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An N-of-1 Investigation into Stress-Related Hemodynamic Responses in the Prefrontal Cortex During the First Sleep Cycle
Abstract
It is well-known that stress affects sleep quality, suggesting abnormal brain activity during sleep when people are stressed. However, no study has examined where brain processes stress during sleep. This study aims to explore the associations between bedtime stress and the hemodynamics in the prefrontal cortex (PFC) during the first sleep cycle under free-living conditions. Stress biomarkers including salivary cortisol and secretory immunoglobulin A (sIgA) were measured using the SOMA Dual Analyte LFD test kits on the experiment nights between 22:00-23:00 to control the circadian oscillation of the stress-related hormones. Perceived stress level was rated on a 1-10 Likert scale right after the collection of the salivary samples. The hemodynamics of the pre-frontal cortex (PFC) was measured using a wearable functional near-infrared spectroscopy (fNIRS) device. Correlation analysis with statistical test was performed to examine the associations between different stress indicators and a set of time-domain and frequency-domain features derived from the hemodynamic responses. Significantly positive linear correlations were observed in the standard deviation, skewness, and kurtosis between the average concentration change of oxyhemoglobin and that of deoxyhemoglobin in the whole region of interest. Stress was found to correlate to the hemodynamics in the mid-DLPFC, the caudal-DLPFC, and the left RLPFC. The relationships between stress and these PFC subregions depends on the stress indicator adopted. Our finding provides supplementary support to the role of the PFC in processing stress. The preliminary results also shed light on the development of stress response markers in brain activity that can be measured with wearable brain-computer interface technologies.
... Wearable fNIRS has also been used to evaluate expertise and the effect of feedback in laparoscopy procedures, 11,24 deception, 25 stress processing during sleep, 26 and walking. 12,27 A range of studies have also sought to employ wearable fNIRS devices in the study of infants during naturalistic interactions and play. ...
Recent progress in optoelectronics has made wearable and high-density functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) technologies possible for the first time. These technologies have the potential to open new fields of real-world neuroscience by enabling functional neuroimaging of the human cortex at a resolution comparable to fMRI in almost any environment and population. In this perspective article, we provide a brief overview of the history and the current status of wearable high-density fNIRS and DOT approaches, discuss the greatest ongoing challenges, and provide our thoughts on the future of this remarkable technology.
The ventromedial and dorsolateral prefrontal cortex are two major prefrontal regions that usually interact in serving different cognitive functions. On the other hand, these regions are also involved in cognitive processing of emotions but their contribution to emotional processing is not well-studied. In the present study, we investigated the role of these regions in three dimensions (valence, arousal and dominance) of emotional processing of stimuli via ratings of visual stimuli performed by the study participants on these dimensions. Twenty- two healthy adult participants (mean age 25.21 ± 3.84 years) were recruited and received anodal and sham transcranial direct current stimulation (tDCS) (1.5 mA, 15 min) over the dorsolateral prefrontal cortex (dlPFC) and and ventromedial prefrontal cortex (vmPFC) in three separate sessions with an at least 72-h interval. During stimulation, participants underwent an emotional task in each stimulation condition. The task included 100 visual stimuli and participants were asked to rate them with respect to valence, arousal, and dominance. Results show a significant effect of stimulation condition on different aspects of emotional processing. Specifically, anodal tDCS over the dlPFC significantly reduced valence attribution for positive pictures. In contrast, anodal tDCS over the vmPFC significantly reduced arousal ratings. Dominance ratings were not affected by the intervention. Our results suggest that the dlPFC is involved in control and regulation of valence of emotional experiences, while the vmPFC might be involved in the extinction of arousal caused by emotional stimuli. Our findings implicate dimension-specific processing of emotions by different prefrontal areas which has implications for disorders characterized by emotional disturbances such as anxiety or mood disorders.
Despite the strong evidence linking psychological stress to disease risk, health researchers often fail to include psychological stress in models of health. One reason for this is the incorrect perception that the construct of psychological stress is too vague and broad to accurately measure. This article describes best practices in stress measurement, detailing which dimensions of stressor exposures and stress responses to capture, and how. We describe when to use psychological versus physiological indicators of stress. It is crucial that researchers across disciplines utilize the latest methods for measuring and describing psychological stress in order to build a cumulative science.
In alcohol hangover research, both naturalistic designs and randomized controlled trials (RCTs) are successfully employed to study the causes, consequences, and treatments of hangovers. Although increasingly applied in both social sciences and medical research, the suitability of naturalistic study designs remains a topic of debate. In both types of study design, screening participants and conducting assessments on-site (e.g., psychometric tests, questionnaires, and biomarker assessments) are usually equally rigorous and follow the same standard operating procedures. However, they differ in the levels of monitoring and restrictions imposed on behaviors of participants before the assessments are conducted (e.g., drinking behaviors resulting in the next day hangover). These behaviors are highly controlled in RCTs and uncontrolled in naturalistic studies. As a result, the largest difference between naturalistic studies and RCTs is their ecological validity, which is usually significantly lower for RCTs and (related to that) the degree of standardization of experimental intervention, which is usually significantly higher for RCTs. In this paper, we specifically discuss the application of naturalistic study designs and RCTs in hangover research. It is debated whether it is necessary to control certain behaviors that precede the hangover state when the aim of a study is to examine the effects of the hangover state itself. If the preceding factors and behaviors are not in the focus of the research question, a naturalistic study design should be preferred whenever one aims to better mimic or understand real-life situations in experimental/intervention studies. Furthermore, to improve the level of control in naturalistic studies, mobile technology can be applied to provide more continuous and objective real-time data, without investigators interfering with participant behaviors or the lab environment impacting on the subjective state. However, for other studies, it may be essential that certain behaviors are strictly controlled. It is, for example, vital that both test days are comparable in terms of consumed alcohol and achieved hangover severity levels when comparing the efficacy and safety of a hangover treatment with a placebo treatment day. This is best accomplished with the help of a highly controlled RCT design.
Various internal and external factors negatively affect the homeostatic equilibrium of organisms at the molecular to the whole-body level, inducing the so-called state of stress. Stress affects an organism’s welfare status and induces energy-consuming mechanisms to combat the subsequent ill effects; thus, the individual may be immunocompromised, making them vulnerable to pathogens. The information presented here has been extensively reviewed, compiled, and analyzed from authenticated published resources available on Medline, PubMed, PubMed Central, Science Direct, and other scientific databases. Stress levels can be monitored by the quantitative and qualitative measurement of biomarkers. Potential markers of stress include thermal stress markers such as heat shock proteins (HSPs), innate immune markers such as Acute Phase Proteins (APPs), oxidative stress markers, and chemical secretions in the saliva and urine. In addition, stress biomarkers also play critical roles in the prognosis of stress-related diseases and disorders, and therapy guidance. Moreover, different components have been identified as potent mediators of cardiovascular, central nervous system, hepatic, and nephrological disorders, which can also be employed to evaluate these conditions precisely, but with stringent validation and specificity. Considerable scientific advances have been made in the detection, quantitation, and application of these biomarkers. The present review describes the current progress of identifying biomarkers, their prognostic, and therapeutic values.
Background:
It has become possible for the new generation of consumer wristbands to classify sleep stages based on multisensory data. Several studies have validated the accuracy of one of the latest models, that is, Fitbit Charge 2, in measuring polysomnographic parameters, including total sleep time, wake time, sleep efficiency (SE), and the ratio of each sleep stage. Nevertheless, its accuracy in measuring sleep stage transitions remains unknown.
Objective:
This study aimed to examine the accuracy of Fitbit Charge 2 in measuring transition probabilities among wake, light sleep, deep sleep, and rapid eye movement (REM) sleep under free-living conditions. The secondary goal was to investigate the effect of user-specific factors, including demographic information and sleep pattern on measurement accuracy.
Methods:
A Fitbit Charge 2 and a medical device were used concurrently to measure a whole night's sleep in participants' homes. Sleep stage transition probabilities were derived from sleep hypnograms. Measurement errors were obtained by comparing the data obtained by Fitbit with those obtained by the medical device. Paired 2-tailed t test and Bland-Altman plots were used to examine the agreement of Fitbit to the medical device. Wilcoxon signed-rank test was performed to investigate the effect of user-specific factors.
Results:
Sleep data were collected from 23 participants. Sleep stage transition probabilities measured by Fitbit Charge 2 significantly deviated from those measured by the medical device, except for the transition probability from deep sleep to wake, from light sleep to REM sleep, and the probability of staying in REM sleep. Bland-Altman plots demonstrated that systematic bias ranged from 0% to 60%. Fitbit had the tendency of overestimating the probability of staying in a sleep stage while underestimating the probability of transiting to another stage. SE>90% (P=.047) was associated with significant increase in measurement error. Pittsburgh sleep quality index (PSQI)<5 and wake after sleep onset (WASO)<30 min could be associated to significantly decreased or increased errors, depending on the outcome sleep metrics.
Conclusions:
Our analysis shows that Fitbit Charge 2 underestimated sleep stage transition dynamics compared with the medical device. Device accuracy may be significantly affected by perceived sleep quality (PSQI), WASO, and SE.
Consumersleep trackingtechnologies offer anunobtrusive and cost-efficient waytomonitor sleepinfree-livingconditions.Technologicaladvancesinhardwareand software have significantly improved the functionality of the new gadgets that recently appeared in the market. However, whether the latest gadgets can provide valid measurements on overall sleep parameters and sleep structure such as deep and REM sleep has not been examined. In this study, we aimed to investigate the validity of the latest consumer sleep tracking devices including an activity wristband Fitbit Charge 2 and a wearable EEG-based eye mask Neuroon in comparison to a medical sleep monitor. First, we confirmed that Fitbit Charge 2 can automatically detect the onset and offset of sleep with reasonable accuracy. Second, analysis found that both consumer devices produced comparable results in measuring total sleep duration and sleep efficiency compared to the medical device. In addition, Fitbit accurately measured the number of awakenings, while Neuroon with good signal quality had satisfactory performance on total awake time and sleep onset latency. However, measuring sleep structure including light, deep, and REM sleep remains to be challenging for both consumer devices. Third,greater discrepancies were observed between Neuroon and the medical device in nights with more disrupted sleep and when the signal quality was poor, but no trend was observed in Fitbit Charge 2. This study suggests that current consumer sleep tracking technologies may be immature for diagnosing sleep disorders, but they are reasonably satisfactory for general purpose and non-clinical use.
Stress can influence health throughout the lifespan, yet there is little agreement about what types and aspects of stress matter most for human health and disease. This is in part because "stress" is not a monolithic concept but rather, an emergent process that involves interactions between individual and environmental factors, historical and current events, allostatic states, and psychological and physiological reactivity. Many of these processes has alone been labeled as "stress." Stress science would be further advanced if researchers adopted a common conceptual model that incorporates epidemiological, affective, and psychophysiological perspectives, with more precise language for describing stress measures. We articulate an integrative working model, highlighting how stressor exposures across the life course influence habitual responding and stress reactivity, and how health behaviors interact with stress. We offer a Stress Typology articulating timescales for stress measurement - acute, event-based, daily, and chronic-- and more precise language for dimensions of stress measurement.
Adrenal glucocorticoids are major modulators of multiple functions, including energy metabolism, stress responses, immunity, and cognition. The endogenous secretion of glucocorticoids is normally characterized by a prominent and robust circadian (around 24 hours) oscillation, with a daily peak around the time of the habitual sleep-wake transition and minimal levels in the evening and early part of the night. It has been long recognized that this 24-h rhythm partly reflects the activity of a master circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus. In the past decade, secondary circadian clocks based on the same molecular machinery as the central master pacemaker were found in other brain areas as well as in most peripheral tissues, including the adrenal glands. Evidence is rapidly accumulating to indicate that misalignment between central and peripheral clocks has a host of adverse effects. The robust rhythm in circulating glucocorticoid levels has been recognized as a major internal synchronizer of the circadian system. The present review examines the scientific foundation of these novel advances and their implications for health, and disease prevention and treatment.
Getting enough quality sleep is a key part of a healthy lifestyle. Many people are tracking their sleep through mobile and wearable technology, together with contextual information that may influence sleep quality, like exercise, diet, and stress. However, there is limited support to help people make sense of this wealth of data, i.e., to explore the relationship between sleep data and contextual data. We strive to bridge this gap between sleep-tracking and sense-making through the design of SleepExplorer, a web-based tool that helps individuals understand sleep quality through multi-dimensional sleep structure and explore correlations between sleep data and contextual information. Based on a two-week field study with 12 participants, this paper offers a rich understanding on how technology can support sense-making on personal sleep data: SleepExplorer organizes a flux of sleep data into sleep structure, guides sleep-tracking activities, highlights connections between sleep and contributing factors, and supports individuals in taking actions. We discuss challenges and opportunities to inform the work of researchers and designers creating data-driven health and well-being applications.
In this article, we argued that the term stress has served as a valuable heuristic, helping researchers to integrate traditions that illuminate different stages of the process linking stressful life events to disease. We provided a short history of three traditions in the study of stress: the epidemiological, psychological, and biological. The epidemiological tradition focuses on defining which circumstances and experiences are deemed stressful on the basis of consensual agreement that they constitute threats to social or physical well-being. The psychological tradition focuses on individuals’ perceptions of the stress presented by life events on the basis of their appraisals of the threats posed and the availability of effective coping resources. The biological tradition focuses on brain-based perturbations of physiological systems that are otherwise essential for normal homeostatic regulation and metabolic control. The foci of these three traditions have informed elements of a stage model of disease, wherein events appraised as stressful are viewed as triggering affective states that in turn engender behavioral and biological responses having possible downstream implications for disease.
A Point of Care (POC) test for measurement of antibody or cortisol concentrations has given rapid feedback to coaches and support staff in Premier League soccer clubs within a matter of minutes from sample collection. This has been useful in assessing fatigue levels, immune status and readiness to train / compete and offers a considerable time advantage over standard laboratory methods. This current paper assesses a new POC reader, which is smaller, quicker and cheaper than the current model.
A total of 48 saliva samples taken during routine monitoring a cohort of English Premier League soccer players (23.5 ± 6.4 yrs) using IPRO OFC kits on two separate occasions for the measurement of cortisol on the standard IPRO ESE-Quant LFD reader and the new IPRO Cube reader. The next week 50 samples from the same cohort were measured for sIgA concentration with the IPRO Cube reader and the same samples analysed the next day via ELISA.
The cortisol LFD showed good agreement on both readers; r = 0.96 (95% CI 0.93 – 0.98) with typical error of estimate 1.18 nM (95% CI 0.98 – 1.48) and no difference between the mean values on each reader: ESE-Quant 7.5 nM (range 2.73 – 23.5 nM) v Cube 7.1 nM (range 2.24 – 25.8).
The sIgA LFD measured with the Cube reader showed good agreement with ELISA r = 0.97 (95% CI 0.95 – 0.98) with typical error of estimate 33.24 μg/mL and no difference between the mean values on the Cube and ELISA: Cube mean 215.6 ± 163.8 μg/mL (range 34.7 – 621.1 μg/mL) v ELISA mean 205.4 ± 142.1 (range 34.91 600 μg/mL.
The new Cube POC device shows suitable validity for use in the sporting environment and represents savings in cost and analysis time in comparison to previous methods.
Recent neuroimaging studies aimed at investigating effects of psychological stress on the neural activity have used a range of experimental paradigms to elicit an acute stress response. The goal of this review is to, first, summarize results from these studies from a perspective of task design and, second, assess the appropriateness of the different stress tasks used.
We completed a PubMed search on recent articles that have examined the effects of psychological stress on neural processes in a neuroimaging environment. Selected articles were arranged according to the stress task used in the following categories: script-driven stress stimuli, Stroop colour-word interference task, speech in front of an audience, serial subtraction, and Montreal Imaging Stress Task (MIST).
Only studies using serial subtraction or the MIST were able to induce a significant cortisol stress response in their participants. Most consistent findings include decreased activity in orbitofrontal regions in response to stress. Additional findings of note are increases in activity in the frontal lobes, particularly the anterior cingulate cortex, as well as deactivation of the limbic system, particularly the hippocampus.
Research to date is beginning to outline the involvement of prefrontal and limbic regions in perception and modulation of psychological stress. However, additional research is needed in designing a neuroimaging stress task that will yield a significant cortisol stress response consistently, across populations and laboratories.
Objective: The use of wearable motion-sensing technology offers important advantages over conventional methods for obtaining measures of physical activity and/or physical functioning in aged individuals. This review aims to identify the actual state of applying wearable systems for monitoring mobility-related activity in older populations. In this review we focus on technologies and applications, research designs, feasibility and adherence aspects, and clinical relevance of wearable motion-sensing technology.
Data sources: PubMed (MEDLINE since 1990), Ovid (BIOSIS, CINAHL), and Cochrane (Central) and reference lists of all relevant articles were searched.
Review methods: Two authors independently reviewed randomized and non-randomized trials on people above 65 years systematically. Quality of selected articles was scored and study results were summarised and discussed.
Results: Two hundred and twenty-seven abstracts were considered. After application of inclusion criteria and full text reading, 42 articles were taken into account in a full text review. Twenty of these papers evaluated walking with step counters, other papers used varying accelerometry approaches for obtaining overall activity measures (n = 16), or for monitoring changes in body postures and activity patterns (n = 17). Seven studies explicitly mentioned feasibility and/or adherence aspects. Eight studies presented outcome evaluations of interventions. Eight articles were representing descriptive research designs, three articles were using mixed descriptive and exploratory research designs, 23 articles used exploratory research-type designs, and eight articles used experimental research designs.
Conclusion: Although feasible methods for monitoring human mobility are available, evidence-based clinical applications of these methods in older populations are in need of further development.
The durations of successive sleep cycles, defined according to NREM (stage 2) or REM onsets, were objected to trend analysis in three groups of normal subjects and in a group of elderly patients with chronic brain syndrome (CBS). NREM sleep cycles showed consistent curvilinear trends for all groups except that the trend in children was distinguished by a lengthy first NREM cycle. REM steep cycles showed quite similar curvilinear trends for the three normal age groups with the middle two cycles being longer than the first and fourth. In the CBS patients, REM sleep cycles did not show a significant trend across the night. Real-time cycles (i.e., with time awake included) manifested trends quite similar to those excluding waking. The trends in sleep cycle durations are normative characteristics of sleep which may not be apparent on a single night. A more constant cycle was found in the CBS elderly and may indicate brain pathology. Sleep cycle trends, along with such other temporal characteristics as the decline in stage 4, may provide clues to the metabolic processes which underlie the sleep EEG. They also provide a more exact basis for investigation of hypothesized biorhythm correlates of NREM-REM cycles.
Quantitation of near infrared spectroscopic data in a scattering medium such as tissue requires knowledge of the optical pathlength in the medium. This can now be estimated directly from the time of flight of picosecond length light pulses. Monte Carlo modelling of light pulses in tissue has shown that the mean value of the time dispersed light pulse correlates with the pathlength used in quantitative spectroscopic calculations. This result has been verified in a phantom material. Time of flight measurements of pathlength across the rat head give a pathlength of 5.3 +/- 0.3 times the head diameter.
This paper describes a protocol for induction of moderate psychological stress in a laboratory setting and evaluates its effects on physiological responses. The 'Trier Social Stress Test' (TSST) mainly consists of an anticipation period (10 min) and a test period (10 min) in which the subjects have to deliver a free speech and perform mental arithmetic in front of an audience. In six independent studies this protocol has been found to induce considerable changes in the concentration of ACTH, cortisol (serum and saliva), GH, prolactin as well as significant increases in heart rate. As for salivary cortisol levels, the TSST reliably led to 2- to 4-fold elevations above baseline with similar peak cortisol concentrations. Studies are summarized in which TSST-induced cortisol increases elucidated some of the multiple variables contributing to the interindividual variation in adrenocortical stress responses. The results suggest that gender, genetics and nicotine consumption can influence the individual's stress responsiveness to psychological stress while personality traits showed no correlation with cortisol responses to TSST stimulation. From these data we conclude that the TSST can serve as a tool for psychobiological research.
Many university students experience stress that lead to negative effect on health and academic performance. In this paper we present the development of a mobile health application named NokoriMe, which consists of the design of an original academic stress questionnaire and the implementation of the application. NokoriMe application enables students to measure and track stress over time and to visualize trends and correlations in stress and physiological responses to stress (i.e. sleep quality and physical activity patterns). A pilot usability study shows that the developed application is intuitive to use, but there is room for further improvement on questionnaire design and data visualization.
Rumination is an involuntary cognitive process theorized to prolong arousal and inhibit proper emotion regulation. Most available research has examined individual differences in cognitive dispositions to ruminate about stress as a risk marker for psychopathology and other health problems. This intensive longitudinal study extended previous research by examining day-to-day associations of rumination about stress with objectively-measured actigraph-based sleep and diurnal salivary cortisol activity. Sixty-one healthy participants (Mage = 20.91) completed up to five ecological momentary assessments (EMA) each day and wore actigraph wristwatches for eight days (N = 488). On three of these days, participants provided five saliva samples assayed for cortisol (N = 910). On average, greater daily stress levels were associated with shorter sleep duration and higher waking cortisol levels. In day-to-day analyses, greater daily stress levels, when combined with ruminating about daily stress more than usual, was associated with higher waking cortisol levels the following morning. Ruminating more than usual about daily stress, in the context of low-stress days, was also associated with flatter diurnal cortisol slopes the next day. These findings highlight the potential influences of daily stress, and rumination about stress, on sleep and diurnal cortisol activity – two important markers of health and well-being.
Previous research indicates that sleep difficulties and stress are prevalent in college students. The main aim of the current study was to investigate the role of repetitive negative thinking (RNT), cognitive emotion regulation, and negative affect as mediators of the relationship between stress and sleep difficulties. We also intended to analyse the associations between all these variables and the gender differences. A sample of 549 college students completed self-report measures assessing the mentioned variables. Descriptive and correlational analyses showed significant differences between genders. In total sample, sleep difficulties were positively associated with perceived stress, negative affect, RNT and cognitive emotional strategies (rumination, self-blaming, catastrophizing, and acceptance). Mediation analyses suggested that in addition to the direct effect of stress on sleep difficulties, rumination and negative affect were mediators in this relationship (after controlling gender). RNT did not mediate this association; however it was significantly associated to rumination and/or negative affect. These findings suggest that the effect of stress on sleep difficulties is strengthened by rumination and/or negative affect. The negative impact of RNT (content free) only occurs if associated to rumination and/or negative affect.
A Point of Care (POC) test for measurement of salivary antibody or cortisol concentrations, using a Lateral Flow Device (LFD), has given rapid feedback to coaches and support staff in Premier League soccer clubs within a matter of minutes from sample collection. This has been useful in assessing fatigue levels, immune status and readiness to train/compete and offers a considerable time advantage over standard laboratory methods. This current paper assesses a new POC reader, which is smaller, quicker and cheaper than the current model. A total of 48 saliva samples taken during routine monitoring of a cohort of English Premier League soccer players (23.5 ± 6.4 y) using IPRO OFC kits on two separate occasions for the measurement of cortisol on the standard IPRO LFD Reader and the new IPRO Cube reader. The following week 50 samples from the same cohort were measured for sIgA concentration with both IPRO readers. The cortisol LFD showed good agreement on both readers; r = 0.96 (95% CI 0.93–0.98) with typical error of estimate 1.18 nM (95% CI 0.98–1.48) and no difference between the mean values on each reader: LFD Reader 7.5 nM (range 2.73–23.5 nM) v Cube 7.1 nM (range 2.24–25.8). The sIgA LFD measured with the Cube reader showed good agreement with the standard LFD Reader; r = 0.98 (95% CI 0.96–0.99) with typical error of estimate 29.9 (95% CI 24.9–37.4) μg/mL and higher but not significant different mean values on the Cube: mean 215.6 ± 163.8 μg/mL (range 34.7–621.1 μg/mL) v LFD Reader mean 148.3 ± 142.1 (range 20.0–518.8 μg/mL). The new Cube POC device shows suitable validity for use in the sporting environment and represents savings in cost and analysis time in comparison to previous methods.
Functional near-infrared spectroscopy (fNIRS) is a non-invasive method to measure brain activities using the changes of optical absorption in the brain through the intact skull. fNIRS has many advantages over other neuroimaging modalities such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), or magnetoencephalography (MEG), since it can directly measure blood oxygenation level changes related to neural activation with high temporal resolution. However, fNIRS signals are highly corrupted by measurement noises and physiology-based systemic interference. Careful statistical analyses are therefore required to extract neuronal activity-related signals from fNIRS data. In this paper, we provide an extensive reviewof historical developments of statistical analysis for fNIRS signal, which includes motion artifact correction, short source-detector separation correction, principal component analysis (PCA)/independent component analysis (ICA), false discovery rate (FDR), serially-correlated errors, as well as inference techniques such as the standard t-test, F-test, analysis of variance (ANOVA), and statistical parameter mapping (SPM) framework. In addition, to provide a unified view of various existing inference techniques, we explain a linear mixed effect model with restricted maximum likelihood (ReML) variance estimation, and show that most of the existing inference methods for fNIRS analysis can be derived as special cases. Some of the open issues in statistical analysis are also described.
Ambulatory assessments of hypothalamus–pituitary–adrenal axis responses to acute natural stressors yield evidence on stress regulation with high ecological validity. Sampling of salivary cortisol is a standard technique in this field.
In 21 healthy student teachers, we assessed cortisol responses to a demonstration lesson. On a control day, sampling was repeated at analogous times. Additionally, the cortisol awakening response (CAR) was assessed on both days. Participants were also exposed to a laboratory stressor, the Trier Social Stress Test, and rated their individual levels of chronic work stress.
In pre-to-post-stress assessment, cortisol levels declined after the lesson. However, post-stress cortisol levels were significantly higher compared with those on the control day. Also, the Trier Social Stress Test yielded higher cortisol responses when using the control day as reference baseline. Associations between the CAR and chronic stress measures were observed solely on the control day. There were no significant associations between cortisol responses to the natural and laboratory stressors.
Our results indicate that a control day might be an important complement in laboratory but especially in ambulatory stress research. Furthermore, associations between chronic stress measures and the CAR might be obscured by acute stress exposure. Finally, responses to the laboratory stressor do not seem to mirror natural stress responses. Copyright
The present study investigates the relationship between stress and health in young adults. We predicted that academic stressor exposure would lead to an increase in self-reported stress and health symptoms, as well as alterations in salivary secretory immunoglobulin A (SIgA) and salivary cortisol concentration. Thirty-four healthy participants were administered stress and health inventories and tested to assess SIgA and cortisol levels during a baseline (low-stress) session and during an examination (high-stress) session. Self-report stress and health scores increased between low- and high-stress sessions in all participants. Cortisol level also increased between study sessions, but only in those participants who experienced an increase in perceived stress. No changes in SIgA were observed. Multiple linear regression revealed that baseline SIgA and cortisol level moderated the relationship between stressor exposure and health outcome. Participants with low basal SIgA levels and high basal cortisol levels had poorer health outcomes during the examination session than did participants with high basal SIgA levels and low basal cortisol levels. Neither cortisol reactivity, nor SIgA reactivity moderated the relationship between stressor exposure and health outcome. These findings suggest that individual differences in basal immune and endocrine activity predict stress-related susceptibility to ill health. Copyright © 2006 John Wiley & Sons, Ltd.
Neurovascular coupling is the generic term for changes in cerebral metabolic rate of oxygen (CMRO(2)), cerebral blood flow, and cerebral blood volume related to brain activity. The goal of this paper is to better understand the effects of neurovascular coupling in the visual and motor cortices using frequency-domain near-infrared spectroscopy. Maps of concentration changes in oxyhemoglobin [O(2)Hb], deoxyhemoglobin [HHb], and total hemoglobin of the visual and motor cortices were generated during stimulation using a reversing checkerboard screen and palm-squeezing, respectively. Seven healthy volunteers of 18-37 years of age were included. In the visual cortex the patterns of [O(2)Hb] and [HHb] were strongly linearly correlated (r(2) > 0.8 in 13 of a total of 24 locations). In 20 locations the change in [O(2)Hb] was larger than 0.25 microM. The mean slope of the linear regression between [O(2)Hb] and [HHb] was -3.93 +/- 0.31 (SE). The patterns of the [O(2)Hb] and [HHb] traces over the motor cortex looked different. The [O(2)Hb] reached its maximum change a few seconds before the [HHb] reached its minimum. This was confirmed by the linear regression analysis (r(2) > 0.8 in none of 40 locations). In 20 locations the change in [O(2)Hb] was larger than 0.25 microM. The mean slope of the regression line was -1.76 +/- 0.20, which is significantly higher than that in the motor cortex (P < 0.0000001). Patterns of [O(2)Hb] and [HHb] differ among cortex areas. This implies that the regulation of perfusion in the visual cortex is different from that in the motor cortex. There is evidence that the CMRO(2) increases substantially in the visual cortex, while this is not the case for the motor cortex.
Neuroimaging methods can be used to investigate whether sleep disorders are associated with specific changes in brain structure or regional activity. However, it is still unclear how these new data might improve our understanding of the pathophysiology underlying adult sleep disorders. Here we review functional brain imaging findings in major intrinsic sleep disorders (i.e., idiopathic insomnia, narcolepsy, and obstructive sleep apnea) and in abnormal motor behavior during sleep (i.e., periodic limb movement disorder and REM sleep behavior disorder). The studies reviewed include neuroanatomical assessments (voxel-based morphometry, magnetic resonance spectroscopy), metabolic/functional investigations (positron emission tomography, single photon emission computed tomography, functional magnetic resonance imaging), and ligand marker measurements.
Based on the current state of the research, we suggest that brain imaging is a useful approach to assess the structural and functional correlates of sleep impairments as well as better understand the cerebral consequences of various therapeutic approaches. Modern neuroimaging techniques therefore provide a valuable tool to gain insight into possible pathophysiological mechanisms of sleep disorders in adult humans.
Estimation of optical pathlength through tissue from direct time of flight measurement
- D T Delpy
- M Cope
- P Van Der Zee
- S Arridge
- S Wray
- J Wyatt
D. T. Delpy, M. Cope, P. Van der Zee, S. Arridge, S. Wray, and J.
Wyatt, "Estimation of optical pathlength through tissue from direct
time of flight measurement," Phys. Med. Biol., vol. 33, pp. 1433-1442,
1988.