizophrenic patients, 17 depressed patients, and 28 normal controls. The task was divided into verbal and spatial stimuli, as well as no-distraction and distraction (verbal and auditory) conditions. Both patient groups displayed attentional impairments compared to normal subjects, but they differed from each other in specific profiles. Schizophrenic patients were characterized by a global impairment and a particular inability to focus on the critical stimuli, whether verbal or spatial. They also made an excess of random responses throughout the task but showed no evidence that attention declined from its initial level over time. Depressed patients did not display a global attentional deficit but did show a specific inability to attend to spatial as compared to verbal stimuli and, in particular, a confusion when the spatial stimuli were only slightly different. Performance on a secondary task in response to a change in expectation improved dramatically for depressed but not schizophrenic patients, suggesting a more efficient allocation strategy, a greater reserve of processing capacity, or more dependence on motivational factors in depressed patients. Schizophrenic and depressed patients were alike in extent of distractibility. Whereas normal controls improved with the onset of external distraction, schizophrenic and depressed patients deteriorated to an equal extent. Distractibility was thus concluded to be a correlate of acute psychiatric illness and not specific for schizophrenia.
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The rapid visual information processing (RVIP) task, a test of sustained attention which also requires working memory for its successful execution, has been used in a number of human psychopharmacological studies. Single digits are presented in quick succession (100 or 200 digits/min) on a computer screen, and target sequences of numbers must be detected with a button press. Although previous neuroimaging studies have implicated the frontal and parietal cortices in performance of simple sustained attention tasks, the neuroanatomical substrates of RVIP performance are not yet known. This information would prove invaluable in the interpretation of drug effects on this task, possibly delineating a neuronal network for neurotransmitter action. Therefore, this study investigated the functional anatomy of the RVIP task using positron emission tomography (PET) derived measures of regional cerebral blood flow (rCBF) in eight healthy volunteers. Subjects were required to perform variants of the RVIP task which manipulated both the level of working memory load and the speed of stimulus presentation. Compared with a rest condition (eyes closed), the RVIP task increased rCBF bilaterally in the inferior frontal gyri, parietal cortex and fusiform gyrus, and also in the right frontal superior gyrus rostrally. In comparison with a simple sustained attention control condition, the aforementioned right frontal activations were no longer apparent. We suggest that these data are consistent with the existence of a right fronto-parietal network for sustained, and possibly selective, attention, and a left fronto-parietal network for the phonological loop component of working memory.
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Recent research findings indicate that glucose administration enhances some aspects of cognitive functioning. To date, those studies which have investigated the effects of glucose on memory in human participants have concentrated on its apparent ability to attenuate memory impairment. Relatively little research has been done in humans investigating the effects of glucose on memory performance in young healthy participants in whom no memory deficits exist. Moreover, the work which has been conducted in this population has produced somewhat equivocal findings. In this study, after overnight fasting the influence of a 25 g oral dosage of glucose on a range of measures of memory performance was investigated in healthy young female participants. Two control treatments (saccharin and water) were also administered. There was a significant glucose facilitation effect upon performance of long-term verbal free and cued recall tasks which did not vary with test delay. Performance on these free and cued verbal recall measures correlated significantly with blood glucose levels across all participants. No glucose-related facilitation was observed on either a test of short-term verbal memory (forwards/backwards digit recall) or a test of long-term non-verbal memory (complex figure reproduction). However, the significant glucose-related effects observed with long-term free and cued recall remained after controlling for participants' differential baseline blood glucose levels and individual levels of immediate memory performance. Therefore, memory improvement after glucose ingestion was not merely a consequence of lower baseline blood glucose or lower immediate memory performance in the glucose treatment group. These findings indicate that there may be some fractionation in the memory facilitation effects of glucose: the memory enhancing effect of glucose administration in healthy young adults may be greatest on tests of long-term verbal recall. The results suggest that glucose may enhance retention in and/or retrieval from long-term verbal memory.
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A group of young adult females, who had or had not eaten breakfast, drank either a glucose drink or a placebo. Fasting was associated with poorer performance on the Brown-Petersen task, a test of memory. A glucose drink improved the memory of those who had fasted, although it did not influence those who had eaten breakfast. In those who had fasted, the glucose drink resulted in memory comparable to those who had consumed breakfast. Those with higher levels of blood glucose upon arrival in the laboratory had better memories. In those taking a glucose drink, after an initial rise, rapidly falling levels of blood glucose were associated with better memory.
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Neuroimaging has, in many respects, revolutionized the study of behavioral neurology and cognitive neuroscience. Early studies of brain-behavior relationships relied on a precise neurological examination as the basis for hypothesizing the site of brain damage that was responsible for a given behavioral syndrome. The advent of structural brain imaging, first with computed tomography (CT) and later with magnetic resonance imaging (MRI), paved the way for more precise anatomical localization of the cognitive deficits that are manifest after brain injury. In recent years, functional neuroimaging, broadly defined as techniques that provide measures of brain activity, has further increased our ability to study the neural basis of behavior. The modern era of functional brain imaging was introduced with the use of positron emission tomography (PET). In more recent years, functional magnetic resonance imaging (fMRI) has rapidly emerged as an extremely powerful technique with many advantages over PET for studying cognition. Thus, the principles underlying fMRI studies of cognition are the focus of this review.
Article
Electrophysiological studies suggest sensitivity of the prefrontal cortex to changes in the probability of an event. The purpose of this study was to determine if subregions of the prefrontal cortex respond differentially to changes in target probabilities using functional magnetic resonance imaging (fMRI). Ten right-handed adults were scanned using a gradient-echo, echo planar imaging sequence during performance of an oddball paradigm. Subjects were instructed to respond to any letter but "X". The frequency of targets (i.e., any letter but X) varied across trials. The results showed that dorsal prefrontal regions were active during infrequent events and ventral prefrontal regions were active during frequent events. Further, we observed an inverse relation between the dorsal and ventral prefrontal regions such that when activity in dorsal prefrontal regions increased, activity in ventral prefrontal regions decreased, and vice versa. This finding may index competing cognitive processes or capacity limitations. Most importantly, these findings taken as a whole suggest that any simple theory of prefrontal cortex function must take into account the sensitivity of this region to changes in target probability.
Article
An anatomical parcellation of the spatially normalized single-subject high-resolution T1 volume provided by the Montreal Neurological Institute (MNI) (D. L. Collins et al., 1998, Trans. Med. Imag. 17, 463-468) was performed. The MNI single-subject main sulci were first delineated and further used as landmarks for the 3D definition of 45 anatomical volumes of interest (AVOI) in each hemisphere. This procedure was performed using a dedicated software which allowed a 3D following of the sulci course on the edited brain. Regions of interest were then drawn manually with the same software every 2 mm on the axial slices of the high-resolution MNI single subject. The 90 AVOI were reconstructed and assigned a label. Using this parcellation method, three procedures to perform the automated anatomical labeling of functional studies are proposed: (1) labeling of an extremum defined by a set of coordinates, (2) percentage of voxels belonging to each of the AVOI intersected by a sphere centered by a set of coordinates, and (3) percentage of voxels belonging to each of the AVOI intersected by an activated cluster. An interface with the Statistical Parametric Mapping package (SPM, J. Ashburner and K. J. Friston, 1999, Hum. Brain Mapp. 7, 254-266) is provided as a freeware to researchers of the neuroimaging community. We believe that this tool is an improvement for the macroscopical labeling of activated area compared to labeling assessed using the Talairach atlas brain in which deformations are well known. However, this tool does not alleviate the need for more sophisticated labeling strategies based on anatomical or cytoarchitectonic probabilistic maps.
Article
This study explored the possible use of caffeine as an agent to improve the BOLD (blood oxygen level-dependent) signal response in fMRI. Previous research has demonstrated that caffeine has the ability to reset the level of coupling between blood flow and neuronal activity. In the present study, it has been shown that caffeine causes a decrease in cerebral perfusion by as much as 13.2% without a change in performance. Caffeine is a cerebral vasoconstrictor that causes an increase in the concentration of deoxyhemoglobin and thus a decrease in the BOLD baseline resting signal by 4.4%. During activation, the vasculature responds from below-normal baseline levels with a normal increase in blood flow and volume, resulting in an overall increase in the BOLD contrast. This increase can be as large as 22-37% during the performance of a visually cued motor task. The benefit of such a large increase in the BOLD contrast could be used to improve the image resolution, the acquisition scheme, or the task design of fMRI experiments. Caffeine has the potential to be used as a contrast booster for fMRI experiments.
Article
Caffeine is the most widely used stimulant in the world. The stimulant effects of caffeine are mediated through its antagonistic properties on neuronal adenosine receptors. In addition, caffeine blocks neurovascular adenosine receptors and decreases cerebral perfusion. Although the effects of caffeine on blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging measures are extremely important, there are few studies addressing this issue in the literature. Because chronic caffeine use causes an upregulation of adenosine receptors, the differential effects of caffeine in low and high users is of particular interest. The present study was designed to test the hypothesis that caffeine has differential effects on the BOLD signal in high and low caffeine users. We demonstrated that the BOLD signal change in visual cortex was significantly greater in high users than in low users in the presence of caffeine. In addition, the magnitude of the BOLD signal was significantly correlated with caffeine consumption. We propose that the outcome observed here was due to an upregulation of adenosine receptors in high users, resulting in differential contributions of the neural and vascular effects of adenosine in the two study populations.
Article
This experiment was conducted to examine the influence of a moderate dose of caffeine (4 mg/kg) on delayed memory, metamemory, and sustained attention. One hundred and forty-two volunteers ingested either caffeine or placebo during a study session which included three different memory tasks (free recall, cued recall, and recognition), and they made predictions of future memory performance. On day 2, participants again ingested either caffeine or placebo and completed memory tests. Sustained attention performance was measured on both days, and caffeine reliably improved hit rates and response latencies. A reliable drug-state interaction was detected only in the free recall test of memory. Caffeine did not affect the magnitude or accuracy of memory predictions, but there was some evidence that expectancies about caffeine were related to cognitive performance. Overall, caffeine's impact on memory and metamemory was not robust in this study. Copyright 2001 John Wiley & Sons, Ltd.
Article
There is evidence that caffeine increases alertness and reduces fatigue. This may be especially so in low arousal situations (e.g. working at night or for prolonged hours). Caffeine has also been found to improve performance on vigilance tasks and simple tasks requiring sustained response. Again, these effects are often clearest when alertness is reduced, although there is evidence that benefits may still occur when the individual is unimpaired. Most studies to date have investigated the behavioural effects of caffeine in laboratory experiments using artificial tasks. In the current study 3 mg/kg caffeine was found to improve steering accuracy in a 1 h simulated drive. Measures of mood and performance on a sustained attention task also showed the benefits of caffeine. These findings suggest that laboratory results reflect a general benefit of caffeine that may also be observed in real-life situations. Other evidence examining the effects of caffeine on performance efficiency over the working day has shown the benefits of caffeine consumption on measures of sustained attention and alertness. This study also provided evidence suggesting that caffeine is often consumed when alertness is low to maximise alertness and performance efficiency. The implications of these findings for road safety are also considered. Copyright 2001 John Wiley & Sons, Ltd.
Article
The extent to which the measured (and felt) psychostimulant effects of caffeine represent a real benefit of caffeine consumption or merely withdrawal reversal is unclear. Results showing positive psychostimulant effects of acute caffeine administration in habitual non-consumers of caffeine would provide evidence for a net benefit of caffeine unconfounded by withdrawal. To compare the mood, alerting, psychomotor and reinforcing effects of caffeine in caffeine non-consumers and acutely (overnight) withdrawn caffeine consumers. In experiment 1, these participants consumed two differently flavoured drinks, one containing 100 mg caffeine and the other containing no caffeine. Each drink was consumed on 4 separate days in semi-random order, and self-ratings of mood and alertness were completed before and after drink consumption. On day 9, both drinks contained 50 mg caffeine and drink preference (choice) and intake were assessed. In experiment 2, mood, alertness and performance on a long-duration simple reaction time task were assessed before and after administration of 100 mg or placebo in a single test session. Prior to receiving caffeine, the (overnight withdrawn) caffeine consumers were less alert and more tense than the non-consumers. Caffeine only had significant reinforcing, mood and psychomotor performance effects in the caffeine consumers. The reinforcing effect of caffeine was evident from an effect on drink intake, but drink choice was unaffected. Caffeine increased self-rated alertness of both caffeine consumers and non-consumers; however, for some of the non-consumers this was associated with a worsening of performance. These results support the hypothesis that the psychostimulant and related effects of caffeine are due largely to withdrawal reversal.
Article
Clozapine has been shown to improve verbal declarative memory and other cognitive functions in chronic schizophrenia. This raises the possibility that additional adjunctive manipulations might improve memory further. In this study, we hypothesized that glucose, which improves memory in a variety of conditions, including schizophrenia, would improve memory more than saccharin in a group of patients stabilized on clozapine. Twelve outpatients with schizophrenia who received treatment with clozapine participated in a double-blind, counterbalanced, crossover study. Subjects received beverages containing either glucose or saccharin on one occasion, and then the other beverage about a week later. Fifteen minutes after ingesting the beverage, subjects received a brief battery of neuropsychological tests to assess verbal declarative memory, attention, and executive functions. Blood glucose levels were assessed at baseline, and at 15 and 50 min after beverage ingestion. The main findings were that retention of a list of words was improved in the glucose condition, while performance on a complex test of sustained vigilance declined after glucose ingestion. These findings provide evidence that glucose improves declarative memory in patients with schizophrenia who were treated with clozapine, and underscore the possibility of developing effective protocols to reduce cognitive dysfunctions in the disorder. They also highlight the need to explore the extent to which glucose modulates nonmemory cognitive functions such as attention, and to understand more generally how glucose availability and regulation influence cognition.
Article
The memory-improving action of glucose has now been studied for almost 20 years and the study of this phenomenon has led to a number of important developments in the understanding of memory, brain physiology and pathological consequences of impaired glucose tolerance. Glucose improvement of memory appears to involve two optimal doses in animals (100 mg/kg and 2 g/kg) that may correspond to two physiological mechanisms underlying glucose effects on memory. In humans, there have been few dose-response studies so the existence of more than one effective dose in humans is uncertain. Many tasks are facilitated by glucose in humans but tasks that are difficult to master or involve divided attention are improved more readily that easier tasks. There are a number of hypotheses about the physiological bases of the memory-improving action of glucose. Peripheral glucose injections could alleviate localized deficits in extracellular glucose in the hippocampus. These localized deficits may be due to changes in glucose transporters in that structure. Because certain neurotransmitters such as acetylcholine are directly dependent on the glucose supply for their synthesis, glucose is thought to facilitate neurotransmitter synthesis under certain circumstances. However, these hypotheses cannot account for the specificity of the dose-response effect of glucose. A number of peripheral mechanisms have been proposed, including the possibility that glucose-sensitive neurons in the brain or in the periphery may serve as glucose sensors and eventually produce neural changes that would facilitate memory processing. These latter results could be of importance because the mechanisms they suggest appear to be dose-dependent, a crucial characteristic to explain the dose-dependent effects of glucose. There may be an advantage to develop hypotheses that include both peripheral and central actions of glucose. There is evidence that impaired glucose regulation is associated with impaired cognition, particularly episodic memory. This impairment is minimal in young people but increases in older people (65 years and over) where it may compound other aging processes leading to reduced brain function. A small number of studies showed that glucose improvement of memory is associated with poor glucose regulation although this may not be the case for diabetic patients. Results of a few studies also suggest that drug treatments that improve glucose regulation also produce cognitive improvement in diabetic patients.
Article
Effects of a combination of caffeine and glucose were assessed in two double-blind, placebo-controlled, cross-over studies during extended performance of cognitively demanding tasks. In the first study, 30 participants received two drinks containing carbohydrate and caffeine (68 g/38 mg; 68 g/46 mg, respectively) and a placebo drink, in counter-balanced order, on separate days. In the second study 26 participants received a drink containing 60 g of ca