EEG Variables Research Articles

AB 83. EEG significance in polysomnography applying continuous positive airway pressure therapy (CPAP) in patients with Obstructive Sleep Apnea Syndrome

Background The goal of this study is to explore the variations of EEG and evaluate the impact of its recording upon the process of discovering the optimal CPAP pressure, aiming at eliminating Obstructive Sleep Apnea episodes.

Behavioural and EEG effects of chronic rapamycin treatment in a mouse model of Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) is a multisystem genetic disorder caused by mutation in either Tsc1 or Tsc2 genes that leads to the hyper activation of the mTOR pathway, a key signalling pathway for synaptic plasticity. TSC is characterized by benign tumors arising in different organs and severe neuropsychiatric symptoms, such as epilepsy, intellectual disability, autism, anxiety and depressive behaviour. Rapamycin is a potent inhibitor of mTOR and its efficacy in treating epilepsy and neurological symptoms remains elusive. In a mouse model in which Tsc1 has been deleted in embryonic telencephalic neural stem cells, we analyzed anxiety- and depression-like behaviour by elevated-plus maze (EPM), open-field test (OFT), forced-swim test (FST) and tail-suspension test (TST), after chronic administration of rapamycin. In addition, spectral analysis of background EEG was performed. Rapamycin-treated mutant mice displayed a reduction in anxiety- and depression-like phenotype, as shown by the EPM/OFT and FST, respectively. These results were inline with EEG power spectra outcomes. The same effects of rapamycin were observed in wild-type mice. Notably, in heterozygous animals we did not observe any EEG and/or behavioural variation after rapamycin treatment. Together these results suggest that both TSC1 deletion and chronic rapamycin treatment might have a role in modulating behaviour and brain activity, and point out to the potential usefulness of background EEG analysis in tracking brain dysfunction in parallel with behavioural testing.

A clinical study of syndromes of idiopathic (genetic) generalized epilepsy

ObjectivesEpidemiologic data concerning idiopathic generalized epilepsies (IGEs) are scarce or often unreliable. In the current study, we specifically analyzed the syndromes of IGE based on their demographic, clinical, and EEG findings to determine if other than the seizure type(s) and age of onset, there are any other distinctive features to distinguish these syndromes of IGEs from one another. Materials and methodsIn this retrospective study, all patients with a clinical diagnosis of IGE were recruited at the outpatient epilepsy clinic at Shiraz University of Medical Sciences, from 2008 to 2011. Demographic variables and relevant clinical and EEG variables were summarized descriptively. Statistical analyses were performed using Chi square and Fisher's exact tests. Results2190 patients with epilepsy were registered at our epilepsy clinic and 442 patients (20.2%) were diagnosed as having IGE. Age of seizure onset was 12±7years. Juvenile myoclonic epilepsy was the most frequent syndrome, followed by epilepsy with generalized tonic–clonic seizures only and juvenile absence epilepsy. Epilepsy risk factors, physical examination, MRI and even EEG could not differentiate various syndromes of IGE. ConclusionThe key element in making the correct diagnosis of an IGE syndrome is obtaining a detailed clinical history. However, other than the seizure type(s) and age of onset, there are no any other distinctive features to distinguish these syndromes of IGEs from one another. Besides, sometimes these syndromes have overlapping features.

Stress regulation and cognitive control: evidence relating cortisol reactivity and neural responses to errors

In this study, we tested the relationship between error-related signals of cognitive control and cortisol reactivity, investigating the hypothesis of common systems for cognitive and emotional self-regulation. Eighty-three participants completed a Stroop task while electroencephalography (EEG) was recorded. Three error-related indices were derived from the EEG: the error-related negativity (ERN), error positivity (Pe), and error-related alpha suppression (ERAS). Pre- and posttask salivary samples were assayed for cortisol, and cortisol change scores were correlated with the EEG variables. Better error-correct differentiation in the ERN predicted less cortisol increase during the task, whereas greater ERAS predicted greater cortisol increase during the task; the Pe was not correlated with cortisol changes. We concluded that an enhanced ERN, part of an adaptive cognitive control system, predicts successful stress regulation. In contrast, an enhanced ERAS response may reflect error-related arousal that is not adaptive. The results support the concept of overlapping systems for cognitive and emotional self-regulation.

Symbol Digit and the Quantitative EEG

The coordination of allocation resource model of brain functioning examines the relations between quantitative EEG (QEEG) variables and cognitive performance on specific tasks. The Digit Symbol (DS) subtest of the Wechsler Adult Intelligence Scales has proven to be a sensitive measure in a variety of clinical conditions. A conceptually and empirically similar task (Symbol Digit [SD]) was employed to examine the QEEG correlates of successful functioning. A sample of 119 participants engaged in a modified SD test for 200 seconds while QEEG data were obtained. The participant verbally provided the matching number to the examiner to avoid any motor component of the task. There were negative relations between performance and magnitudes across almost all locations and across a wide bandwidth (0–64 Hz). Negative relations to SD performance were also observed for increased relative power of beta1, whereas positive relations were found for absolute values of coherences of alpha, beta1 (13–32 Hz), and beta2 (32–64 ...

IS INTERICTAL EEG CORRELATED WITH THE SEIZURE TYPE IN IDIOPATHIC (GENETIC) GENERALIZED EPILEPSIES

Objectiveinvestigated the correlation between different interictal EEG abnormalities observed in patients with idiopathic (genetic) generalized epilepsies (IGEs) and their seizure types. Material & Methods In this cross-sectional study, all patients with the diagnosis of IGE, were recruited in the outpatient epilepsy clinic at Shiraz University of Medical Sciences, Iran, from 2008 through 2010. Demographic variables and relevant clinical and EEG variables were summarized descriptively. Statistical analyses were performed using independent samples T-test, Chi square and Fisher’s Exact tests to determine potentially significant differences. Resultsthirty-six patients were diagnosed ashaving IGE. Interictal EEG findings in patients with generalized tonic-clonic seizure (GTCS) compared to patients without GTCS were not different. Abnormal EEG findings in patients with myoclonic seizures compared to patients without these were not different either. However, normal EEGs were more frequently observed in patients with history of myoclonic seizures (P = 0.0001). EEG findings in patients with absences compared to patients without absences were not different. ConclusionEEG cannot differentiate the seizure types and therefore different syndromes of IGEs. Polyspikes, 3-Hz generalized spike-wave (GSW) complexes and 3.5-6 Hz GSW complexes, alone or in combinations, could be observed in various seizure types and syndromes of IGE. The key element in making the correct diagnosis is a detailed clinical history.

Effects of isoflurane anesthesia with and without dexmedetomidine or remifentanil on quantitative electroencephalographic variables before and after nociceptive stimulation in dogs

To evaluate the influence of various anesthetic protocols and 3 multiples of isoflurane minimum alveolar concentration (MAC) before and after supramaximal stimulation on electroencephalographic (EEG) variables in dogs. 6 healthy adult Beagles (mean ± SD body weight, 16.3 ± 1.0 kg). All dogs underwent 3 anesthesia sessions with a minimum of 1 week separating sessions: isoflurane alone, isoflurane and a constant rate infusion of dexmedetomidine (3 μg/kg/h, IV; ID), and isoflurane and a constant rate infusion of remifentanil (18 μg/kg/h, IV; IR). The MAC of isoflurane was determined via supramaximal electrical stimulation. Quantitative variables (frequency bands and their ratios, median frequency, 95% spectral edge frequency [SEF], and an EEG index) were determined directly before and after supramaximal stimulation at 0.75, 1.0, and 1.5 times the MAC for each session of 20-second epochs. Mean ± SD isoflurane MACs for isoflurane alone, ID, and IR were 1.7 ± 0.3%, 1.0 ± 0.1%, and 1.0 ± 0.1%, respectively. Prestimulation 95% SEF decreased significantly with increasing MAC during the isoflurane alone and ID sessions. Significant decreases in δ frequency band (0.5 to 3.5 Hz) presence and significant increases in β frequency band (> 12.5 Hz) presence, median frequency, and 95% SEF after stimulation were dependent on the MAC and anesthetic protocol. The EEG index had the strongest correlation with increasing MAC during the isoflurane-alone session (ρ = -0.89) and the least in the IR session (ρ = -0.15). Anesthesia with isoflurane alone resulted in the greatest overall EEG depression of all protocols. Use of remifentanil depressed the EEG response to nociceptive stimulation more strongly than did dexmedetomidine. The EEG variables evaluated did not appear useful when used alone as indicators of anesthetic depth in dogs.

Neuropeptide-S Evoked Arousal with Electroencephalogram Slow-Wave Compensatory Drive in Rats

Objectives: Neuropeptide S (NPS) exerts a dual arousal and anxiolytic effect in rodents, which may indicate the potential of a novel class of therapeutic agents in psychiatry. The purpose of this study is to fully describe the nature of electroencephalogram (EEG)-defined waking that mediates these arousal effects. Methods: Effects of the intracerebroventricular infusion of NPS at 2 different doses were characterized over 20 h on sleep-wake architecture and EEG spectral components in rats that were chronically implanted with epidural electrodes for continuous measurement of sleep polygraphic and EEG variables. Results: NPS (1 and 10 nmol) increased active waking (+88 and +87%, respectively), decreased light slow-wave sleep (lSWS) (–84 and –68%, respectively), deep slow-wave sleep (dSWS) (–47 and –33%, respectively) and rapid-eye-movement sleep (–71 and –70%, respectively) during the first 2 h after infusion. The wake-promoting effect of NPS is consistent with a marked lengthening in latency to sleep onset, a decrease in the number of state transitions from wakefulness to lSWS, and a delayed lSWS compensatory response. Interestingly, NPS significantly enhanced waking EEG theta oscillations and slow wave activity during dSWS. Conclusion: The findings suggest that NPS enhanced a consolidated waking associated with a subsequent compensatory EEG slow-wave homeostatic drive rather than rebound sleep duration. The characteristics of NPS-induced waking coupled with enhanced EEG theta oscillations without rebound in sleep are desirable therapeutic features in wake-promoting agents.

High-frequency neuronal network modulations encoded in scalp EEG precede the onset of focal seizures

Modulations of neuronal network interactions by seizure precursors are only partially understood and difficult to measure, in part due to inherent intra- and inter-patient seizure heterogeneities and EEG variability. This study investigated preictal neuromodulations associated with seizures originating in the temporal and/or frontal lobes, using information theoretic parameters estimated from awake scalp EEGs in two frequency ranges, ≤100Hz and >100Hz, respectively. Seizure-related activity at high frequencies has not been extensively estimated in awake scalp EEGs. Based on the statistical similarity of preictal and ictal information parameters, preictal network interactions appeared to be specifically modulated at frequencies >100Hz, but not at lower frequencies. The dynamics of these parameters varied distinctly according to the origin of seizure onset (temporal versus frontal). Although preliminary, and based on a small patient sample for which the potential heterogeneity of multiple anticonvulsive medications was difficult to control, these results suggest that preictal modulations may be estimated from high-frequency scalp EEGs using directional information measures with high specificity to ictal events, and may thus be promising for improving seizure prediction.

Neurophysiological predictors of non-response to rTMS in depression

BackgroundThe application of rTMS in Depression has been very well investigated over the last few years. However, little is known about predictors of non-response associated with rTMS treatment. ObjectiveThis study examined neurophysiological parameters (EEG and ERP) in 90 depressed patients treated with rTMS and psychotherapy and sought to identify predictors of non-response. MethodsThis study is a multi-site open-label study assessing pre-treatment EEG and ERP measures associated with non-response to rTMS treatment. ResultsNon-responders were characterized by 1) Increased fronto-central theta EEG power, 2) a slower anterior individual alpha peak frequency, 3) a larger P300 amplitude, and 4) decreased pre-frontal delta and beta cordance. A discriminant analysis yielded a significant model, and subsequent ROC curve demonstrated an area under the curve of 0.814. ConclusionsSeveral EEG variables demonstrated clear differences between R and NR such as the anterior iAPF, fronto-central Theta and pre-frontal cordance in the Delta and Beta band (representative of increased relative pre-frontal perfusion). The increased P300 amplitude as a predictor for non-response requires further study, since this was the opposite as hypothesized and there were no correlations of this measure with clinical improvement for the whole sample. Combining these biomarkers in a discriminant analysis resulted in a reliable identification of non-responders with low false positive rates. Future studies should prospectively replicate these findings and also further investigate appropriate treatments for the sub-groups of non-responders identified in this study, given that most of these biomarkers have also been found in antidepressant medication studies.

Relationship Between Sleep Spindles and Clinical Recovery in Patients With Traumatic Brain Injury

Few methods can predict the prognosis and outcome of traumatic brain injury. Electroencephalographic (EEG) examinations have prognostic significance in the acute stage of posttraumatic coma, and some EEG variables have been correlated with outcome. Furthermore, spindle activity and reactivity in the acute stage have been associated with good recovery. Assessments of consciousness based on EEG and magnetoencephalographic (MEG) recordings provide valuable information for evaluating residual function, forming differential diagnoses and estimating prognosis. This study objectively investigated how fast spindles could relate to the recovery of consciousness and cognitive function during the post-acute to chronic stages of diffuse axonal injuries (DAIs). Sleep stage 2 was examined in 7 healthy participants and 8 patients with DAIs. Simultaneous EEG and MEG recordings were performed in the post-acute (mean 80 days) and chronic (mean 151 days) stages of recovery. Magnetoencephalography enabled equivalent current dipole estimates of fast spindle sources. Clinical recovery was evaluated by consciousness, neuropsychological examination, and outcome. Six severe and two moderate injuries were studied in patients with favorable 1-year outcomes. In the sub-acute stage, significant decreases were detected in the frequency, amplitude, and cortical activation source strengths of spindle activities, but these recovered during the chronic stage. In the chronic stage, the Wechsler adult intelligence factor scale and subset patterning revealed significant improvement in cognitive function. These results suggested that spindles may reflect recovery of consciousness and cognitive function following a DAI.

Effect of mental fatigue on the central nervous system: an electroencephalography study

BackgroundFatigue can be classified as mental and physical depending on its cause, and each type of fatigue has a multi-factorial nature. We examined the effect of mental fatigue on the central nervous system using electroencephalography (EEG) in eighteen healthy male volunteers.MethodsAfter enrollment, subjects were randomly assigned to two groups in a single-blinded, crossover fashion to perform two types of mental fatigue-inducing experiments. Each experiment consisted of four 30-min fatigue-inducing 0- or 2-back test sessions and two evaluation sessions performed just before and after the fatigue-inducing sessions. During the evaluation session, the participants were assessed using EEG. Eleven electrodes were attached to the head skin, from positions F3, Fz, F4, C3, Cz, C4, P3, Pz, P4, O1, and O2.ResultsIn the 2-back test, the beta power density on the Pz electrode and the alpha power densities on the P3 and O2 electrodes were decreased, and the theta power density on the Cz electrode was increased after the fatigue-inducing mental task sessions. In the 0-back test, no electrodes were altered after the fatigue-inducing sessions.ConclusionsDifferent types of mental fatigue produced different kinds of alterations of the spontaneous EEG variables. Our findings provide new perspectives on the neural mechanisms underlying mental fatigue.

Life or death: prognostic value of a resting EEG with regards to survival in patients in vegetative and minimally conscious States.

ObjectiveTo investigate the potentially prognostic value of a resting state electroencephalogram (EEG) with regards to the clinical outcome from vegetative and minimally conscious states (VS and MCS) in terms of survival six months after a brain injury.MethodsWe quantified a dynamic repertoire of EEG oscillations in resting condition with eyes closed in patients in VS and MCS. The exact composition of EEG oscillations was assessed by analysing the probability-classification of short-term EEG spectral patterns.ResultsResults demonstrated that (a) the diversity and the variability of EEG for Non-Survivors were significantly lower than for Survivors; and (b) a higher probability of mostly delta and slow-theta oscillations occurring either alone or in combination were found during the first assessment for patients with a bad outcome (i.e., those who died) within six months of an injury compared to patients who survived. At the same time, patients with a good outcome (i.e., those who survived) after six months post-injury had a higher probability of mostly fast-theta and alpha oscillations occurring either alone or in combination during the first assessment when compared to patients who died within six months of an injury.ConclusionsResting state EEGs properly analysed may have a potentially prognostic value with regards to the outcome from VS or MCS in terms of survival six months after a brain injury.SignificanceThis work may have implications for clinical care, rehabilitative programmes and medical–legal decisions for patients with impaired consciousness states after being in a coma due to acute brain injuries.

A Meta-Analysis of Electroencephalographic Sleep in Depression: Evidence for Genetic Biomarkers

Research on whether any electroencephalographic (EEG) sleep abnormalities observed among individuals with major depressive disorder (MDD) represent genetic biomarkers remains inconclusive. We aimed to identify EEG-based biomarkers of MDD through a review of studies from three populations: individuals with MDD, individuals with MDD under remission, and never depressed high-risk probands (HRPs) of individuals with MDD. We searched databases such as MEDLINE and PsycINFO for EEG studies published since 1970. Of the 886 records, our selection criteria identified 56 studies that employed standardized EEG scoring procedures and addressed confounds such as participant reactivity and drug effects. We then used fixed-effects models to calculate average weighted mean differences in EEG parameters between clinical groups across these studies. Individuals with MDD differed significantly from control subjects on several EEG variables. However, remitted individuals showed normalization of all affected EEG parameters except rapid eye movement (REM) density and slow-wave sleep (SWS). Surprisingly, proportion of SWS was significantly shorter during remission than depression. Never-depressed HRPs also exhibited significantly elevated REM density and reduced SWS. Finally, these parameters constituted the only two EEG variables that were not moderated by depression severity. Individuals experiencing MDD and those in remission exhibit increased REM density and shortened SWS, as do HRPs with no history of MDD. Thus, this combination of EEG features may represent a genetic biomarker of MDD. Further, SWS appears to be shorter during remission than depression, suggesting its role as both a genetic marker as well as a biological scar of the disorder.

Waking and Sleep Electroencephalogram Variables as Human Sleep Homeostatic Process Biomarkers after Drug Administration

Background/Aims: The correlation between theta activity during wakefulness and slow-wave activity (SWA) during sleep observed after sleep deprivation suggests such patterns can be used as electroencephalogram (EEG) biomarkers of the sleep homeostasis process. Since these EEG components would be very useful objective measures to assess CNS drug effects, we investigated whether the relationship between sleep homeostatic EEG biomarkers could be reproduced after an experimental pharmacological intervention. Methods: Seventeen healthy volunteers took part in a phase I randomized, double-blind, crossover design study. To increase sleep propensity, all participants received a single morning oral dose of olanzapine (5 mg) and placebo. Quantitative EEG analysis was done by power spectra calculations: theta activity (3.5–7.5 Hz) during wakefulness and SWA (0.5–4.0 Hz) during sleep. The relationship between the 2 EEG parameters was assessed by correlating the rise rate (percent/hour) of theta activity in wakefulness and the increase (percent) of SWA in the first non-REM sleep episode. Results: Following olanzapine administration we observed increases in theta activity during wakefulness, and increases in total sleep time, sleep efficiency and slow-wave sleep time during sleep. However, a weak and unreliable correlation was observed between the increases in theta activity and changes in sleep SWA. Conclusions: From these results, we cannot affirm that these waking and sleep EEG variables behave as biomarkers of human sleep homeostasis after drug administration. It is possible that these EEG biomarkers reflect different physiological mechanisms if they are assessed during drug CNS effects.

The Sleep EEG as a Marker of Intellectual Ability in School Age Children

To investigate the within-subject stability in the sleep EEG and the association between the sleep EEG and intellectual abilities in 9- to 12-year-old children. Intellectual ability (WISC-IV, full scale, fluid, and verbal IQ, working memory, speed of processing) were examined and all-night polysomnography was performed (2 nights per subject). Sleep laboratory. Fourteen healthy children (mean age 10.5 ± 1.0 years; 6 girls). Spectral analysis was performed on artifact-free NREM sleep epochs (C3/A2). To determine intra-individual stability and inter-individual variability of the sleep EEG, power spectra were used as feature vectors for the estimation of Euclidean distances, and intraclass correlation coefficients (ICC) were calculated for the 2 nights. Sleep spindle peaks were identified for each individual and individual sigma band power was determined. Trait-like aspects of the sleep EEG were observed for sleep stage variables and spectral power. Within-subject distances were smaller than between-subject distances and ICC values ranged from 0.72 to 0.96. Correlations between spectral power in individual frequency bins and intelligence scores revealed clusters of positive associations in the alpha, sigma, and beta range for full scale IQ, fluid IQ, and working memory. Similar to adults, sigma power correlated with full scale (r = 0.67) and fluid IQ (r = 0.65), but not with verbal IQ. Spindle peak frequency was negatively related to full scale IQ (r = -0.56). The sleep EEG during childhood shows high within-subject stability and may be a marker for intellectual ability.

Electromyographic Activity in the EEG in Alzheimer′s Disease: Noise or Signal?

Many efforts have been directed at negating the influence of electromyographic (EMG) activity on the EEG, especially in elderly demented patients. We wondered whether these “artifacts” might reflect cognitive and behavioural aspects of dementia. In this pilot study, 11 patients with probable Alzheimer's disease (AD), 13 with amnestic mild cognitive impairment (MCI) and 13 controls underwent EEG registration. As EMG measures, we used frontal and temporal 50–70 Hz activity. We found that the EEGs of AD patients displayed more theta activity, less alpha reactivity, and more frontal EMG than controls. Interestingly, increased EMG activity indicated more cognitive impairment and more depressive complaints. EEG variables on the whole distinguished better between groups than EMG variables, but an EMG variable was best for the distinction between MCI and controls. Our results suggest that EMG activity in the EEG could be more than noise; it differs systematically between groups and may reflect different cerebral functions than the EEG.

Increased Intra-Participant Variability in Children with Autistic Spectrum Disorders: Evidence from Single-Trial Analysis of Evoked EEG

Intra-participant variability in clinical conditions such as autistic spectrum disorder (ASD) is an important indicator of pathophysiological processing. The data reported here illustrate that trial-by-trial variability can be reliably measured from EEG, and that intra-participant EEG variability is significantly greater in those with ASD than in neuro-typical matched controls. EEG recorded at the scalp is a linear mixture of activity arising from muscle artifacts and numerous concurrent brain processes. To minimize these additional sources of variability, EEG data were subjected to two different methods of spatial filtering. (i) The data were decomposed using infomax independent component analysis, a method of blind source separation which un-mixes the EEG signal into components with maximally independent time-courses, and (ii) a surface Laplacian transform was performed (current source density interpolation) in order to reduce the effects of volume conduction. Data are presented from 13 high functioning adolescents with ASD without co-morbid ADHD, and 12 neuro-typical age-, IQ-, and gender-matched controls. Comparison of variability between the ASD and neuro-typical groups indicated that intra-participant variability of P1 latency and P1 amplitude was greater in the participants with ASD, and inter-trial α-band phase coherence was lower in the participants with ASD. These data support the suggestion that individuals with ASD are less able to synchronize the activity of stimulus-related cell assemblies than neuro-typical individuals, and provide empirical evidence in support of theories of increased neural noise in ASD.

Effect of body position on bilateral EEG alterations and their relationship with autonomic nervous modulation in normal subjects

This study investigated the effect of body position on the electroencephalogram (EEG) and autonomic nervous modulation, and the relationship between them using spectral analysis of EEG and heart rate variability (HRV). All healthy volunteers recruited had their electrocardiogram and EEG recorded for power spectral analysis. We found that when changing position from supine to upright, the EEG spectral components below the α band, such as δ and θ bands, were significantly decreased while the EEG spectral components above the α band, such as β, γ and ω bands, were significantly increased in both scalps. Correlation analysis showed that the θ rhythm of both scalps might be associated with the control of HR, the α and β rhythms of right scalp might be associated with vagal modulation, and the γ rhythm of left scalp might be associated with sympathetic modulation of the subject. Thus, some EEG components might be associated with the autonomic nervous modulation of the subject during positional change. There might be a mechanism located in the brain-stem which jointly controls both autonomic influences on heart rate and EEG activation.

Comparative EEG mapping studies in Huntington’s disease patients and controls

Huntington's disease (HD) is a devastating neurodegenerative disorder with prominent motor and cognitive decline. Previous studies with small sample sizes and methodological limitations have described abnormal electroencephalograms (EEG) in this cohort. The aim of the present study was to investigate objectively and quantitatively the neurophysiological basis of the disease in HD patients as compared to normal controls, utilizing EEG mapping. In 55 HD patients and 55 healthy controls, a 3-min vigilance-controlled EEG (V-EEG) was recorded during midmorning hours. Evaluation of 36 EEG variables was carried out by spectral analysis and visualized by EEG mapping techniques. To elucidate drug interference, the analysis was performed for the total group, unmedicated patients only and between treated and untreated patients. Statistical overall analysis by the omnibus significance test demonstrated significant (p<0.01 and p<0.05) EEG differences between HD patients and controls. Subsequent univariate analysis revealed a general decrease in total power and absolute alpha and beta power, an increase in delta/theta power, and a slowing of the centroids of delta/theta, beta and total power. The slowing of the EEG in HD reflects a disturbed brain function in the sense of a vigilance decrement, electrophysiologically characterized by inhibited cortical areas (increased delta/theta power) and a lack of normal routine and excitatory activity (decreased alpha and beta power). The results are similar to those found in other dementing disorders. Medication did not affect the overall interpretation of the quantitative EEG analysis, but certain differences might be due to drug interaction, predominantly with antipsychotics. Spearman rank correlations revealed significant correlations between EEG mapping and cognitive and motor impairment in HD patients.