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Alpha EEG coherence in different brain states: An electrophysiological index of the arousal level in human subjects

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Abstract

The functional relationships between the brain areas supposedly involved in the generation of the alpha activity were quantified by means of INTRA- and INTER-hemispheric coherences during different arousal states (relaxed wakefulness, drowsiness at sleep onset, and rapid eye movement sleep) where such an activity can be clearly detectable in the human EEG. A significant decrease in the fronto-occipital as well as in the inter-frontal coherence values in the alpha range was observed with the falling of the vigilance level, which suggests that the brain mechanisms underlying these coherences are state dependent. Making fronto-frontal coherence values in the alpha frequency band useful indexes to discern between brain functional states characterized by a different arousal level.

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... Spontaneous alpha activity appears during wakefulness mainly with eyes closed and under conditions of relaxation and mental inactivity (Alvarez, Pascual-Marqui, & Valdes-Sosa, 1990;Brazier, 1968;Cantero et al., 1999a;Inouye, Shinosaki, Yagasaki, & Shimizu, 1986;Rodin & Rodin, 1995). However, there is evidence that increases in alpha band activity during sleep may be considered an indicator of arousal and cortical activation (American Sleep Disorders Association, 1992;Cantero, Atienza, Salas, & Gómez, 1999b;Figueredo-Rodríguez et al., 2009;Hasan & Broughton, 1994;Pivik & Harman, 1995;Tyson, Ogilvie, & Hunt, 1984). ...
... show high values during wakefulness that decrease during N-REMS and fall to minimum values during REMS (Cantero et al., 1999a(Cantero et al., , 1999b(Cantero et al., , 1999cCantero, Atienza, & Salas, 2000). Both spectral power and the h characteristics of alpha activity have been determined for humans, a primate species that sleeps in a horizontal posture and presents muscular atonia during REMS. ...
... This is the first study to characterize the prevalence and coherence of the theta, alpha, and beta rhythms in different cortical areas during wakefulness and sleep in spider monkeys. Considering that alpha activity during sleep is an indicator of arousal and cortical activation (American Sleep Disorders Association, 1992;Cantero et al., 1999b;Hasan & Broughton, 1994;Pivik & Harman, 1995;Tyson et al., 1984), that muscle atonia is not observed in spider monkeys during REMS, and that these primates sleep in a vertical position (Cruz-Aguilar et al., 2015, we hypothesized higher RP and EEG coherence of the alpha band during REMS compared with N-REMS. Likewise, we predicted that these features of EEG alpha activity would be accompanied by the vertical posture and lack of muscular atonia during REMS. ...
Article
There is evidence that some animal species have developed physiological and behavioral mechanisms to monitor potential predatory threats during rapid eye movement sleep (REMS). Nevertheless, it has not been reported in arboreal primates. The present study analyzed the sleeping postures, as well as the electromyographic and electroencephalographic (EEG) activities during three conditions: REMS, non-REMS (N-REMS), and wakefulness in spider monkeys. The study included six monkeys, whose EEGs were recorded at the O1-O2, C3, C4, F3, and F4 derivations to analyze relative power (RP) and interhemispheric, intrahemispheric, frontoposterior, and central-posterior coherence of frequency bands, which has been considered an index of arousal states. The bands analyzed were theta (4.0-7.0 Hz), alpha1 (8.0-10.5 Hz), alpha2 (11.0-13.5 Hz), and beta (14.0-30.0 Hz). Spider monkeys adopt a vertical posture during sleep, and in REMS a lack of muscular atonia was observed. The RP of the alpha bands at O1-O2 was higher during REMS than that during wakefulness, N-REMS1, and N-REMS2. At the C3 derivation, the RP of alpha1 was higher during REMS than that during N-REMS2. The RP of both alpha bands at the F4 derivation was higher during REMS than that during wakefulness, whereas REMS was characterized by a higher coherence between the F3 and O1-O2 derivations of the alpha2 band. These prevalences and the higher coherence of alpha bands during REMS could represent a correlate of behavioral traits and activated cortical areas related to a possible arousal state in spider monkeys while sleeping.
... Results have shown that prolonged wakefulness induces significant reductions of the efficient communication between brain regions, resulting in a loss of vigilance. Standard lineal methods such as cross-correlation and spectral coherence have revealed reduced EEG connectivity in theta, beta, and mainly in the alpha band after SD [24,25]. Likewise, techniques taking into account linear and nonlinear relationships, such as mutual information function and synchronization likelihood, have demonstrated that sustained wakefulness tends to attenuate EEG dependencies [19,26]. ...
... Also, the ratio of alpha to delta and theta has been considered a possible indicator of the alertness of the subjects [43]. Hence, delta, theta and alpha powers were calculated, as well as the magnitude squared coherence (MSC) in the alpha band, deemed as an electrophysiological index of the arousal level in humans [24,25]. Spectral estimation was performed using the Welch periodogram with 5-s Hanning windows and 25% of overlapping. ...
... In this sense, the results obtained in this study using spectral variables and coherence are in agreement with all previously published works. Despite the slight differences in defining the frequency boundaries of the spectral bands with respect to the literature [9][10][11][12]44,56], known findings during sleep deprivation were reproduced: increases in theta activity and decreases in alpha power and coherence [7][8][9]12,24]. ...
Article
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Sleep deprivation (SD) has adverse effects on mental and physical health, affecting the cognitive abilities and emotional states. Specifically, cognitive functions and alertness are known to decrease after SD. The aim of this work was to identify the directional information transfer after SD on scalp EEG signals using transfer entropy (TE). Using a robust methodology based on EEG recordings of 18 volunteers deprived from sleep for 36 h, TE and spectral analysis were performed to characterize EEG data acquired every 2 h. Correlation between connectivity measures and subjective somnolence was assessed. In general, TE showed medium- and long-range significant decreases originated at the occipital areas and directed towards different regions, which could be interpreted as the transfer of predictive information from parieto-occipital activity to the rest of the head. Simultaneously, short-range increases were obtained for the frontal areas, following a consistent and robust time course with significant maps after 20 h of sleep deprivation. Changes during sleep deprivation in brain network were measured effectively by TE, which showed increased local connectivity and diminished global integration. TE is an objective measure that could be used as a potential measure of sleep pressure and somnolence with the additional property of directed relationships.
... Coherence measures showed that interregional alpha oscillation synchrony substantially diminishes between frontal and occipital regions and between contralateral homologues in frontal and temporal areas (Cantero, Atienza, Salas, & Gómez, 1999;Wright et al., 1995), with the decline starting before the SO, when slow eye movements appear and alpha activity is still observable in the EEG (Cantero et al., 1999). The coherence in lower alpha (8-11 Hz) band across the majority of brain regions continues to fall during the transition to stage 1, reaching its minimum at the NREM plateau, before the onset of sleep stage 2 (Morikawa et al., 2002). ...
... Coherence measures showed that interregional alpha oscillation synchrony substantially diminishes between frontal and occipital regions and between contralateral homologues in frontal and temporal areas (Cantero, Atienza, Salas, & Gómez, 1999;Wright et al., 1995), with the decline starting before the SO, when slow eye movements appear and alpha activity is still observable in the EEG (Cantero et al., 1999). The coherence in lower alpha (8-11 Hz) band across the majority of brain regions continues to fall during the transition to stage 1, reaching its minimum at the NREM plateau, before the onset of sleep stage 2 (Morikawa et al., 2002). ...
... A previous study of alpha coherence demonstrated that functional interaction between posterior and anterior brain regions might be involved in generating alpha rhythm during the waking time (Wang et al., 1992). Alpha coherence can be applied to illustrate the functional relationship between different brain regions (Achermann and Borbely, 1998;Cantero et al., 1999;Jorge et al., 2017). The fronto-occipital fasciculi physiologically supports this long-range interaction (Mai et al., 2004). ...
... The fronto-occipital fasciculi physiologically supports this long-range interaction (Mai et al., 2004). Alpha coherence can discern different arousal levels and is a sensitive index to evaluate various mental states (Cantero et al., 1999). For example, alpha coherence is reduced in patients with Alzheimer's disease during Examples of linear regressions for channel Fz of one participant. ...
Article
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Background Brain oscillations facilitate interaction within the brain network and between the brain and heart activities, and the alpha wave, as a prominent brain oscillation, plays a major role in these coherent activities. We hypothesize that mindfully breathing can make the brain and heart activities more coherent in terms of increased connectivity between the electroencephalogram (EEG) and electrocardiogram (ECG) signals. Methods Eleven participants (28–52 years) attended 8 weeks of Mindfulness Based Stress Reduction (MBSR) training. EEG and ECG data of two states of mindful breathing and rest, both eye-closed, were recorded before and after the training. EEGLAB was used to analyze the alpha band (8–12 Hz) power, alpha peak frequency (APF), peak power and coherence. FMRIB toolbox was used to extract the ECG data. Heart coherence (HC) and heartbeat evoked potential (HEP) were calculated for further correlation analysis. Results After 8 weeks of MBSR training, the correlation between APF and HC increased significantly in the middle frontal region and bilateral temporal regions. The correlation between alpha coherence and heart coherence had similar changes, while alpha peak power did not reflect such changes. In contrast, spectrum analysis alone did not show difference before and after MBSR training. Conclusion The brain works in rhythmic oscillation, and this rhythmic connection becomes more coherent with cardiac activity after 8 weeks of MBSR training. Individual APF is relatively stable and its interplay with cardiac activity may be a more sensitive index than power spectrum by monitoring the brain-heart connection. This preliminary study has important implications for the neuroscientific measurement of meditative practice.
... Coherence is a parameter that is widely used to study the functional brain network [15,[119][120][121][122][123][124] and is reliable for evaluating physiological abnormalities [125,126]. Coherence refers to the degree of association between two brain regions. ...
... Functional connectivity estimators were computed using the coherence method, which has been shown to be sufficient to capture the amount of shared activity between brain regions in the frequency domain [15,[119][120][121][122][123][124]. ...
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The perception of physical exertion is the cognitive sensation of work demands associated with voluntary muscular actions. Measurements of exerted force are crucial for avoiding the risk of overexertion and understanding human physical capability. For this purpose, various physiological measures have been used; however, the state-of-the-art in-force exertion evaluation lacks assessments of underlying neurophysiological signals. The current study applied a graph theoretical approach to investigate the topological changes in the functional brain network induced by predefined force exertion levels for twelve female participants during an isometric arm task and rated their perceived physical comfort levels. The functional connectivity under predefined force exertion levels was assessed using the coherence method for 84 anatomical brain regions of interest at the electroencephalogram (EEG) source level. Then, graph measures were calculated to quantify the network topology for two frequency bands. The results showed that high-level force exertions are associated with brain networks characterized by more significant clustering coefficients (6%), greater modularity (5%), higher global efficiency (9%), and less distance synchronization (25%) under alpha coherence. This study on the neurophysiological basis of physical exertions with various force levels suggests that brain regions communicate and cooperate higher when muscle force exertions increase to meet the demands of physically challenging tasks.
... Furthermore, studies of alpha synchrony in frontoparietal networks indicate that this EEG feature is an indicator of vigilance. Whereas some sleep studies have shown that in healthy individuals, alpha synchrony decreases with increasing sleep depth (decreasing vigilance) [41,42], studies on daytime cognitive performance have found that alpha synchrony increases in taskrelevant regions of the brain only while they perform the task [43][44][45][46][47]. Interestingly, the cognitive functions examined in the latter studies are impaired in PTSD and other psychiatric disorders, such as mild cognitive impairment [48] and depression [49]. Together, these findings suggest that the increased alpha synchrony we observed in PTSD subjects during NREM sleep is associated with disturbed sleep (due to hypervigilance) and may influence cognitive memory processes. ...
... Of these, three found such alterations during resting wakefulness. Lee et al. [10] computed synchrony between 62 EEG channels pairwise in the delta through gamma bands (32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50) for each subject in a non-PTSD group and a PTSD group that included subjects on medication. Then, for each group, they averaged the pairwise synchrony values across subjects and, setting the overall mean synchrony of the group plus one standard deviation as the threshold, obtained binary synchrony matrices for each frequency band. ...
Article
Study Objectives We assessed whether the synchrony between brain regions, analyzed using electroencephalography (EEG) signals recorded during sleep, is altered in subjects with post-traumatic stress disorder (PTSD) and whether the results are reproducible across consecutive nights and subpopulations of the study. Methods Seventy-eight combat-exposed veteran men with (n = 31) and without (n = 47) PTSD completed two consecutive laboratory nights of high-density EEG recordings. We computed a measure of synchrony for each EEG channel-pair across three sleep stages [rapid eye movement (REM) and non-REM stages 2 and 3] and six frequency bands. We examined the median synchrony in nine region-of-interest (ROI) pairs consisting of six bilateral brain regions (left and right frontal, central, and parietal regions) for ten frequency-band and sleep-stage combinations. To assess reproducibility, we used the first 47 consecutive subjects (18 with PTSD) for initial discovery and the remaining 31 subjects (13 with PTSD) for replication. Results In the discovery analysis, five alpha-band synchrony pairs during non-REM sleep were consistently larger in PTSD subjects compared to controls (effect sizes ranging from 0.52 to 1.44) across consecutive nights: two between the left-frontal and left-parietal ROIs, one between the left-central and left-parietal ROIs, and two across central and parietal bilateral ROIs. These trends were preserved in the replication set. Conclusion PTSD subjects showed increased alpha-band synchrony during non-REM sleep in the left fronto-parietal, left centro-parietal, and inter-parietal brain regions. Importantly, these trends were reproducible across consecutive nights and subpopulations. Thus, these alterations in alpha synchrony may be discriminatory of PTSD.
... Spindles (12)(13)(14)(15) are one of the most dominant EEG oscillations during NREM stage 2 sleep, and they have a lower density in deeper slow-wave sleep (SWS). Both the alpha power and the spindle power change in all parts of the cortex from wakefulness to different stages of sleep [35][36][37][38]. The origin of spindle waves shares a similar mechanism with alpha waves, as the GABAergic reticular nucleus in the thalamus is the pacemaker of this spindle rhythm, and the thalamocortical neurons and cortical neurons potentiate the genesis of spindle waves [39][40][41][42]. ...
... In our study, we confirmed the hierarchical changes in the propofol-induced reduction of occipital alpha oscillations during moderate sedation and propofol-induced alpha anteriorization during LOC. The topographic representation of alpha activity changes by dexmedetomidine is similar to that of sleep, with attenuation of alpha power across the frontal-posterior cortex [35][36][37]. The effect of dexmedetomidine on the HTCs has not been described. ...
Article
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Sedation induces changes in electroencephalography (EEG) dynamics. However, the distinct EEG dynamic characteristics at comparable sedation levels have not been well studied, resulting in potential interpretation errors in EEG monitoring during sedation. We aimed to analyze the EEG dynamics of dexmedetomidine and propofol at comparable sedation levels and to explore EEG changes with increased sedation levels for each agent. We measured the Bispectral Index (BIS) and 20-channel EEG under dexmedetomidine and propofol sedation from wakefulness, moderate sedation, and deep sedation to recovery in healthy volunteers (n = 10) in a randomized, 2-day, crossover study. Observer’s Assessment of Alertness and Sedation (OAA/S) score was used to assess sedation levels. Despite similar changes in increased delta oscillations, multiple differences in the EEG spatiotemporal dynamics were observed between these two agents. During moderate sedation, both dexmedetomidine and propofol induced increased spindle power; however, dexmedetomidine decreased the global alpha/beta/gamma power, whereas propofol decreased the alpha power in the occipital area and increased the global spindle/beta/gamma power. During deep sedation, dexmedetomidine was associated with increased fronto-central spindle power and decreased global alpha/beta/gamma power, but propofol was associated with increased theta/alpha/spindle/beta power, which was maximized in the frontal area. The transition of topographic alpha/spindle/beta power distribution from moderate sedation to deep sedation completely differed between these two agents. Our study demonstrated that there was a distinct hierarchy of EEG changes with increased sedation depths by propofol and dexmedetomidine. Differences in EEG dynamics at the same sedation level might account for differences in the BIS value and reflect the different sedation mechanisms. EEG-based clinical sedation monitoring should consider the effect of drug types on EEG dynamics.
... Those authors further reported decreases in alpha synchronization 2-3 min before SOP, and detected significant increases in the synchronization of the fast frequencies just before the installation of stage 2 of non-rapid eye movement sleep (N-REM2) [30]. Likewise, a significant decrease in fronto-occipital and inter-frontal synchronization in the alpha band has been observed during SOP [31]. Finally, Kikuchi et al. conducted a study to examine interhemispheric EEG synchronization during the state of rest in elderly subjects, finding low EEG synchronization for the delta, theta, alpha and beta bands [32]. ...
... Asterisks indicate significant differences with *p ≤ 0.05. synchronization during SOP in healthy subjects is associated with decreased correlation in the alpha band [28,[30][31][32]. ...
Article
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There is evidence demonstrating that 5-mg of fast-release melatonin significantly reduces nocturnal sleep onset in patients with mild-to-moderate Alzheimer’s disease (AD). However, the physiological mechanism that could promote sleep installation by melatonin in patients with AD is still poorly understood. The present pilot study was designed to analyze the effects of melatonin on cortical activity during the sleep onset period (SOP) in eight mild-to-moderate AD patients treated with 5-mg of fast-release melatonin. Electroencephalographic recordings were obtained from C3-A1, C4-A2, F7-T3, F8-T4, F3-F4, and O1-O2. The relative power (RP), interhemispheric, intrahemispheric, and fronto-posterior correlations of six electroencephalographic bands were calculated and compared between two conditions: placebo and melatonin. Results show that at F7-T3, F3-F4, and C3-A1, melatonin induced an increase of the RP of the delta band. Likewise, in F7-T3, melatonin induced a decrease of the RP in the alpha1 band. Similarly, results show a lower interhemispheric correlation between the F7-T3 and F8-T4 derivations in the alpha1 band compared to the placebo condition. We conclude that the short sleep onset related to melatonin intake in AD patients was associated with a lower RP of the alpha1, a higher RP of the delta band (mainly in the left hemisphere) and a decreased interhemispheric EEG coupling in the alpha1 band. The possible role of the GABAergic neurotransmission as well as of the cascade of neurochemical events that melatonin triggers on sleep onset are discussed.
... Large-scale synchronization of oscillatory activity is a crucial mechanism in the formation of functionally connected neuronal ensembles underlying a wide range of cognitive phenomena [33][34][35]. Accordingly, frequency-specific synchronous oscillations across distant electrode sites can characterize different states of vigilance [36,37] or cognitive processes that vary in difficulty, attentional demands, or multimodal integration [38][39][40]. In spite of the advantages of such analyses, apart from one recent study in epileptic patients [41], phasic and tonic REM states were not systematically analyzed in terms of EEG synchronization. ...
... In light of the aforementioned data, we assumed that tonic REM sleep was a more wake-like state with enhanced alertness and reinstated attentional processes anticipating environmental stimuli. We were specifically interested in long-range α synchronization that was shown to reflect increased arousal and alertness [25,36] and to play a key role in cognitive processes that require enhanced attention [38,39], multisensory integration [40,43], or top-down control [34,44]. Here, we show that long-range interand intrahemispheric α or β synchrony is enhanced in tonic periods in contrast to phasic ones. ...
Article
Rapid Eye Movement (REM) sleep is characterized by the alternation of two markedly different microstates, phasic and tonic REM. These periods differ in awakening and arousal thresholds, sensory processing, and spontaneous cortical oscillations. Previous studies indicate that whereas in phasic REM, cortical activity is independent of the external environment, attentional functions and sensory processing are partially maintained during tonic periods. Large-scale synchronization of oscillatory activity, especially in the alpha and beta frequency ranges can accurately distinguish different states of vigilance and cognitive processes of enhanced alertness and attention. Therefore, we examined long-range inter-and intrahemispheric, as well as short-range EEG synchronization during phasic and tonic REM periods quantified by the weighted phase lag index. Based on the nocturnal polysomnographic data of 19 healthy, adult participants we showed that long-range inter-and intrahemispheric alpha and beta synchrony were enhanced in tonic REM states in contrast to phasic ones, and resembled alpha and beta synchronization of resting wakefulness. On the other hand, short-range synchronization within the gamma frequency range was higher in phasic as compared to tonic periods. Increased short-range synchrony might reflect local, and inwardly driven sensorimotor activity during phasic REM periods, whereas enhanced long-range synchrony might index frontoparietal activity that reinstates environmental alertness after phasic REM periods.
... Based on EEG recordings, we estimated three classes of measures: (1) measures estimating spectral powerraw and normalized power spectra, median spectral frequency (MSF), spectral edge 90 (SEF90), and spectral edge 95 (SEF95), (2) measures estimating information content-spectral entropy, Kolmogorov-Chaitin complexity (K) and permutation entropy, and (3) measures estimating functional connectivity-symbolic mutualiInformation (SMI) and weighted symbolic mutual information (wSMI). Power spectrum density (PSD) was computed over the delta (1-4 Hz), theta (4-8 Hz) alpha (8-12 Hz), beta (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), gamma (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) spectral bands, using the Welch spectrum approximation (segments = 512 ms, overlap = 400ms). Segment rejections were windowed using a Hanning window and zero-padded to 4096 samples. ...
Article
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Mind blanking (MB) is the inability to report mental events during unconstraint thinking. Previous work shows that MB is linked to decreased levels of cortical arousal, indicating dominance of cerebral mechanisms when reporting mental states. What remains inconclusive is whether MB can also ensue from autonomic arousal manipulations, pointing to the implication of peripheral physiology to mental events. Using experience sampling, neural, and physiological measurements in 26 participants, we first show that MB was reported more frequently in low arousal conditions, elicited by sleep deprivation. Also, there was partial evidence for a higher occurence of MB reports in high arousal conditions, elicited by intense physical exercise. Transition probabilities revealed that, after sleep deprivation, mind wandering was more likely to be followed by MB and less likely to be followed by more mind wandering reports. Using classification schemes, we found higher performance of a balanced random forest classifier trained on both neural and physiological markers in comparison to performance when solely neural or physiological were used. Collectively, we show that both cortical and autonomic arousal affect MB report occurrences. Our results establish that MB is supported by combined brain-body configurations, and, by linking mental and physiological states, they pave the way for novel embodied accounts of spontaneous thinking. ‘The stage 1 protocol for this Registered Report was accepted in principle on 02/01/23. The protocol, as accepted by the journal, can be found at: 10.17605/OSF.IO/SH2YE’ Techniques: Life sciences techniques, Biophysical methods [Electrocardiography - EKG]; Life sciences techniques, Biophysical methods [Electroencephalography - EEG]; CTS received date: 27.11.2024.
... Few studies have characterized changes in alpha coherence in local field potentials across areas with arousal state in primates. In humans, change in frontal-occipital alpha coherence was reported between eye closure and sleep (Cantero et al. 1999) Fig. 1. A) Comparison of high and low arousal power spectra across regions. ...
Article
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Arousal states are thought to influence many aspects of cognition and behavior by broadly modulating neural activity. Many studies have observed arousal-related modulations of alpha (~8 to 15 Hz) and gamma (~30 to 50 Hz) power and coherence in local field potentials across relatively small groups of brain regions. However, the global pattern of arousal-related oscillatory modulation in local field potentials is yet to be fully elucidated. We simultaneously recorded local field potentials in numerous cortical and subcortical regions in the primate brain and assessed oscillatory activity and inter-regional coherence associated with arousal state. In high arousal states, we found a uniquely strong and coherent gamma oscillation between the amygdala and basal forebrain. In low arousal rest-like states, a relative increase in coherence at alpha frequencies was present across sampled brain regions, with the notable exception of the medial temporal lobe. We consider how these patterns of activity may index arousal-related brain states that support the processing of incoming sensory stimuli during high arousal states and memory-related functions during rest.
... It could be argued that these results could be attributed to higher arousal resulting from the presentation of naturalistic stimuli. Indeed, higher arousal has been associated with lower alpha power (55). However, alpha asymmetries are a relative measure, comparing left-hemispheric to right-hemispheric EEG activity. ...
Article
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Emotion induction in psychological and neuroscientific research has been mostly done by presenting participants with picture or film material. However, it is debatable whether this passive approach to emotion induction results in an affective state comparable to real-life emotions, and if the neural correlates of emotion processing are ecologically valid. To investigate the appropriateness of pictures for the induction of emotions, we presented 56 participants in a within-subjects design with naturalistic disgusting and neutral stimuli as well as with pictures of said stimulus material while recording continuous EEG data. We calculated asymmetry indices (AIs) for alpha power as an index of emotion processing and emotion regulation at the F3/4, F5/6, F7/8, and O1/2 electrode pairs. Participants reported higher disgust ratings for disgusting naturalistic compared to disgusting pictorial stimuli. Investigating changes in the EEG signal in participants with a pronounced disgust response (n = 38), we found smaller AIs for naturalistic stimuli compared to pictures. Moreover, in this disgusted sub-sample, there were smaller AIs in response to naturalistic disgusting stimuli compared to pictorial disgusting and neutral stimuli at the O1/2 electrode pair indicating stronger activation of the right relative to the left hemisphere by naturalistic stimuli. As the right hemisphere has been shown to display dominance in processing negative and withdrawal-associated emotions, this might indicate that naturalistic stimuli are more appropriate for the induction of emotions than picture stimuli. To improve the validity of results from emotion induction, future research should incorporate stimulus material that is as naturalistic as possible.
... High-density EEG recordings demonstrate that propofol-induced frontal alpha waves are spatially coherent, possibly due to the anesthetics' effect on thalamocortical loops (Ching et al., 2010;Cimenser et al., 2011). Overall, the predominance of spatially coherent frontal alpha oscillations superimposed on delta and slow waves is a recurrently proposed spectral power distribution to recognize the unconscious state (Cantero et al., 1999;Gugino et al., 2001;Purdon et al., 2013). ...
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Background Induction of general anesthesia with propofol induces radical changes in cortical network organization, leading to unconsciousness. While perioperative frontal electroencephalography (EEG) has been widely implemented in the past decades, validated and age-independent EEG markers for the timepoint of loss of consciousness (LOC) are lacking. Especially the appearance of spatially coherent frontal alpha oscillations (8–12 Hz) marks the transition to unconsciousness. Here we explored whether decomposing the EEG spectrum into its periodic and aperiodic components unveiled markers of LOC and investigated their age-dependency. We further characterized the LOC-associated alpha oscillations by parametrizing the adjusted power over the aperiodic component, the center frequency, and the bandwidth of the peak in the alpha range. Methods In this prospective observational trial, EEG were recorded in a young (18–30 years) and an elderly age-cohort (≥ 70 years) over the transition to propofol-induced unconsciousness. An event marker was set in the EEG recordings at the timepoint of LOC, defined with the suppression of the lid closure reflex. Spectral analysis was conducted with the multitaper method. Aperiodic and periodic components were parametrized with the FOOOF toolbox. Aperiodic parametrization comprised the exponent and the offset. The periodic parametrization consisted in the characterization of the peak in the alpha range with its adjusted power, center frequency and bandwidth. Three time-segments were defined: preLOC (105 – 75 s before LOC), LOC (15 s before to 15 s after LOC), postLOC (190 – 220 s after LOC). Statistical significance was determined with a repeated-measures ANOVA. Results Loss of consciousness was associated with an increase in the aperiodic exponent (young: p = 0.004, elderly: p = 0.007) and offset (young: p = 0.020, elderly: p = 0.004) as well as an increase in the adjusted power (young: p < 0.001, elderly p = 0.011) and center frequency (young: p = 0.008, elderly: p < 0.001) of the periodic alpha peak. We saw age-related differences in the aperiodic exponent and offset after LOC as well as in the power and bandwidth of the periodic alpha peak during LOC. Conclusion Decomposing the EEG spectrum over induction of anesthesia into its periodic and aperiodic components unveiled novel age-independent EEG markers of propofol-induced LOC: the aperiodic exponent and offset as well as the center frequency and adjusted power of the power peak in the alpha range.
... Recent theories postulate that alpha-band oscillations act as a top-down inhibitory mechanism, implicated in attention selection 35 and that a decrease in alpha power is related to an increased attention and, more generally, to a stressful condition 29,36 . Hence, changes in alpha power can represent a useful psychophysical marker able to discern between brain functional states characterized by a different arousal level 37 . ...
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Successful aircraft cabin design depends on how the different stakeholders are involved since the first phases of product development. To predict passenger satisfaction prior to the manufacturing phase, human response was investigated in a Virtual Reality (VR) environment simulating a cabin aircraft. Subjective assessments of virtual designs have been collected via questionnaires, while the underlying neural mechanisms have been captured through electroencephalographic (EEG) data. In particular, we focused on the modulation of EEG alpha rhythm as a valuable marker of the brain’s internal state and investigated which changes in alpha power and connectivity can be related to a different visual comfort perception by comparing groups with higher and lower comfort rates. Results show that alpha-band power decreased in occipital regions during subjects’ immersion in the virtual cabin compared with the relaxation state, reflecting attention to the environment. Moreover, alpha-band power was modulated by comfort perception: lower comfort was associated with a lower alpha power compared to higher comfort. Further, alpha-band Granger connectivity shows top-down mechanisms in higher comfort participants, modulating attention and restoring partial relaxation. Present results contribute to understanding the role of alpha rhythm in visual comfort perception and demonstrate that VR and EEG represent promising tools to quantify human–environment interactions.
... High-density EEG recordings demonstrate that propofol-induced frontal alpha waves are spatially coherent, possibly due to the anesthetics' effect on thalamocortical loops (Ching et al., 2010;Cimenser et al., 2011). Overall, the predominance of spatially coherent frontal alpha oscillations superimposed on delta and slow waves is a recurrently proposed spectral power distribution to recognize the unconscious state (Cantero et al., 1999;Gugino et al., 2001;Purdon et al., 2013). ...
Article
Introduction: In the perioperative care, the effects of anesthesia on the brain are monitored with a frontal bispectral index monitor calculating an index between 0 (complete suppression of cortical activity) and 100 (fully awake) based on sinusoidal components of the EEG. Until today, anesthesiologists define loss of consciousness (LOC) clinically with the suppression of lid closure reflex or missing response. Routinely used monitors do not directly report the transition from awake to unconscious. An increase in frontal β power followed by predominant increased α power was proposed as a tool to track the transition between anesthetic states (Gugino, Chabot et al. 2001, Purdon, Pierce et al. 2013). Here we wanted to find common spectral signatures of LOC in young and elderly patients to implement in intraoperative neuromonitors. Methods: Patients without neurological diseases/medication aged >70 years and between 18 and 30 years undergoing elective orthopedic surgery were included. 20 Ag/AgCl electrodes were placed following the 10/20-system. Full-band EEG (DC-500Hz) was recorded intraoperatively with a sampling frequqency of 5000 Hz. Anesthesia was induced with propofol. EEGs were aligned at the event LOC. Power spectral analysis was computed with Chronux Toolbox in Matlab with the multitaper method for 6 frontal channels (Fp1, Fp2, F3, F4, F7, F8) and their mean was calculated. We used a custom-written Matlab code computing the 95% confidence interval of the median difference at each frequency between preLOC (1 min before LOC) and postLOC (1 min after LOC) to assess statistical significance for the difference in power by using a frequency domain-based bootstrapping algorithm resampling the Fourier coefficient. Results: 19 patients were included: 10 in the elderly cohort (80.6 +/- 3.2 years) and 9 in the young cohort (25.6 +/-2.9 years). In the young cohort, LOC was associated with a significant increase in δ, θ, α and β bands whereas the elderly cohort showed opposite dynamics with a decrease in sub-δ, δ and γ bands over LOC (Figure 1, 2). The power of fast components of the EEG (50-250 Hz) significantly dropped over LOC in both cohorts (Figure 2). Conclusion: Elderly patients undergoing anesthesia do not show the characteristic increased β and α power at LOC known from younger patients but rather a decrease in the slow components of the EEG (<8Hz). LOC is associated with a decrease in the fast components (>50Hz) in all patients. However commonly used neuromonitors do not measure faster components of the EEG. Further easily computable markers are needed to develop an EEG tool that reliably recognizes LOC in all patients. Legend Figure 1: Dynamics of Frontal Mean Power around LOC. Figure 2: Comparison of Power Distribution between preLOC & postLOC in the Young (left) and Elderly (right) Cohorts. A: Frontal Group Spectrogram over LOC B: Distribution of Frontal Spectral Power preLOC & postLOC C: 95% CI of median difference between preLOC & postLOC. • Download : Download high-res image (943KB) • Download : Download full-size image
... Neuroscience researchers have found that although the relationship between alpha power and different arousal levels could represent diverse brain functional states, boredom is an emotion related to alpha activity happening in both low-and high-arousal situations (Fahlman et al., 2013). Drowsiness, a low arousal emotion, weakens the alpha coherence of brain regions, which indicates an increase in internal attention and a decrease in vigilance level (Cantero et al., 1999). In contrast, high-arousal emotion strengthens the alpha coherence of brain regions and might imply external attention and distraction. ...
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Intelligent interaction alters previous human–machine task allocation patterns. Human workers will suffer from boredom and inattention, posing a significant challenge for the human–machine interaction loop. This study aims to investigate the relationship between boredom and prospective memory, which is a memory form including the detecting, identifying, and executing functions. Thus, the attention and memory mechanisms are critical to complete prospective memory tasks when bored. This study recruited twenty-eight participants and used electroencephalography to measure the alpha power in brain regions. The results indicated that parietal oscillations had a mediation effect on prospective memory, which could be associated with the frequent unstable attention. In addition, this study found that parietooccipital oscillations linked boredom and prospective memory, and the default mode network (DMN) and visual processing during boredom could better explain this finding. The findings of this study suggested that attention management and influences of processing visual information were starting points to cope with boredom because they could help prepare for prospective memory and make optimal decisions accordingly.
... The increase of alpha-1 coherence might be related to findings of Cantero et al. (1999) concerning significantly higher alpha coherence in frontal area compared to central and occipital locations during relaxation period. ...
... Xi et al. (Xi et al., 2018) demonstrated hierarchical changes in propofol-induced effects, including decreases in occipital α oscillations during moderate sedation and propofol-induced α anteriorization during loss of consciousness. Meanwhile, Dex has been shown to attenuate α oscillation power across the frontal-posterior cortex (Bhattacharya et al., 2014;Cantero et al., 2002;Cantero et al., 1999). Dex suppression of NE release from the LC reduces the hyperpolarization-activated current I h (Lee & McCormick, 1996) and leads to attenuated α oscillations. ...
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Background Although dexmedetomidine (Dex) is known to reduce bispectral index (BIS) values and propofol dosage, there is little information regarding raw electroencephalography (EEG) changes related to Dex deepening of propofol general anesthesia (GA). This study investigated the Dex effects on propofol GA via analysis of EEG changes. Methods A study cohort of 21 surgical patients (age range, 20–60 years) categorized as American Society of Anesthesiologists (ASA) class I or II was enrolled. We used time-varying spectral and bicoherence methods to compare electroencephalogram signatures 5 min before versus 10 min after intravenous Dex injection under propofol GA. The means and medians are reported with 95% confidence intervals (CIs) and inter-quartile ranges (IQRs), respectively. Results Dex augmented the slow waves power and theta ( θ ) oscillation bicoherence peak from a mean (95% CI) of 22.1% (19.0, 25.2) to 25.2% (21.8, 28.6). Meanwhile, Dex reduced alpha ( α ) peak power and bicoherence from 3.5 dB (1.0, 6.0) and 41.5% (34.0, 49.0) to 1.7 dB (− 0.6, 4.0) and 35.4% (29.0, 41.8), respectively, while diminishing the median frequency of α oscillation peak values and the mean frequency of α peaks in bicoherence spectra from 12.0 Hz (IQR 11.2, 12.6) and 11.7 Hz (11.3, 12.2) to 11.1 Hz (IQR 10.3, 11.8) and 11.2 Hz (10.9, 11.6), respectively. Conclusions Profound EEG changes support the supposition that Dex enhances propofol-induced GA from a moderate to a deeper state. The present findings provide a theoretical basis and reference regarding protocols aimed at reducing anesthetic/sedative dosage while maintaining sufficient depth of GA. Clinical trial registration ChiCTR, ChiCTR1900026955 . Registered on 27 October 2019
... It is worth pointing out that there is a noticeable increase in respiratory-locked alpha at the point of lowest TBR ( Figure 3C). As previous research has suggested that alpha frequencies are associated with cognitive inhibitory [95][96][97][98][99] and physiological arousal processes [100,101], this could signal some type of attentional braking or sudden increase inattentiveness and arousal during early to mid-inhalation, and this alpha oscillation could have relevance in the context of the oscillation of TBR. This requires further investigation, but given the well-documented relationship between arousal and attention [102] the idea seems plausible. ...
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Yogic and meditative traditions have long held that the fluctuations of the breath and the mind are intimately related. While respiratory modulation of cortical activity and attentional switching are established, the extent to which electrophysiological markers of attention exhibit synchronization with respiration is unknown. To this end, we examined (1) frontal midline theta-beta ratio (TBR), an indicator of attentional control state known to correlate with mind wandering episodes and functional connectivity of the executive control network; (2) pupil diameter (PD), a known proxy measure of locus coeruleus (LC) noradrenergic activity; and (3) respiration for evidence of phase synchronization and information transfer (multivariate Granger causality) during quiet restful breathing. Our results indicate that both TBR and PD are simultaneously synchronized with the breath, suggesting an underlying oscillation of an attentionally relevant electrophysiological index that is phase-locked to the respiratory cycle which could have the potential to bias the attentional system into switching states. We highlight the LC’s pivotal role as a coupling mechanism between respiration and TBR, and elaborate on its dual functions as both a chemosensitive respiratory nucleus and a pacemaker of the attentional system. We further suggest that an appreciation of the dynamics of this weakly coupled oscillatory system could help deepen our understanding of the traditional claim of a relationship between breathing and attention.
... It is worth pointing out that there is a noticeable increase in respiratory-locked alpha at the point of lowest TBR (figure 1). As previous research has suggested that alpha frequencies are associated with cognitive inhibitory (Klimesch, 2007;Mathewson, 2011;Pfurtscheller, 2003;Foxe and Snyder, 2011;Uusberg, 2013) and physiological arousal processes (Canteroa, 1999;Mikkuta, 2012), this could signal some type of attentional braking or sudden change in arousal during early to mid-inhalation, and this alpha oscillation could be relevant in the context of the oscillation of TBR. This requires further investigation, but given the well-documented relationship between arousal and attention (Eysenck, 2012) the idea seems plausible. ...
Preprint
Full-text available
Yogic and meditative traditions have long held that the fluctuations of the breath and the mind are intimately related. While respiratory modulation of cortical activity and attentional switching are established, the extent to which electrophysiological markers of attention exhibit synchronization with respiration is unknown. To this end, we examined 1) frontal midline theta-beta ratio, an indicator of attentional control state known to correlate with mind wandering episodes and functional connectivity of the executive control network; 2) pupil diameter (PD), a known proxy measure of locus coeruleus (LC) noradrenergic activity; and 3) respiration for evidence of phase synchronization and information transfer (multivariate Granger causality) during quiet restful breathing. Our results indicate that both TBR and PD are simultaneously synchronized with the breath, suggesting an underlying oscillation of an attentionally relevant electrophysiological index that is phase-locked to the respiratory cycle which could have the potential to bias the attentional system into switching states. We highlight the LC's pivotal role as a coupling mechanism between respiration and TBR, and elaborate on its dual functions as both a chemosensitive respiratory nucleus and a pacemaker of the attentional system. We further suggest that an appreciation of the dynamics of this weakly coupled oscillatory system could help deepen our understanding of the traditional claim of a relationship between breathing and attention.
... After age 7, the peak frequency of the dominant oscillation shifted to the faster alpha-band (8-12 Hz), and the peak alpha frequency continuously increased with age. Intrinsic, alpha-band neural oscillations have been shown to be modulated by alertness and attention (Cantero et al., 1999;Pfurtscheller et al., 1996;Romei et al., 2008). Prior EEG studies demonstrated that in toddlers, neural oscillations overlapping with the adult theta range of 4-8 Hertz in posterior electrodes can also be modulated by alertness, attention, and inhibitory control (Tatiana A Stroganova et al., 1999;Whedon et al., 2020). ...
Article
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Intrinsic, unconstrained neural activity exhibits rich spatial, temporal, and spectral organization that undergoes continuous refinement from childhood through adolescence. The goal of this study was to investigate the development of theta (4-8 Hertz) and alpha (8-12 Hertz) oscillations from early childhood to adulthood (years 3 to 24), as these oscillations play a fundamental role in cognitive function. We analyzed eyes-open, resting-state EEG data from 96 participants to estimate genuine oscillations separately from the aperiodic (1/f) signal. We examined age-related differences in the aperiodic signal (slope and offset), as well as the peak frequency and power of the dominant posterior oscillation. For the aperiodic signal, we found that both the aperiodic slope and offset decreased with age. For the dominant oscillation, we found that peak frequency, but not power, increased with age. Critically, early childhood (ages 3 to 7) was characterized by a dominance of theta oscillations in posterior electrodes, whereas peak frequency of the dominant oscillation in the alpha range increased between ages 7 and 24. Furthermore, theta oscillations displayed a topographical transition from dominance in posterior electrodes in early childhood to anterior electrodes in adulthood. Our results provide a quantitative description of the development of theta and alpha oscillations.
... Xi et al.14 demonstrated hierarchical changes in propofol-induced effects, including decreases in occipital α oscillations during moderate sedation and propofol-induced α anteriorization during loss of consciousness. Meanwhile, Dex has been shown to attenuate α oscillation power across the frontal-posterior cortex[23][24][25] . Dex suppression of NE release from the LC reduces the hyperpolarization-activated current Ih 26 and leads to attenuated α oscillations. ...
Preprint
Full-text available
Background: Although dexmedetomidine (Dex) is known to reduce bispectral index (BIS) values and propofol dosage, there is little information regarding raw electroencephalography (EEG) changes related to Dex deepening of propofol general anesthesia (GA). This study investigated Dex effects on propofol GA via analysis of EEG changes. Methods: A study cohort of 21 surgical patients (age range, 20–60 years) categorized asASA (American Society ofAnesthesiologists) class I or II were enrolled. We used time-varying spectral and bicoherence methods to compare electroencephalogram signatures 5 min before versus 10 min after intravenous Dex injection under propofol GA. Means and medians are reported with 95% confidence intervals (CIs) and inter-quartile ranges (IQRs), respectively. Results: Dex augmented the slow waves power and theta (θ) oscillation bicoherence peak from a mean (95% CI) of 22.1% (19.0, 25.2) to 25.2% (21.8, 28.6). Meanwhile, Dex reduced alpha (α) peak power and bicoherence from 3.5 dB (1.0, 6.0) and 41.5% (34.0, 49.0) to 1.7 dB (-0.6, 4.0) and 35.4% (29.0, 41.8), respectively, while diminishing the median frequency of α oscillation peak values and the mean frequency of α peaks in bicoherence spectra from 12.0 Hz (IQR: 11.2, 12.6) and 11.7 Hz (11.3, 12.2) to 11.1 Hz (IQR: 10.3, 11.8) Hz and 11.2 Hz (10.9, 11.6),respectively. Conclusions: Profound EEG changes support the supposition that Dex enhances propofol-induced GA from a moderate to a deeper state. The present findings provide a theoretical basis and reference regarding protocols aimed at reducing anesthetic/sedative dosage while maintaining sufficient depth of GA. Clinical trial registration: ChiCTR, ChiCTR1900026955, Registered 27 October 2019, http://www.chictr.org.cn/showproj.aspx?proj=44495
... However, there are also contradictions in the literature; for example, it has been reported that the functional connectivity of the alpha band in the parietal-to-frontal region [200] and of the alpha and beta bands in the frontal-to-parietal region [130] become weaker as mental fatigue increases. Furthermore, it has been shown that fronto-occipital coherence values in the alpha range decrease during the shift from alertness to drowsiness [207]. Results of the aforementioned studies support the notion that cortical-tocortical functional coupling-mainly in the frontal, central, Study reference ...
Article
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Graph theory analysis, a mathematical approach, has been applied in brain connectivity studies to explore the organization of network patterns. The computation of graph theory metrics enables the characterization of the stationary behavior of electroencephalogram (EEG) signals that cannot be explained by simple linear methods. The main purpose of this study was to systematically review the graph theory applications for mapping the functional connectivity of the EEG data in neuroergonomics. Moreover, this article proposes a pipeline for constructing an unweighted functional brain network from EEG data using both source and sensor methods. Out of 57 articles, our results show that graph theory metrics used to characterize EEG data have attracted increasing attention since 2006, with the highest frequency of publications in 2018. Most studies have focused on cognitive tasks in comparison with motor tasks. The mean phase coherence method, based on the “phase-locking value,” was the most frequently used functional estimation technique in the reviewed studies. Furthermore, the unweighted functional brain network has received substantially more attention in the literature than the weighted network. The global clustering coefficient and characteristic path length were the most prevalent metrics for differentiating between global integration and local segregation, and the small-worldness property emerged as a compelling metric for the characterization of information processing. This review provides insight into the use of graph theory metrics to model functional brain connectivity in the context of neuroergonomics research.
... 49 We also found a significant increase of alpha coherence between the central lobe and the right temporal lobe which showed the improvements of cognitive arousal level and brain functional. 50 Coherence provides a measure of the degree of synchronization between two signals, and we could assume there is a high degree of the coordinated brain activity between the underlying brain areas. ...
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Background Autism spectrum disorder (ASD) is a very complex neurodevelopmental disorder, characterized by social difficulties and stereotypical or repetitive behavior. Some previous studies using low‐frequency repetitive transcranial magnetic stimulation (rTMS) have proven of benefit in ASD children. Methods In this study, 32 children (26 males and six females) with low‐function autism were enrolled, 16 children (three females and 13 males; mean ± SD age: 7.8 ± 2.1 years) received rTMS treatment twice every week, while the remaining 16 children (three females and 13 males; mean ± SD age: 7.2 ± 1.6 years) served as waitlist group. This study investigated the effects of rTMS on brain activity and behavioral response in the autistic children. Results Peak alpha frequency (PAF) is an electroencephalographic measure of cognitive preparedness and might be a neural marker of cognitive function for the autism. Coherence is one way to assess the brain functional connectivity of ASD children, which has proven abnormal in previous studies. The results showed significant increases in the PAF at the frontal region, the left temporal region, the right temporal region and the occipital region and a significant increase of alpha coherence between the central region and the right temporal region. Autism Behavior Checklist (ABC) scores were also compared before and after receiving rTMS with positive effects shown on behavior. Conclusion These findings supported our hypothesis by demonstration of positive effects of combined rTMS neurotherapy in active treatment group as compared to the waitlist group, as the rTMS group showed significant improvements in behavioral and functional outcomes as compared to the waitlist group.
... Theta-(7-4 CPS) und Delta-Wellen (4 CPS >) entstehen im Schlaf, aber auch bei Aktivitäten, die eine hohe Konzentration erfordern, wie z.B. Meditieren, Zeichnen oder Schreiben (Bhattacharya & Petsche, 2005;Cantero, Atienza, Salas & Gómez, 1999). ...
Article
Einleitung: „Occupation as the center of practice” (Josman, 2010) ist der Kern der Ergotherapie. Die Evidenz für die Grundannahme, dass Betätigung heilende Wirkung hat, ist jedoch noch nicht ausreichend erforscht (Wilcock, 2007). Neuro-Occupation ist ein Konzept, in dem Betätigungen und neurologische Prozesse zusammengehörende und voneinander abhängige Einheiten sind (Padilla & Peyton, 1997). Dieser Review beschäftigt sich mit den Auswirkungen von Betätigung auf das menschliche Gehirn, die in der ergotherapeutischen Literatur beschrieben werden. Methode: Die Literaturrecherche wurde in den Datenbanken CINAHL® und PubMed® sowie in der Bibliothek der FH Campus Wien vom 28.02.2012 bis zum 21.03.2012 durchgeführt. Insgesamt wurden 40 Fachartikel und 5 Monographien bzw. Her-ausgeberbände berücksichtigt. Ergebnisse: Die Ergebnisse der Literaturrecherche thematisieren Auswirkungen von Musik und Zeichnen auf das mesocorticolimbische System, den Zusammenhang dieses Systems mit Veränderungen des Dopamin-Levels sowie die unterschiedliche Aktivierung der beiden Hemisphären durch bestimmte Betätigungen, wie beispielsweise Musik hören, Achtsamkeitstraining oder Zeichnen. Schlussfolgerung: Die Ergebnisse zeigen vielversprechende Auswirkungen von bestimmten Betäti-gungen auf das menschliche Gehirn. Zielgerichtete und bedeutungsvolle Betätigungen können stressbedingten Krankheiten entgegenwirken und das Risiko für Demenz reduzieren. Weiterführende Forschung über die Auswirkungen von Betätigung auf das Gehirn ist jedoch notwendig (Gutman & Schindler, 2007).
... In this study the changes in spectral power were investigated at seven electrodes: Fz, F3, F4, F7, F8, Cz and Pz. The rationale was that the effects of mental fatigue tend to gravitate towards midline and frontal electrodes in theta rhythm (Strijkstra, Beersma, Drayer, Halbesma, & Daan, 2003;Wascher et al., 2014); frontocentral and parietal regions for alpha (Cantero, Atienza, Salas, & Gómez, 1999;Oken, Salinsky, & Elsas, 2006;Santamaria & Chiappa, 1987), and frontal regions for the beta spectral band (Craig et al., 2012). ...
Article
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Background. Mental fatigue is a state of tiredness, decreased motivation, and increased aversion to performing a task. Mental fatigue is associated with the length of engagement in an activity (time-on-task) and the degree of cognitive e ort required. In addition, mental fatigue can be affected by personality characteristics, such as trait or domain-specific anxiety. ere is a lack of research into associations between mental fatigue and trait anxiety, as well as specific types of anxiety such as math anxiety. Objective. This study investigates whether the level of mental fatigue manifested in an EEG taken during the performance of a mixed problem-solving task, is associated with math and trait anxiety. Design. An EEG recording was performed on participants in a resting state with their eyes closed in two runs, both before and after they performed a task. e task consisted of three types of stimuli: arithmetic, algebraic, and lexical. Results. The results showed that the EEG correlates of fatigue changed be- tween the first and second runs. These changes were not linked with mathematics anxiety. Some significant EEG effects were found for trait anxiety: people with high trait anxiety appeared more aroused and showed less fatigue effects. However, these results did not reach the level of significance after correction for multiple comparisons. Conclusion. Overall, our results are in line with the motivational control theory, according to which mental fatigue “resets” when a person switches from one task to another. In our study, the experimental paradigm consisted of three types of tasks, a format which might have prevented fatigue. We discuss the implications of the study for further research into the links between anxiety and mental fatigue.
... Moreover, a reduction in vigilance might have caused a loss of association or connectivity between posterior brain regions, as these areas (occipital and parietal region) are affected by changes in the arousal level. Previous studies [14,26,28,29] have also reported that coherence varies between the alert and drowsy states. However, our in-depth analysis of inter-and intrahemispheric coherence in various brain regions generalizes the notion that coherence can be used to determine the physiological state of the driver. ...
... For example, other than focusing only on EEG power spectral analysis, EEG coherence (Achermann & Borbély, 1998) could be included in the analysis of the study. Some researchers used EEG coherence to investigate different arousal level in the rapid eyes movement and the wakefulness condition (Cantero, Atienza, Salas, & Gómez, 1999). As the Eysenck theory stated that introverts and extroverts have different arousal level, the EEG coherence therefore can be suitable for EEG studies of extraversion personality as well. ...
Article
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According to psychological studies, the most fundamental personality is the extraversion personality. Most studies looking at differences between extroverts and introverts are pen and paper based studies. However, in a few studies, electrophysiological signals were involved. In this paper, we reviewed studies examining extraversion personality using electroencephalography (EEG) and event-related potentials (ERP). It was found that some of the EEG studies claimed that extroverts and introverts can be differentiated using baseline EEG, while some others claimed otherwise. Conflicting findings were also observed in the ERP studies; higher/lower P300 amplitude in extroverts compared to that of introverts in visual stimuli tasks. These various findings are probably due to differences in their experimental protocols, sample size, or age of subjects. Other possible reasons include no consideration given on the main feature of extraversion and the studies only focused on EEG power spectral analysis. We are thus suggesting for future investigations to involve the main feature such as sociability and/or to incorporate more EEG features in the analysis to produce more robust and reliable results. This review constitutes a guidance for research on brain-related conditions of extroverts and introverts and shall be useful in many areas.
... It has been demonstrated that fronto-occipital and interfrontal coherence in the alpha band may discern the brain functional states related to different arousal levels [14]. The alpha coherence map obtained for the type 1 manipulation suggests that a dissociative strategy engages an extensive functional connectivity across all brain areas. ...
... mu rhythm, slow cortical potentials, spectral power ratios between different frequencies) have been used as a target for EEG-Neurofeedback (Huster et al., 2014). More recently, coherence that estimates the degree of similarity between two signals in the frequency domain (Guevara et al., 2011) and considered as an indicator of neuronal functional connectivity (Montplaisir et al., 1990;Koeda et al., 1995;Cantero et al., 1999;Nolte et al., 2004;Leocani et al., 2007;Srinivasan et al., 2007;Di Pino et al., 2012;Dubovik et al., 2012;Pellegrino et al., 2012;Tombini et al., 2012;Van Schependom et al., 2014) has been proposed as a target for neurofeedback (Sacchet et al., 2012;Hassan et al., 2015;Mottaz et al., 2015;von Carlowitz-Ghori et al., 2015). ...
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Objective: To investigate the EEG-derived functional connectivity at rest (FCR) patterns of fatigued Multiple Sclerosis (MS) patients in order to find good parameters for a future EEG-Neurofeedback intervention to reduce their fatigue symptoms. Methods: We evaluated FCR between hemispheric homologous areas, via spectral coherence between pairs of corresponding left and right bipolar derivations, in the Theta, Alpha and Beta bands. We estimated FCR in 18MS patients with different levels of fatigue and minimal clinical severity and in 11 age and gender matched healthy controls. We used correlation analysis to assess the relationship between the fatigue scores and the FCR values differing between fatigued MS patients and controls. Results: Among FCR values differing between fatigued MS patients and controls, fatigue symptoms increased with higher Beta temporo-parietal FCR (p=0.00004). Also, positive correlations were found between the fatigue levels and the fronto-frontal FCR in Beta and Theta bands (p=0.0002 and p=0.001 respectively). Conclusion: We propose that a future EEG-Neurofeedback system against MS fatigue would train patients to decrease voluntarily the beta coherence between the homologous temporo-parietal areas. Significance: We extracted a feature for building an EEG-Neurofeedback system against fatigue in MS.
... These previous studies also reported an increase in the mean global absolute power of alpha in the eyes-closed condition. An increase in alpha waves at the frontal region has been associated with a relaxation in healthy adults [17]. This finding in our study suggests that participants were more relaxed in the VO condition. ...
Conference Paper
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Electroencephalography (EEG) and centre of pressure (COP) data were recorded in young adults for 60 seconds during standing in visual transparent (VT) and visual occlusion (VO) conditions. In both of these conditions, participants wore VO liquid crystal spectacles which allowed the experimenter to accurately control visual information being presented or occluded to the participant. Alpha band (8-13 Hz) revealed significant differences in channel-averaged power spectrum in these two conditions, but not theta band (4-8 Hz) and beta band (13-30 Hz). In order to determine which channels contributed to these bands, region-averaged and single-channel power spectrum were computed which revealed similar patterns for eyes-open (VT) and eyes-closed (VO) conditions in each band. COP analysis was performed to understand postural steadiness in VT and VO conditions; the analysis indicated significant and larger time-domain distance measures (mean velocity), time-domain hybrid measures (mean frequency and sway area) and frequency domain measures (centroidal frequency) in the VO condition. The increased of alpha power in most frontal and posterior regions was indicative of the cortical processing of vision.
... After SD, alpha synchronization was decreased during eyes-closed resting state. A decrease in alpha coherence has been related to drowsiness [Cantero et al., 1999[Cantero et al., , 2000]. However, one has to realize that the methodology of the studies by Cantero et al. are systematically different from ours: (1) they acquired the different vigilance states (awake-drowsiness-REM sleep) while the subjects went to sleep; this setting is different from the AAT in our study where subjects sit upright and have to fixate on a black circle on a computer screen; (2) drowsiness was specifically specified when ''slow eye movements appeared simultaneously with alpha activity,'' whereas in our current study we excluded epochs with slow eye movements; ...
... In previous EEG studies, EEG coherence change was related to several functional cognitive activities, e.g. intelligence [16], memory efficiency [17][18] and arousal level [19]. Increased alpha coherence in meditation was found in many previous studies [e.g. ...
Article
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Almost all religions incorporate some form of meditation. Muslim prayer is the meditation of Islam. It is an obligatory prayer for all Muslims that is performed five times a day. Although a large body of literature exists on EEG changes in meditation, to date there has been no research published in a peer-reviewed journal on EEG changes during Muslim prayer. The purpose of this pilot study is to encourage further investigation on this type of meditation. Results of EEG analysis in twenty-five trials of Muslim prayer are reported. Some of the findings are consistent with the majority of the previous meditation studies (alpha rhythm slowing, increased alpha rhythm coherence). However, Muslim prayer does not show an increase in alpha and/or theta power like most of the results of other meditation studies. The possible cause of this discrepancy in meditation-related studies is highlighted and a systematic and standardised roadmap for future Muslim prayer EEG research is proposed.
... Con relación a la implicación neurológica de la actividad, las ocupaciones se pueden agrupar en tres categorías: aquellas que activan el sistema cerebral de recompensa, las que promueven una respuesta de relajación, y aquellas que preservan la función cognitiva en edades avanzadas (1,2). Respecto a las primeras, las que activan el sistema cerebral de recompensa (3), es sabido que actúan predominantemente sobre los neurotransmisores dopamina (4,5) y glutamato (6), los cuales juegan un papel fundamental en la realización de actividades placenteras (7), como actividades musicales o el dibujo, donde se comprobó que los sujetos de un estudio eran capaces de generar ondas beta y theta cuando dibujaban -es interesante anotar que las ondas beta se producen al realizar conscientemente actividades cotidianas, las alfa en estados de relajación, y las ondas theta y delta (predominantes durante el sueño) se presentan cuando el individuo participa de actividades que requieren una profunda concentración (8,9) y concretamente en actividades como dibujar o escribir-. A finales de los años 80 se describe el estado por el cual las personas experimentan profundos sentimientos de gratificación y de euforia como respuesta a participar en actividades altamente deseadas, estado que teóricamente resultaría de la activación del sistema de recompensa y de un incremento en los niveles de dopamina (10). ...
Article
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Objectives: To determine if an occupational therapy based intervention focused on performance reorganization on patients with rheumatoid arthritis reduces pain and improves selfefficacy and quality of life. Material and methods: Randomized controlled intervention study through a group program of seven occupational therapy sessions, conducted in five weeks. Results: We found an improvement in self-efficacy (p<0,001) and quality of life scores (p = 0,001, p = 0,08), as well as pain intensity MPQ (McGill Pain Questionnaire) measures, although the values collected with VAS (visual analogue scale) maintained over time. Conclusions: The program was effective in changing the studied variables, although a new study with a larger sample is required.
... 2). Такие изменения указывают на доминирование в первую очередь общеактивационных процессов с определенным торможением внутренней ментальной активности (затруднения top-down activity) [3] и снижением уровня наблюдательности (внешнего контроля) [19]. ...
... Con relación a la implicación neurológica de la actividad, las ocupaciones se pueden agrupar en tres categorías: aquellas que activan el sistema cerebral de recompensa, las que promueven una respuesta de relajación, y aquellas que preservan la función cognitiva en edades avanzadas (1,2). Respecto a las primeras, las que activan el sistema cerebral de recompensa (3), es sabido que actúan predominantemente sobre los neurotransmisores dopamina (4,5) y glutamato (6), los cuales juegan un papel fundamental en la realización de actividades placenteras (7), como actividades musicales o el dibujo, donde se comprobó que los sujetos de un estudio eran capaces de generar ondas beta y theta cuando dibujaban -es interesante anotar que las ondas beta se producen al realizar conscientemente actividades cotidianas, las alfa en estados de relajación, y las ondas theta y delta (predominantes durante el sueño) se presentan cuando el individuo participa de actividades que requieren una profunda concentración (8,9) y concretamente en actividades como dibujar o escribir-. A finales de los años 80 se describe el estado por el cual las personas experimentan profundos sentimientos de gratificación y de euforia como respuesta a participar en actividades altamente deseadas, estado que teóricamente resultaría de la activación del sistema de recompensa y de un incremento en los niveles de dopamina (10). ...
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Objetivos: determinar si una propuesta de intervención experimental desarrollada desde el campo de trabajo de la terapia ocupacional, dirigida a la reestructuración del desempeño ocupacional en pacientes con artritis reumatoide, reduce los niveles de dolor percibidos y mejora la autoeficacia y la calidad de vida de los mismos. Esta intervención se llevó a cabo de forma grupal, utilizando modelos de formación y enseñanza de estrategias a los pacientes. Material y método: estudio de intervención controlado aleatorizado de un programa grupal de terapia ocupacional de siete sesiones, de dos horas cada una, realizadas en cinco semanas. Resultados: se detectó una mejora en las puntuaciones de autoeficacia (p < 0,001) y de calidad de vida (p = 0,001; p = 0,08), así como de las puntuaciones de intensidad de dolor medidas con MPQ (McGill Pain Questionnaire), aunque los valores recogidos con EVA (escala visual analógica) se mantienen en el tiempo. Conclusiones: el programa resultó eficaz en la modificación de las variables estudiadas, apreciándose cambios significativos tanto en intensidad de dolor, como en los valores referidos a autoeficacia y calidad de vida. Es recomendable repetir el trabajo con una muestra mayor que permita obtener datos más consistentes.
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Mind-blanking (MB) is the inability to report mental events during unconstraint thinking. Previous work shows that MB is linked to decreased levels of cortical arousal, indicating dominance of cerebral mechanisms when reporting mental states. What remains inconclusive is whether MB can also ensue from autonomic arousal manipulations, pointing to the implication of peripheral physiology to mental events. Using experience-sampling, neural, and physiological measurements in 26 participants, we first show that MB was reported more frequently in low arousal conditions, elicited by sleep deprivation. Also, there was partial evidence for a higher number of MB reports in high arousal conditions, elicited by intense physical exercise. Transition probabilities revealed that, after sleep deprivation, mind-wandering was more likely to be followed by MB and less likely to be followed by more mind-wandering reports. Using classification schemes, we show higher performance of a balanced random forest classifier trained on both neural and physiological markers in comparison to performance when solely neural or physiological were used. Collectively, we show that both cortical and autonomic arousal affect MB report occurrences. Our results establish that MB is supported by combined brain-body configurations, and, by linking mental and physiological states they pave the way for novel, embodied accounts of spontaneous thinking.
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Neuroelectric and imaging studies of meditation are reviewed. Electroencephalographic measures indicate an overall slowing subsequent to meditation, with theta and alpha activation related to proficiency of practice. Sensory evoked potential assessment of concentrative meditation yields amplitude and latency changes for some components and practices. Cognitive event-related potential evaluation of meditation implies that practice changes attentional allocation. Neuroimaging studies indicate increased regional cerebral blood flow measures during meditation. Taken together, meditation appears to reflect changes in anterior cingulate cortex and dorsolateral prefrontal areas. Neurophysiological meditative state and trait effects are variable but are beginning to demonstrate consistent outcomes for research and clinical applications. Psychological and clinical effects of meditation are summarized, integrated, and discussed with respect to neuroimaging data.
Article
The effect of explicit interoception manipulation on electrophysiological (EEG) patterns concurrent with an interpersonal motor synchronization task with a social purpose was investigated in this study. Thirty healthy individuals executed a task involving behavioral motor synchronization with a social framing in both focus (conceived as the focus on the breath for a specific time interval) and no focus conditions. During the task, a 15 active electrodes electroencephalogram was used to record the following frequency bands (delta, theta, alpha, and beta band) from the frontal, temporo-central, and parieto-occipital regions of interest (ROIs). According to the results, for all the frequency bands significant higher mean values were found in the focus compared to no focus condition in the parieto-occipital ROI. On the whole, the current work conveys that when a motor synchronization task is executed and the person concurrently pays attention to his/her body correlates, EEG brain activity is empowered and boosted in posterior areas at the basis of attention to visceral signals, but also interpersonal action coordination. This evidence could have potentially interesting implications because it suggests the importance of modern breath-work during all conditions that require a social motor joint task, such as physiotherapy exercises or synchronized sports.
Chapter
Recognizing emotions based on brain activity has become crucial for understanding diverse human behavior in daily life. The electroencephalogram (EEG) has been proven to help gather information regarding the distribution of waveforms across the scalp. This project serves two goals. Firstly is to examine the synchronization and connectivity indices for emotion recognition. Secondly is to develop a framework to study the relationship between emotional state and brain activity based on synchronization and functional connectivity. The EEGs of 23 healthy volunteers were recorded while they viewed 18 film clips. To investigate the synchronization between various brain regions, a hybrid technique combining empirical mode decomposition with wavelet transform (EMD − WT) was employed. Linear features like cross-correlation (xCorr), coherence (Coh), and phase lag index (PLI) as well as nonlinear features like cross fuzzy entropy (CFuzzEn) and joint permutation entropy (JPE) were computed to capture various dynamical properties from emotion-based multi-channel EEG signals. Then, in order to increase the classification accuracy of various emotional states, choose features based on statistical analysis. At the end, the classifying process was utilized using the k-nearest neighbours (kNN) classifier. The classification results demonstrated the impact of the combination of CFuzzEn and JPE features as a remarkable synchronization index for analyzing emotions derived from an EEG-based data set. As a result, EEG indices enable a more thorough knowledge of the varied impacts of brain therapies on behavioral outcomes in humans.
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Neuroimaging evidence suggests that the frontal eye field (FEF) and inferior frontal junction (IFJ) govern the encoding of spatial and non-spatial (such as feature- or object-based) representations, respectively, both during visual attention and working memory tasks. However, it is still unclear whether such contrasting functional segregation is also reflected in their underlying functional connectivity patterns. Here, we hypothesized that FEF has predominant functional coupling with spatiotopically organized regions in the dorsal ('where') visual stream, whereas IFJ has predominant functional connectivity with the ventral ('what') visual stream. We applied seed-based functional connectivity analyses to temporally high-resolving resting-state magnetoencephalography (MEG) recordings. We parcellated the brain according to the multimodal Glasser atlas and tested, for various frequency bands, whether the spontaneous activity of each parcel in the ventral and dorsal visual pathway has predominant functional connectivity with FEF or IFJ. The results show that FEF has a robust power correlation with the dorsal visual pathway in beta and gamma bands. In contrast, anterior IFJ (IFJa) has a strong power coupling with the ventral visual stream in delta, beta, and gamma oscillations. Moreover, while FEF is phase-coupled with the superior parietal lobe in the beta band, IFJa is phase-coupled with the middle and inferior temporal cortex in delta and gamma oscillations. We argue that these intrinsic connectivity fingerprints are congruent with each brain region's function. Therefore, we conclude that FEF and IFJ have dissociable connectivity patterns that fit their respective functional roles in spatial vs. non-spatial top-down attention and working memory control.
Chapter
Neuroscientific approaches have become increasingly important in understanding how our bodies respond emotionally and physically to experiences. The use (and abuse) of neuroscience and psychological research methodologies for measuring emotional response has become a hot topic in research, particularly in applied sciences such as consumer and market research, often called “applied neuroscience.” Neuro- and psychological science can help researchers better understand unconscious motivators and emotional reactions. However, the application of these tools has been plagued with pseudoscience and “neuro-hype.” Researchers have experienced some disappointments when trying to incorporate these measures into their research. In this chapter we will discuss popular neuro-tools used to assess emotion. We will explore the challenges and discuss real examples of misuses, abuses, and disappointments in the application of these methodologies. Real and thoughtful applied neuroscience is about using the right combination of sensitive measures from psychology and neuroscience in the most appropriate ways.
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The vigilance decrement in performance is a significant operational issue in various applied settings. Psychophysiological methods for diagnostic monitoring of vigilance have focused on power spectral density measures from the electroencephalogram (EEG). This article addresses the diagnosticity of an alternative set of EEG measures, coherence between different electrode sites. Coherence metrics may index the functional connectivity between brain regions that supports sustained attention. Coherence was calculated for seven pre-defined brain networks. Workload and time-on-task factors primarily influenced alpha and theta coherence in anterior, central, and inter-hemispheric networks. Individual differences in coherence in inter-hemispheric, left intro-hemispheric and posterior networks correlated with performance. These findings demonstrate the potential applied utility of coherence metrics, although several methodological limitations and challenges must be overcome.
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Background: The aim of the study was to examine the characteristics of alpha wave peak frequency, power, and coherence in patients with schizophrenia. Methods: Thirty-one patients with schizophrenia and age- and sex-matched subjects with no psychopathology were enrolled. All study participants underwent quantitative electroencephalography (QEEG). Alpha-related values, including peak frequency, power, and coherence, were evaluated. Results: Alpha peak frequency on the Oz area was slower in the schizophrenia group than that in the control group. However, no differences in absolute or relative power were observed between the two groups. Significant reductions in absolute and relative coherence were observed at the C3-C4 and T3-T4 nodes in the patients with schizophrenia. Relative coherence was reduced at the P3-P4 nodes. Conclusion: This study focused on alpha variables detected in QEEG as intrinsic values to distinguish schizophrenia from a healthy control. The results suggest decreased alpha peak frequency of the occipital lobe and decreased coherence between the two hemispheres in patients with schizophrenia. A further study could elucidate the causal relationship and biological meaning of the variations in alpha waves in patients with schizophrenia.
Article
Women who adopt babies show caring behaviors and respond to stimuli from their infants just as biological mothers do, but several studies have shown that the cerebral functionality of biological mothers (BM) and adoptive mothers (AM) changes in relation to the type and emotional mean of the stimuli they receive from their babies. The complex perception and processing of different stimuli with emotional content (such as those emitted by babies) require functional synchronization among different cortical and subcortical brain areas. To determine whether the degree of functional synchronization between cortices varies when they perceive such stimuli, this study characterized the degree of cortical electroencephalographic (EEG) synchronization (correlation) among prefrontal, temporal and parietal areas in BM, AM and non-mothers while listening to a recording of a baby crying. BM showed a decreased EEG synchronization between the prefrontal and temporal cortices that may indicate a decrease in the modulatory control that the former exerts on the posterior cortices, and could be associated with deeper emotional involvement and increased sensitivity to the baby crying. The AM, in contrast, had higher degree of EEG synchronization between cortical areas in both hemispheres, likely associated with a greater modulation of the affective information of the crying baby, which allowed them to perceive it as less unpleasant. These data enrich our knowledge of the neurofunctional changes involved in motherhood, and of the neural processes that allow mothers (biological and adoptive) to be sensitive to their infants’ cues and respond appropriately.
Chapter
Meditation affects the brain rhythm significantly. Compared with non-meditators, the power of delta band was lower while high frequency band was higher for a meditator. Alpha band over the scalp was much more active in normal state for meditator with decreased dominant alpha frequency. Obvious transient process between normal eyes-closed rest and meditation was observed after EEG analysis. The active time and the power of beta and gamma band increased significantly in meditation. The inter-hemispheric and intra-hemispheric coherence beta and low gamma bands for meditative state were higher than normal state.
Article
The study of cerebral rhythms is possible by analyzing its electrophysiological features with quantitative EEG techniques. In the cases in which the same activity appears spontaneously in different brain states, the study of its electrophysiological features would help to establish functional differences associated to each of these states. The present work reviews those studies that determined the electrophysiological features of the different normal variants of alpha activity appearing in the wake-sleep continuous, more specifically, during relaxed wakefulness, drowsiness and REM sleep. The results indicate that each normal variant of alpha activity, in spite of showing a similar topographical distribution in each of the brain states, shows different features in relation to its spectral composition, functional relationships among cortical regions, and underlying brain micro-states. According to these experimental findings, each alpha variant would play a different brain function. Thus, the wakefulness alpha rhythm seems to reflect a maximum neuronal synchronization due to the absence of visual processing, whereas alpha activity during the drowsiness period would be associated with the brain processing of hypnagogic imagery happening at sleep onset. However, spontaneous alpha bursts of REM sleep would reflect the contact between the sleeping brain and the environment. This electrophysiological characterization has its most direct applied field in the design of algorithms to stage sleep automatically, as well as in the diagnosis and evaluation of clinical entities in which the brain generator mechanisms of this activity could be affected through the wake-sleep continuous.
Article
Background: Significant widespread differences in hemodynamics and electrodynamics between states of rest with open and closed eyes (default mode brain states) probably are consequences of involuntary shifts between interoceptive and exteroceptive modes of attention. These results make grounds for searches of similar correlates in active mental states. Results of such an attempt applied to states of verbal memorization and recollection using quantitative state-related EEG are presented. Methods: Electroencephalograms were recorded in 88 subjects in a resting state with the eyes opened (state EO), during memorization (state M) of verbal bilingual semantic pairs (Latin and Russian), presented on a screen, and during recollection (state R) of the learned information Statistical comparison of the EEG spectral power (local synchronization) and coherence (spatial synchronization) in the frequency bands theta, alpha1, apha2, beta1, beta2 and gamma showed that induction of the states M and R led to multiple significant changes in the EEG absolute power and coherence as compared to the state EO and as compared between active states R and M. Results: The results demonstrate that mnestic states of memorization and recollection are catered with rather different brain functional states reflected in system reorganizations of brain electrodynamics on the levels of local and spatial synchronizations both. Conclusion: The observed differences can be related to changes of the exteroceptive- introceptive attention balance.
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EEG coherence analysis was used to study aspects of the synchronisation of electrical processes in the left and right cerebral hemispheres of right-handed and left-handed healthy subjects in a state of calm wakefulness. Right-handed subjects showed a greater coherence in the left hemisphere and left-handed subjects in the right hemisphere. There were also differences between right-handed and left-handed subjects in the regional profiles of interhemispheric asymmetry and in the interhemispheric asymmetry of individual spectral bands. These differences may reflect variations in the involvement of cortical and subcortical cerebral structures in the formation of the hemispheric specificity. Changes in interhemispheric coherence with the onset of drowsiness were also observed. This suggests that changes in the interconnections of neural networks are also involved in changes in arousal. Certain characteristic regional interhemispheric asymmetry patterns and asymmetries in the spectral bands appear to be necessary for normal human brain function.
Book
Electroencephalography (EEG) is practiced by neurologists, cognitive neuroscientists, and others interested in functional brain imaging. Whether for clinical or experimental purposes, all studies share a common purpose-to relate scalp potentials to the underlying neurophysiology. Electrical potentials on the scalp exhibit spatial and temporal patterns that depend on the nature and location of the sources and the way that currents and fields spread through tissue. Because these dynamic patterns are correlated with behavior and cognition, EEG provides a "window on the mind," correlating physiology and psychology. This classic and widely acclaimed text, originally published in 1981, filled the large gap between EEG and the physical sciences. It has now been brought completely up to date and will again serve as an invaluable resource for understanding the principles of electric fields in living tissue and for using hard science to study human consciousness and cognition. No comparable volume exists for it is no easy task to explain the problems of EEG in clear language, with mathematics presented mainly in appendices. Among the many topics covered by the Second Edition are micro and meso (intermediate scale) synaptic sources, electrode placement, choice of reference, volume conduction, power and coherence measures, projection of scalp potentials to dura surface, dynamic signatures of conscious experience, neural networks immersed in global fields of synaptic action, and physiological bases for brain source dynamics. The Second Edition is an invaluable resource for neurologists, neuroscientists (especially cognitive neuroscientists), biomedical engineers, and their students and trainees. It will also appeal to physicists, mathematicians, computer scientists, psychiatrists, and industrial engineers interested in EEG.
Article
The question of the intracortical sources of the alpha activity of the EEG has been investigated in dogs, using intracortical electrodes placed along a direction perpendicular to the cortical surface. Alpha rhythms have been quantified using spectral analysis, namely the phase relationships between alpha activities recorded between several electrodes has been computed. It was demonstrated that opposition of phase exists between alpha rhythms recorded at different depths within the visual cortex. The phase reversal (180 degrees ) was found at about 1100 mum below the cortical surface. The neurophysiological basis of such alpha activity is discussed.
Article
A method of modified coherence analysis was applied to the interpretation of EEG differences between the frontal and occipital cortex. This paper discusses a bidirectional communication model for the frontal and occipital cortex. Directed coherence method was used to analyze alpha activities over the scalp. The results show that both in the left and right hemisphere, slow waves in the alpha frequency band had high correlation in the frontal-occipital direction, and fast waves had high correlation in the occipital-frontal direction. It may suggest that the structure of information transmission is different for fast and slow waves of alpha rhythm.
Article
Measures of interhemispheric EEG coherence during REM and NREM sleep reflect the functional connectivity of the right and left hemispheres mediated by the corpus callosum. Surface recordings of interhemispheric coherence in two patients reflected fairly accurately the degree of anatomical section produced by partial callosotomy. With further development, EEG coherence may prove useful as a noninvasive method for assessing interhemispheric integration under different physiological and experimental conditions.
Article
Source determination of alpha activity was studied using the relative power contribution analysis (RPCA) method which allows determination of the relative contributions of different areas to the power of a certain area at different frequencies. In 20 normal subjects, EEGs were recorded from F3, F4, C3, C4, P3, P4, O1 and O2, each referenced to a linked ear. An 8-dimensional autoregressive model was fitted to the EEGs of 10.24 sec. Based on the model, RPCA was performed. For each area, alpha activity was divided into two parts: one originating in its own area (endogenous) and another in the other areas (exogenous). Endogenous alpha activity increased as the area was more posterior. In the anterior regions (frontal and central), endogenous alpha power (power of endogenous alpha activity) was small, while exogenous alpha power was large. In the posterior regions (parietal and occipital), the amount of endogenous alpha power did not differ markedly from that of exogenous alpha power. The posterior regions, which generate more endogenous alpha activity, can be considered to play a dominant role in alpha generating mechanisms. In some subjects, alpha generators with a different frequency from that of the occipital areas were observed.
Article
EEG coherence was computed from 19 scalp locations from 189 children ranging in age from 5 to 16 years. Tests of spatial homogeneity of EEG coherence were conducted by comparing EEG coherence as a function of different interelectrode distances in the anterior-to-posterior versus posterior-to-anterior directions. Highly significant inhomogeneities were observed since greater coherence was present in the anterior-to-posterior direction than in the posterior-to-anterior directions. Greater coherence was also present in frontal derivations than in posterior derivations and from the right hemisphere in comparison to the left hemisphere. These data indicate that at least two separate sources of EEG coherence were present (1) coherence produced through the action of short length axonal connections, and (2) coherence produced through the action of long distance connections. Measures of phase delays as a function of interelectrode distance supported the development of a 'two-compartmental' model of EEG coherence in which different features of coherence are produced by different length fiber systems. Based on this model a number of hypotheses were developed to explain differences in connectivity between left and right hemispheres and frontal versus occipital cortex.
Article
A theory of neocortical interactions is developed involving both local delays (PSP rise and decay times) and global delays due to finite velocity of action potentials in corticocortical fibers. The theory is based on plausible assumptions regarding input/output relations in neocortical columns and realistic neural parameters. The simultaneous existence of short wavelength waves propagating away from multiple epicenters and long wavelength standing waves due to global boundary conditions is predicted. Both phenomena appear to have dominant oscillation frequencies in the general range of observed EEG phenomena in humans. A mechanism by which removal of diffuse input from the reticular formation may cause an abrupt drop in EEG frequency (as in the transition from the awake to sleeping state) is postulated.
Article
The topographic EEG features of drowsiness and sleep onset are much less well documented than are their temporal aspects. A commercial topographical mapping system was used to assess the main EEG features employing all 19 international 10/20 system electrode sites referenced to linked ears during wakefulness, stages 1A and 1B drowsiness, stage 2 sleep, and sleep onset REM periods in 19 patients. All patients had been referred for a diagnostic EEG or a Multiple Sleep Latency Test and had essentially normal EEGs. Anterior alpha of drowsiness seldom represented frontal spread of the occipital alpha rhythm but usually was a distinct activity of apparent separate origin. Theta activities of drowsiness were maximum at CZ and FZ. Vertex sharp waves and sawtooth waves of rapid eye movement (REM) sleep had similar fields maximum at the midline with a steep decrease laterally. Isolated anterior mainly negative waves were identified. Sleep spindles were usually maximal in fronto central, occasionally centro parietal, or even parietal areas.
Article
Dipole sources were investigated in 22 normal subjects with a variety of strategies available through the BESA program. When all the data were summed one regional source, located near the midline in the basal portions of the occipital lobe, explained 92% of the variance. Two regional sources, initially constrained for symmetry but subsequently freed from constraint placed them also in the occipital regions near the midline and reduced the residual variance to 4%. Pooled data obscure, however, the marked individual differences especially in regard to lateralization. In the individual case the major source was also always in one occipital area but its location, especially the degree of separation from the midline depended upon alpha distribution and the strategy used in the workup of the data. The orientation of the major components of the regional sources was usually in the posterior-anterior direction, fairly parallel to the midline and while the other one pointed to the upper convexity. Because of the considerable variability of the alpha rhythm in given subjects and even within the same individual a model which requires symmetry constraints is not optimal for all instances, even when constraints are lifted thereafter. The study demonstrated the feasibility of distinguishing predominantly mesial sources from those which are bihemipheric with more lateral origins but several different models may have to be used to reach the most realistic conclusions.
Article
Resting EEG interhemispheric and intrahemispheric coherences (ICoh and HCoh) in the theta, alpha and beta bands were studied in 7 patients with agenesis of the corpus callosum (5 children, aged 10-14 years, and 2 adults) and 2 groups of sex- and age-matched normal children and adults (42 subjects). In patients the ICohs (F3/F4, C3/C4, P3/P4, O1/O2) were lower than in the normal sample. The ICoh decrease, corresponding with the completeness of commissural agenesis, showed the essential role of the corpus callosum in interhemispheric EEG synchronization. A remarkable new fact was found, namely lower right hemisphere HCoh in the acallosal patients in comparison to the normals, suggesting reduced connectivity of the right hemisphere. It is assumed that the deviant HCoh patterns in the patients, most pronounced in the beta band, are indicative of compensatory left hemisphere mechanisms, accounting for a specific brain plasticity phenomenon in acallosal subjects.
Article
The present study was conducted to examine inter- and intrahemispheric EEG coherence in 14 healthy, right-handed adults during wakefulness and light drowsiness as assessed by eye movement and EEG activity. Interhemispheric coherence was significantly lower during light drowsiness than during wakefulness for O1-O2 in the alpha-1 band and for F3-F4 in the beta-1 band. Intrahemispheric EEG coherence was significantly higher during light drowsiness for C4-O2 in the theta-1 and beta-1 bands. These findings indicate that light drowsiness can alter both inter- and intrahemispheric EEG coherence when compared with wakefulness, suggesting that cerebral functional organization changes during light drowsiness. It is important, therefore, to control arousal level of subjects in future studies dealing with the relationship between EEG coherence and various pathological conditions.
Article
Animal studies have shown that the sleep-related oscillations in the frequency range of spindles and slow-waves, and in the gamma band occur synchronously over large parts of the cerebral cortex. Coherence analysis was used to investigate these oscillations in the human sleep electroencephalogram. In all-night electroencephalogram recordings from eight young subjects power and coherence spectra within and between cerebral hemispheres were computed from bipolar derivations placed bilaterally along the antero-posterior axis. The 0.75-50 Hz range was examined with a resolution of 0.25 Hz. Distinct peaks in coherence were present in non-rapid eye movement sleep but not in rapid eye movement sleep. The most prominent and consistent peak was seen in the range of sleep spindles (13-14 Hz), and additional peaks were present in the alpha band (9-10 Hz) and low delta band (1-2 Hz). Whereas coherence in the spindle range was highest in stage 2, the alpha peak was most prominent in slow-wave sleep (stages 3 and 4). Interhemispheric coherence at 30 Hz was higher in rapid eye movement sleep than in non-rapid eye movement sleep. There were also marked sleep state-independent regional differences. Coherence between homologous interhemispheric derivations was high in the low frequency range and declined with increasing frequencies, whereas coherence of intrahemispheric and non-homologous interhemispheric derivations was at a low level throughout the spectra. It is concluded that coherence analysis may provide insights into large-scale functional connectivities of brain regions during sleep. The high coherence of sleep spindles is an indication for their widespread and quasi-synchronous occurrence throughout the cortex and may point to their specific role in the sleep process.
Article
In a study with 10 young, healthy subjects, alpha activities were studied in three different arousal states: eyes closed in relaxed wakefulness (EC), drowsiness (DR), and REM sleep. The alpha band was divided into three subdivisions (slow, middle, and fast) which were analyzed separately for each state. The results showed a different spectral composition of alpha band according to the physiological state of the subject. Slow alpha seemed to be independent of the arousal state, whereas middle alpha showed a difference between REM and the other states. The fast-alpha subdivision appears mainly as a waking EEG component because of the increased power displayed only in wakefulness and lower and highly stable values for DR and REM. Scalp distribution of alpha activity was slightly different in each state: from occipital to central regions in EC, this topography was extended to fronto-polar areas in DR, with a contribution from occipital to frontal regions in REM sleep. These results provide evidence for an alpha power modulation and a different scalp distribution according to the cerebral arousal state.
Article
Spontaneous alpha activity clearly present in relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and REM sleep was studied with spatial segmentation methods in order to determine if the brain activation state would be modulating the alpha spatial microstates composition and duration. These methods of spatial segmentation show some advantages: i) they extract topographic descriptors independent of the chosen reference (reference-free methods), and ii) they achieve spatial data reduction that are more data-driven than dipole source analysis. The results obtained with this study revealed that alpha activity presented a different spatio-temporal pattern of brain electric fields in each arousal state used in this study. These differences were reflected in a) the mean duration of alpha microstates (longer in relaxed wakefulness than in drowsy period and REM sleep), b) the number of brain microstates contained in one second (drowsiness showed more different microstates than did relaxed wakefulness and REM state), and c) the number of different classes (more abundant in drowsiness than in the rest of brain states). If we assume that longer segments of stable brain activity imply a lesser amount of different information to process (as reflected by a higher stability of the brain generator), whereas shorter segments imply a higher number of brain microstates caused by more different steps of information processing, it is possible that the alpha activity appearing in the sleep onset period could be indexing the hypnagogic imagery self-generated by the sleeping brain, and a phasic event in the case of REM sleep. Probably, REM-alpha bursts are associated with a brain microstate change (such as sleep spindles), as demonstrated by its phasic intrusion in a desynchronized background of brain activity. On the other hand, alpha rhythm could be the "baseline" of brain activity when the sensory inputs are minimum and the state is relaxed wakefulness.
Article
Alpha activity attenuation (blocking) over occipital regions is an electrophysiological index of cortical activation associated with visual attention and waking mental imagery. The present work focused on exploring whether the human REM background alpha activity was modulated, attending to tonic- (without rapid oculomotor activity) and phasic-REM periods (with a prominent burst of REMs). The obtained results revealed that the background alpha activity showed a decreased spectral power over occipital brain regions during phasic-REM in comparison with tonic-REM periods. This result suggests an active visual processing caused by the complex mental imagery generated during periods of oculomotor activity in human REM sleep.
Relationships among signals: cross-spectral analysis of the EEG
  • Dumermuth
Dumermuth, G. and Molinari, L., Relationships among signals: cross-spectral analysis of the EEG. In R. Weitkunat (Ed.), Digital Biosignal Processing, Elsevier, Amsterdam, 1991, pp. 361±398.
The EEG of Drowsiness
  • J Santamaria
  • K H Chiappa
Santamaria, J. and Chiappa, K.H., The EEG of Drowsiness, Demos, New York, 1987.