EEG Investigation Research Articles

Study of clinical and etiological profile of new onset seizure in adults reporting to tertiary care centre, Mysore

Background: Overall incidence of seizure is found to be 0.2-0.6 per 1000 population per year. A first seizure mandates individual counselling about the risk of recurrence, the pros and cons of drug treatment. Seizures are usually a manifestation of an underlying pathology which may be genetic, structural or metabolic. Objectives of current study were to study the clinical profile of new onset seizures in adults (greater than 19 years) attending to tertiary care Centre, Mysore and to determine the etiology of new onset seizures in adults reporting to tertiary care centre, Mysore.Methods: All participants fulfilling the inclusion criteria were interviewed as per proforma. Participant’s demographic, social and medical details were recorded in proforma sheet and patients were subjected to neuroimaging studies, EEG and other necessary blood investigations. In all cases the seizure type is classified according to ILAE Classification 2017.Results: Among 100 cases evaluated for new onset, Majority of the patients were 41 to 60 years. Generalised seizures (95%) were more common than focal seizures.Among neurological etiological causes, vascular causes (34%) were most common. Most common Non-neurological cause for seizures was alcohol withdrawal (46.67%).Conclusions: If proper analysis of etiology is made, seizures can be treated accordingly thus reducing the morbidity and mortality associated with it. Primary care physicians play a pivotal role in identifying patients with adult onset seizures and should encourage these patients to undergo neuroimaging so as to arrive at an appropriate etiological diagnosis.

Rapid Handheld Continuous Electroencephalogram (EEG) Has the Potential to Detect Delirium in Older Adults.

Delirium-related biochemical derangements lead to electrical changes that can be detected in electroencephalographic (EEG) patterns followed by behavioral signs and symptoms. Studies using limited lead EEG show a large difference between patients with and without delirium while discriminating delirium from other causes. Handheld rapid EEG devices may be capable of detecting delirium before symptom onset, thus providing an objective physiological method to detect delirium when it is most amenable to interventions. The aim of this study was to explore the potential for rapid EEG to detect waveform pattern changes consistent with delirium status. This prospective exploratory pilot study used a correlational design and mixed models to explore the relationships between handheld portable EEG data and delirium status. While being under powered minimized opportunities to detect statistical differences in EEG-derived ratios using spectral density analysis, sleep-to-wake ratios tended to be higher in patients with delirium. Limited lead EEG may be useful in predicting adverse outcomes and risk for delirium in older critically ill patients. Although this population is at the highest risk for mortality, delirium is not easily identified by current clinical assessments. Therefore, further investigation of limited lead EEG for delirium detection is warranted.

Seizures Presenting as ADHD: A Case Report

ADHD (Attention Deficit Hyperactivity Disorder) is a neurodevelopmental disorder that affects a large proportion of children. ADHD is associated with an increased risk of seizures and is characterised by inattention, restlessness, and impatience.
 A 6-year-old boy with ADHD presented to the Psychiatry Out-Patient Department with complaints of aggressive behaviour and restlessness. Trademark symptoms such as difficulty in sustaining concentration, not following instructions, running about, not being able to sit in one place, and verbally and physically abusive behaviour were noted in the patient.
 Atomoxetine and Risperidone were prescribed for inattention and behavioural misconduct, respectively. Due to lack of improvement and a seizure suggestive incident an EEG investigation was instigated; it showed seizure activity for which Sodium Valproate was initiated for the same. Due to adverse effects, Oxcarbazepine was additionally included. Oxcarbazepine showed the most effective in treatment and progress continued with the intake of the drug. Currently, the boy is showing near total improvement and is on Atomoxetine 20 mg, Oxcarbazepine 600 mg and Sodium Valproate 400 mg, all of the above in divided doses.
 This case report aims at highlighting the manifestation of unprovoked seizure activity in a patient previously diagnosed with ADHD with conduct disorder.
 Several medical conditions in children mirror ADHD symptoms, making diagnosis difficult. For accurate treatment, it's crucial to rule out a differential diagnosis. With the help of this case, we can shed some light on the lack of knowledge and protocols in the management of hyperkinetic disorders, which has resulted in the spike of misdiagnosed cases across the country.

STXBP1 Syndrome Is Characterized by Inhibition-Dominated Dynamics of Resting-State EEG.

STXBP1 syndrome is a rare neurodevelopmental disorder caused by heterozygous variants in the STXBP1 gene and is characterized by psychomotor delay, early-onset developmental delay, and epileptic encephalopathy. Pathogenic STXBP1 variants are thought to alter excitation-inhibition (E/I) balance at the synaptic level, which could impact neuronal network dynamics; however, this has not been investigated yet. Here, we present the first EEG study of patients with STXBP1 syndrome to quantify the impact of the synaptic E/I dysregulation on ongoing brain activity. We used high-frequency-resolution analyses of classical and recently developed methods known to be sensitive to E/I balance. EEG was recorded during eyes-open rest in children with STXBP1 syndrome (n = 14) and age-matched typically developing children (n = 50). Brain-wide abnormalities were observed in each of the four resting-state measures assessed here: (i) slowing of activity and increased low-frequency power in the range 1.75–4.63 Hz, (ii) increased long-range temporal correlations in the 11–18 Hz range, (iii) a decrease of our recently introduced measure of functional E/I ratio in a similar frequency range (12–24 Hz), and (iv) a larger exponent of the 1/f-like aperiodic component of the power spectrum. Overall, these findings indicate that large-scale brain activity in STXBP1 syndrome exhibits inhibition-dominated dynamics, which may be compensatory to counteract local circuitry imbalances expected to shift E/I balance toward excitation, as observed in preclinical models. We argue that quantitative EEG investigations in STXBP1 and other neurodevelopmental disorders are a crucial step to understand large-scale functional consequences of synaptic E/I perturbations.

Electrophysiological Correlates of Social Decision-making: An EEG Investigation of a Modified Ultimatum Game.

Cooperation behaviors during social decision-making have been shown to be sensitive to manipulations of context. However, it remains unclear how aspects of context in dynamic social interactions, such as observed nonverbal behaviors, may modulate cooperation decisions and the associated neural mechanisms. In this study, participants responded to offers from proposers to split $10 in an Ultimatum Game following observation of proposer approach (friendly) or avoidance (nonfriendly) behaviors, displayed by dynamic whole-body animated avatars, or following a nonsocial interaction control condition. As expected, behavioral results showed that participants tended to have greater acceptance rates for unfair offers following observed nonverbal social interactions with proposers compared with control, suggesting an enhancing effect of social interactions on cooperative decisions. ERP results showed greater N1 and N2 responses at the beginning of social interaction conditions compared with control, and greater sustained and late positivity responses for observed approach and avoidance proposer behaviors compared with control. Event-related spectral perturbation (ERSP) results showed differential sensitivity within theta, alpha, and beta bands during observation of social interactions and offers that was associated with subsequent decision behaviors. Together, these results point to the impact of proposers' nonverbal behaviors on subsequent cooperation decisions at both behavioral and neural levels. The ERP and ERSP findings suggest modulated attention, monitoring, and processing of biological motion during the observed nonverbal social interactions, influencing the participants' responses to offers. These findings shed light on electrophysiological correlates of response to observed social interactions that predict subsequent social decisions.

Author Response: Clinical, Neuroimmunologic, and CSF Investigations in First Episode Psychosis.

We appreciate the interest in our research.1 According to Pollak and colleagues,2 criteria of possible autoimmune psychosis (AP) are fulfilled if a patient has abrupt onset psychotic symptoms with at least one of the following: the presence of a tumor, movement disorder (dyskinesias, catatonia), adverse response to antipsychotics, “severe or disproportionate” cognitive dysfunction, decreased level of consciousness, unexplained seizures, and significant autonomic dysfunction.2 Fulfilment of these criteria should lead to additional tests such as EEG, MRI, and serum or CSF investigations. In our series of 105 patients with first episode of psychosis (FEP), 20% fulfilled these criteria but never developed AP.1 We confirm that 2 of 3 patients with anti-N-methyl-d-aspartate receptor (anti-NMDAR) encephalitis presenting with FEP did not fulfill any of these criteria, including catatonia, which is a complex syndrome with its own set of 12 criteria that include echolalia.3 Thus, catatonia and echolalia should not be used as interchangeable terms.

P030 The effects of continuous positive airway pressure (CPAP) therapy in moderate to severe obstructive sleep apnea (OSA): A high-density electroencephalography (EEG) study

Abstract Introduction A previous high-density EEG investigation in OSA showed regional sleep EEG deficits particularly slow wave activity (SWA) in the parietal region. It is unclear whether CPAP treatment can reverse local sleep EEG abnormalities, and whether any recovery is related to improved cognitive function. Methods Fifteen males with moderate-severe OSA (age 50.4±6.5yrs, AHI 51.7±23.5/h) underwent polysomnography with 256-channel high-density EEG at baseline and following 3 months of CPAP. Tasks assessing cognitive performance and sleep-dependent memory were administered. Topographical spectral power maps were calculated for standard frequency ranges for sleep stages. Differences in normalized power between baseline and treatment were determined by statistical nonparametric mapping. Results In 11 CPAP compliant patients (data loss: intolerant of CPAP[n=3]/high-density EEG [n=1]), total sleep time did not change after CPAP but N1 (baseline vs. treatment: 66.9 vs. 39.5 mins, p=0.008) and N2 (195.0 vs. 150.6 mins, p=0.002) sleep was lower and N3 (89.8 vs. 128.7 mins, p=0.003) was higher. Topographic high-density EEG analysis revealed a regional increase in SWA (1–4.5Hz) during N3 sleep in a cluster of 22 electrodes overlying the parietal cortex (paired t-test, t(10)=-3.9, p=0.0029). The change in N3 SWA in the parietal cluster after CPAP was correlated with improved overnight procedural memory on the motor sequence task (rho=0.79, p=0.03) and better executive functioning (Stroop accuracy, rho=0.73, p=0.01). Conclusion CPAP treatment reduces localised deficits in sleep EEG, and specific regional recovery relates to short-term improvements in memory and executive function. These data also highlight the potential for long-term therapeutic effects on cognitive outcomes.

Rapid scene categorization is not purely feed-forward: An EEG investigation of scene gist facilitation by sequential predictions

Rapid scene categorization is not purely feed-forward: An EEG investigation of scene gist facilitation by sequential predictions

Cognitive perturbations affect brain cortical activity and postural control: An investigation of human EEG and motion data

Biomechanical analyses recognize the role of cognitive loads in postural stability by measuring body sway related parameters. However, the simultaneous investigation of the neural and motor behavior during control of the posture is limited. The present study investigated the effects of cognitive load addition on postural control and status of topographical brain activity in quiet and perturbed standing. Sixteen healthy young people participated in four main levels of the experiment, including two levels of physical difficulty with and without math questions in the form of mental calculations. Cortical electrical activity and postural sways were recorded simultaneously using a 19-channel electroencephalography and motion analysis method to measure body movements by a high-speed camera and active markers. Analysis of variance showed significant effects of the cognitive perturbation on theta band energy of the frontal (p < .001) and temporal (p = .030) regions. Approximate entropy metrics of the brain frontal activity and also the movements of the center of mass were reduced by cognitive loads (p < .05). The energy of theta band EEG signals was positively correlated to the overall mechanical work in easier tasks (r = 0.59), and the CoM stability metrics in the more difficult tasks (r > 0.57). Addition of the cognitive loads to a postural task reduced the stability by higher levels of brain cortex involvement. Addition of the second cognitive task to standing reduced the complexity of both neural and motor activities. The neuro-motor collaboration in maintenance of balance was interfered with the arithmetic cognitive loads.

Dealing with uncertainty: A high-density EEG investigation on how intolerance of uncertainty affects emotional predictions.

Intolerance of uncertainty (IU) can influence emotional predictions, constructed by the brain (generation stage) to prearrange action (implementation stage), and update internal models according to incoming stimuli (updating stage). However, neurocomputational mechanisms by which IU affects emotional predictions are unclear. This high-density EEG study investigated if IU predicted event-related potentials (ERPs) and brain sources activity developing along the stages of emotional predictions, as a function of contextual uncertainty. Thirty-six undergraduates underwent a S1-S2 paradigm, with emotional faces and pictures as S1s and S2s, respectively. Contextual uncertainty was manipulated across three blocks, each with 100%, 75%, or 50% S1-S2 emotional congruency. ERPs, brain sources and their relationship with IU scores were analyzed for each stage. IU did not affect prediction generation. During prediction implementation, higher IU predicted larger Contingent Negative Variation in the 75% block, and lower left anterior cingulate cortex and supplementary motor area activations. During prediction updating, as IU increased P2 to positive S2s decreased, along with P2 and Late Positive Potential in the 75% block, and right orbito-frontal cortex activity to emotional S2s. IU was therefore associated with altered uncertainty assessment and heightened attention deployment during implementation, and to uncertainty avoidance, reduced attention to safety cues and disrupted access to emotion regulation strategies during prediction updating.

Electrophysiological aftereffects of high-frequency transcranial random noise stimulation (hf-tRNS): an EEG investigation

There is evidence that high-frequency transcranial random noise stimulation (hf-tRNS) is effective in improving behavioural performance in several visual tasks. However, so far there has been limited research into the spatial and temporal characteristics of hf-tRNS-induced facilitatory effects. In the present study, electroencephalogram (EEG) was used to investigate the spatial and temporal dynamics of cortical activity modulated by offline hf-tRNS on performance on a motion direction discrimination task. We used EEG to measure the amplitude of motion-related VEPs over the parieto-occipital cortex, as well as oscillatory power spectral density (PSD) at rest. A time–frequency decomposition analysis was also performed to investigate the shift in event-related spectral perturbation (ERSP) in response to the motion stimuli between the pre- and post-stimulation period. The results showed that the accuracy of the motion direction discrimination task was not modulated by offline hf-tRNS. Although the motion task was able to elicit motion-dependent VEP components (P1, N2, and P2), none of them showed any significant change between pre- and post-stimulation. We also found a time-dependent increase of the PSD in alpha and beta bands regardless of the stimulation protocol. Finally, time–frequency analysis showed a modulation of ERSP power in the hf-tRNS condition for gamma activity when compared to pre-stimulation periods and Sham stimulation. Overall, these results show that offline hf-tRNS may induce moderate aftereffects in brain oscillatory activity.

Electroclinical markers to differentiate between focal and generalized epilepsies.

Generalized-onset seizures originate at a point within the brain and rapidly engage bilaterally distributed networks, whilst focal-onset seizures originate within networks limited to one hemisphere which may be discretely localized or more widely distributed. Challenges in data capturing have resulted in a lack of consistency across incidence and prevalence studies for estimates of generalized versus focal epilepsies in population groups, with a preponderance of unclassified cases. Infants and young children can further challenge delineation due to variable expression at different stages of brain maturation and impaired ability to express sensory seizure semiology. Focal seizures are divided into those in which the affected person is aware and those with impaired awareness; these events can be motor or non-motor. Generalized seizures are also categorized as motor and non-motor, but loss of awareness occurs with most events. Delineation between generalized and focal epilepsies is important for ongoing management. EEG, neuroimaging and other investigations (genetics, immune markers, etc.) can support the outcome but distinction between focal and generalized epilepsy in isolation is rarely achieved using such techniques. Certain clinical settings such as age, underlying aetiologies, and co-morbidities may be more predisposed to specific types of epilepsy. The differentiation between generalized and focal seizures remains a clinical process based on meticulous clinical history and examination, and is of relevance for the selection of antiseizure medications and identification of patients who may be viable for epilepsy surgery.

An EEG investigation of alpha and beta activity during resting states in adults with Williams syndrome

BackgroundWilliams syndrome (WS) is neurodevelopmental disorder characterised by executive deficits of attention and inhibitory processing. The current study examined the neural mechanisms during resting states in adults with WS in order to investigate how this subserves the attention and inhibitory deficits associated with the syndrome.MethodAdopting electroencephalography (EEG) methodology, cortical electrical activity was recorded from eleven adults with WS aged 35 + years during Eyes Closed (EC) and Eyes Open (EO) resting states, and compared to that of thirteen typically developing adults matched for chronological age (CA) and ten typically developing children matched for verbal mental ability (MA). Using mixed-design analyses of variance (ANOVA), analyses focused on the full alpha (8–12.5 Hz), low-alpha (8–10 Hz), upper-alpha (10–12.5 Hz), and beta (13–29.5 Hz) bands, as these are thought to have functional significance with attentional and inhibitory processes.ResultsNo significant difference in alpha power were found between the WS and CA groups across all analyses, however a trend for numerically lower alpha power was observed in the WS group, consistent with other developmental disorders characterised by attentional/inhibitory deficits such as Attention Deficit Hyperactivity Disorder (ADHD). In contrast, comparable beta power between the WS and CA groups during both EC/EO conditions suggests that their baseline EEG signature is commensurate with successful attentional processing, though this needs to be interpreted with caution due to the small sample size. Analyses also revealed an unusual trend for low variability in the EEG signature of the WS group, which contradicts the heterogeneity typically observed behaviourally.ConclusionsThis novel finding of low variability in the EEG spectra in the WS group has been previously associated with poor behavioural performance in ADHD and is highly informative, highlighting future research needs to also consider how the role of low variability in the EEG profile of WS manifests in relation to their behavioural and cognitive profiles.

What’s next? Neural correlates of emotional predictions: A high-density EEG investigation

Emotions were recently reconsidered as predictions, constructed by the brain (generation stage) to prearrange action (implementation stage), and update internal models according to incoming stimuli (updating stage). However, it is unclear how emotional predictions are shaped by stimuli predictability. This study investigated the role of stimuli predictability on emotional predictions through high-density EEG. Twenty-six undergraduates underwent a S1-S2 paradigm, with emotional faces as S1s and emotional pictures as S2s. Stimuli predictability was manipulated across three blocks, in which S1 valence was predictive of S2 in the 100%, 75%, or 50% of trials. ERPs and brain sources were analyzed for each stage. During prediction generation, a larger N170/superior temporal sulcus activity emerged to fearful faces in blocks with full (100%) and medium (75%) predictive ratios. During implementation, the random block (50%) elicited a valence-independent pre-allocation of resources, reflected by a larger CNV and activation of a wide left network. In the updating stage, emotional pictures always elicited a larger LPP, while a larger P2 to neutral stimuli and a higher activity of the orbitofrontal cortex signaled early valence-dependent and late block-dependent prediction errors. These findings provide the first evidence of how stimuli predictability shape each neurocomputational stage of emotional predictions construction.

Blink- and saccade-related suppression effects in early visual areas of the human brain: Intracranial EEG investigations during natural viewing conditions

Blinks and saccades, both ubiquitous in natural viewing conditions, cause rapid changes of visual inputs that are hardly consciously perceived. The neural dynamics in early visual areas of the human brain underlying this remarkable visual stability are still incompletely understood. We used electrocorticography (ECoG) from electrodes directly implanted on the human early visual areas V1, V2, V3d/v, V4d/v and the fusiform gyrus to investigate blink- and saccade-related neuronal suppression effects during non-experimental, free viewing conditions. We found a characteristic, biphasic, broadband gamma power decrease-increase pattern in all investigated visual areas. During saccades, a decrease in gamma power clearly preceded eye movement onset, at least in V1. This may indicate that cortical information processing is actively suppressed in human early visual areas before and during saccades, which then possibly mediates perceptual visual suppression. The following eye movement offset-related increase in gamma power may indicate the recovery of visual perception and the resumption of visual processing.

Measuring the effects of pre-test probability on out-patient first EEG investigation in children – A guide to evidence-based EEG triage in a pandemic

IntroductionThe yield of epileptiform EEG abnormalities is lower in unselected Paediatric populations than in prospective studies of incident seizures or prevalent epilepsy studies. At a time of limited capacity, it is important to match available EEG resources to children who are most likely to benefit. In this study we evaluated a prospective triage tool for estimating the likelihood of epileptiform abnormality in children’s first out-patient EEG. MethodsWe prospectively triaged 1865 out-patient referrals to the largest Paediatric EEG laboratory in Ireland. Based on a structured algorithm, we dichotomized first EEG referrals into priority and non-priority groups and assigned one of 5 sub-levels based on anticipated EEG yield. EEGs were reported by a single Consultant in Clinical Neurophysiology. ResultsTriage designated 757 (41 %) EEG referrals as non-priority. Priority exceeded non-priority referrals for all age groups except children between 18 months and 3.5 years. EEGs showed a two-fold higher incidence of interictal epileptiform abnormalities for priority referrals (36 % vs 18 %, p < 0.001). Rates of interictal epileptiform abnormality correlated with the 5 sub-levels of triage (p < 0.01). Epileptiform yield was highest (39 %) for children over 5 years vs 17 % for those under 5 years (p < 0.00001); these rates increased to 49 % and 20 % respectively for priority referrals. ConclusionStructured pre-test triage of EEG referrals can identify children who have the greatest likelihood of epileptiform abnormality. In a mixed population of Paediatric referrals, the epileptiform yield of first time EEG is 49 % for children over 5 years who are referred with an appropriate EEG indication. This is subject to much variability with epileptiform yields as low as 13 % in younger children with non-priority referrals. The use of a structured triage algorithm can help to optimise utility of EEG in situations of limited laboratory capacity.

Large-Scale Desynchronization During Interictal Epileptic Discharges Recorded With Intracranial EEG.

It is increasingly recognized that deep understanding of epileptic seizures requires both localizing and characterizing the functional network of the region where they are initiated, i. e., the epileptic focus. Previous investigations of the epileptogenic focus' functional connectivity have yielded contrasting results, reporting both pathological increases and decreases during resting periods and seizures. In this study, we shifted paradigm to investigate the time course of connectivity in relation to interictal epileptiform discharges. We recruited 35 epileptic patients undergoing intracranial EEG (iEEG) investigation as part of their presurgical evaluation. For each patient, 50 interictal epileptic discharges (IEDs) were marked and iEEG signals were epoched around those markers. Signals were narrow-band filtered and time resolved phase-locking values were computed to track the dynamics of functional connectivity during IEDs. Results show that IEDs are associated with a transient decrease in global functional connectivity, time-locked to the peak of the discharge and specific to the high range of the gamma frequency band. Disruption of the long-range connectivity between the epileptic focus and other brain areas might be an important process for the generation of epileptic activity. Transient desynchronization could be a potential biomarker of the epileptogenic focus since 1) the functional connectivity involving the focus decreases significantly more than the connectivity outside the focus and 2) patients with good surgical outcome appear to have a significantly more disconnected focus than patients with bad outcomes.

Post-stroke object affordances: An EEG investigation

Rehabilitating upper limb function after stroke is a key therapeutic goal. In healthy brains, objects, especially tools, are said to cause automatic motoric ‘affordances’; affecting our preparation to handle objects. For example, the N2 event-related potential has been shown to correlate with the functional properties of objects in healthy adults during passive viewing. We posited that such an affordance effect might also be observed in chronic-stage stroke survivors. With either dominant or non-dominant hand forward, we presented three kinds of stimuli in stereoscopic depth; grasp objects affording a power-grip, pinch objects affording a thumb and forefinger precision-grip and an empty desk, affording no action. EEG data from 10 stroke survivors and 15 neurologically healthy subjects were analysed for the N1 and N2 ERP components. Both components revealed differences between the two object stimuli categories and the empty desk for both groups, suggesting the presence of affordance-related motor priming from around 100 to 370 ms after stimulus onset. Hence, we speculate that stroke survivors with loss of upper limb function may benefit from object presentation regimes designed to maximise motor priming when attempting movements with manipulable objects. However, further investigation would be necessary with acute stage patients, especially those diagnosed with apraxia.

The Relationship between Carotid Doppler Ultrasound and EEG Metrics in Healthy Preschoolers and Adults.

Despite widespread using electroencephalography (EEG) and Doppler ultrasound in pediatric neurology clinical practice, there are still no well-known correlations between these methods that could contribute to a better understanding of brain processes and development of neurological pathology. This study aims to reveal relationship between EEG and Doppler ultrasound methods. We compared two cohorts of adults and preschool children with no history of neurological or mental diseases. The data analysis included investigation of EEG and carotid blood flow indexes, which are significant in neurological diagnosis, as well as calculation of linear and non-linear EEG parameters and ratios between the systolic peak velocities of carotid arteries and carotid blood asymmetry. We have found age-dependent correlations between EEG and power Doppler ultrasound imaging (PDUI) data. Carotid blood flow asymmetry correlated with delta-rhythm power spectral density only in preschoolers. The ratios of blood flow velocities in the internal carotid arteries to those in the common carotid arteries correlated with higher peak alpha frequency and lower fractal dimension; moreover, they were associated with lower Epworth sleepiness scale scores. The study revealed significant correlations between EEG and PDUI imaging indexes, which are different for healthy children and adults. Despite the fact that the correlations were associated with non-clinical states such as overwork or stress, we assumed that the investigated parameters could be applicable for clinical trials.

Evidence for modulation of EEG microstate sequence by vigilance level

The momentary global functional state of the brain is reflected in its electric field configuration and cluster analytical approaches have consistently shown four configurations, referred to as EEG microstate classes A to D. Changes in microstate parameters are associated with a number of neuropsychiatric disorders, task performance, and mental state establishing their relevance for cognition. However, the common practice to use eye-closed resting state data to assess the temporal dynamics of microstate parameters might induce systematic confounds related to vigilance levels. Here, we studied the dynamics of microstate parameters in two independent data sets and showed that the parameters of microstates are strongly associated with vigilance level assessed both by EEG power analysis and fMRI global signal. We found that the duration and contribution of microstate class C, as well as transition probabilities towards microstate class C were positively associated with vigilance, whereas the sign was reversed for microstate classes A and B. Furthermore, in looking for the origins of the correspondence between microstates and vigilance level, we found Granger-causal effects of vigilance levels on microstate sequence parameters. Collectively, our findings suggest that duration and occurrence of microstates have a different origin and possibly reflect different physiological processes. Finally, our findings indicate the need for taking vigilance levels into consideration in resting-sate EEG investigations.