Intrahemispheric EEG Coherence Research Articles

EEG coherence before and after giving birth

During pregnancy and the postpartum period, changes in brain volume and in motivational, sensory, cognitive, and emotional processes have been described. However, to date, longitudinal modifications of brain function have been understudied. To explore regional cortical coupling, in pregnancy and at 3 months postpartum, we analyzed resting-state electroencephalographic (EEG) coherence in the delta, theta, alpha1, alpha2, beta1, and beta2 frequency bands across frontal and parietal regions of the maternal brain (Fp1, Fp2, F3, F4, P3, and P4). We found that from pregnancy to the postpartum period, mothers showed less intrahemispheric EEG coherence between the frontal and parietal regions in the alpha1 and alpha2 bands, as well as greater interhemispheric EEG coherence between frontopolar regions in the beta2 band. These changes suggest decreased inhibition of neural circuits. These neurophysiological changes may represent an adaptive process characteristic of motherhood.

Inter- and Intra-Hemispheric EEG Coherence Study in Adults with Neuropsychiatric Disorders.

Functional connectivity between different regions of the brain in the resting state has been a recent topic of interest in neurophysiological research. EEG coherence happened to be an useful tool for measuring changes in neuro-psycho-physiological functioning which are not detectable by simply measuring amplitude or power spectra. The aim of our study was to investigate the changes in the EEG coherence in groups of different mental disorders such as: depression, general anxiety disorder, ADHD, Asperger syndrome and headaches, compared to control group. All measures were made in two conditions: eye opened (EO) and eyes closed (EC). The obtained results show that in EO condition there is a significantly lower coherence for delta waves between analyzed groups. For theta coherence only for Asperger syndrome we found lower coherence compared to control group, ADHD and headaches in parietal region (P3-P4). Obtained results for intrahemispheric coherence have shown that there was significantly lower coherence in both conditions for delta and theta bands in almost all sites for Asperger's syndrome, and opposite increased intrahemispheric coherence for patients with headaches (for delta band in the anterior regions and for theta band in the posterior regions). ADHD patients expressed lower delta inter-hemispheric coherence in frontal regions, and increased coherence of theta in central regions but increased delta coherence in posterior regions only in EO condition. For depressive and anxiety patients we found decreased intrahemispheric coherence for EO condition for delta brain waves all over the cortex. Concerning the coherence in anxiety patients in our current study we have obtained hypo coherence in centro-parieto-occipital region only for delta in inter-hemispheric coherence and also lower delta coherence through the cortex for intrahemispheric coherence. Our findings for interhemispheric hyper coherence in subjects with depression specifically for alpha and beta bands were confirmed in other studies. We suggest that EEG coherence analysis could be a sensitive parameter in the detection of electrophysiological abnormalities in patients with anxiety, depression, ADHD, Asperger syndrome and headaches. These results can confirm the development of QEEG state and trait biomarkers for psychiatric disorders.

Inter- and Intrahemispheric EEG Coherence and Visuomotor Performance During Shooting Competition and Practice.

This study compared inter- and intrahemispheric cortical networking and visuomotor performance during practice and competition in 14 air pistol athletes (mean age of 17.8 years). Participants self-reported their competitiveness, stress, confidence, and relaxation through visual analog scales; shooting score and aiming time were measured by the SCATT program. Inter- and intrahemispheric coherences during aiming were analyzed. Under competition following the practice condition, self-reported competitiveness and stress were higher, but confidence was lower. Aiming time during competition was longer than during practice; but there were no significant shooting score differences between conditions, perhaps due to only low-grade competitive anxiety. Through coherence analysis, interhemispheric coherence during aiming was higher under competition, relative to practice. Competitive anxiety seems to result in reduced neural efficiency and regional cortical autonomy, though there was no intrahemispheric electroencephalogram coherence difference between competition and practice conditions.

Transcranial Direct Current Stimulation Modulates Cortical Neuronal Activity in Alzheimer's Disease.

Quantitative electroencephalography (qEEG) showed that Alzheimer's disease (AD) is characterized by increased theta power, decreased alpha and beta power, and decreased coherence in the alpha and theta band in posterior regions. These abnormalities are thought to be associated with functional disconnections among cortical areas, death of cortical neurons, axonal pathology, and cholinergic deficits. Since transcranial Direct Current Stimulation (tDCS) over the temporo-parietal area is thought to have beneficial effects in patients with AD, in this study we aimed to investigate whether tDCS benefits are related to tDCS-induced changes in cortical activity, as represented by qEEG. A weak anodal current (1.5 mA, 15 min) was delivered bilaterally over the temporal-parietal lobe to seven subjects with probable AD (Mini-Mental State Examination, MMSE score >20). EEG (21 electrodes, 10–20 international system) was recorded for 5 min with eyes closed before (baseline, t0) and 30 min after anodal and cathodal tDCS ended (t1). At the same time points, patients performed a Word Recognition Task (WRT) to assess working memory functions. The spectral power and the inter- and intra-hemispheric EEG coherence in different frequency bands (e.g., low frequencies, including delta and theta; high frequencies, including alpha and beta) were calculated for each subject at t0 and t1. tDCS-induced changes in EEG neurophysiological markers were correlated with the performance of patients at the WRT. At baseline, qEEG features in AD patients confirmed that the decreased high frequency power was correlated with lower MMSE. After anodal tDCS, we observed an increase in the high-frequency power in the temporo-parietal area and an increase in the temporo-parieto-occipital coherence that correlated with the improvement at the WRT. In addition, cathodal tDCS produced a non-specific effect of decreased theta power all over the scalp that was not correlated with the clinical observation at the WRT. Our findings disclosed that tDCS induces significant modulations in the cortical EEG activity in AD patients. The abnormal pattern of EEG activity observed in AD during memory processing is partially reversed by applying anodal tDCS, suggesting that anodal tDCS benefits in AD patients during working memory tasks are supported by the modulation of cortical activity.

Wake EEG coherence before and after sleep in adults with autism: decreased morning frontal connectivity

Autism is a neurodevelopemental disorder characterized by atypical connectivity between brain regions. People with autism are known to have sleep disorders and the purpose of this study was to analyze brain connectivity before and after a night of sleep using EEG coherence analysis. Nine adults with autism (21.1 ± 4.0 years) and 20 control participants (20.8 ± 4.2 years) were recorded for two consecutive nights in a sleep laboratory, using a 22-electrode montage. Every participant had a normal IQ and none were taking medication. Wake EEG was recorded for 5 min at bedtime and just before final rise time in the morning, while lying in bed with eyes closed. EEG coherence values were compared with a multivariate repeated measures design using Group × Moment × Frequency band factors for each electrode separately, followed by post hoc tests. In the evening, the autistic group displayed more Alpha coherence than controls within the left visual area (P3-O1: p = 0.049; T5-O1: p = 0.03 and T5-P3: p = 0.014). In the morning more Alpha coherence in the autistic group within the left visual area was also measured (T5-O1: p = 0.009 and T5-P3: p = 0.015) as well as more Delta coherence at the T5-O1 electrode pair ( p = .027). Moreover, morning recordings showed less Delta coherence within the right frontal area, (Fp2-F8: p = 0.037; F4-F8: p = 0.011) and between left and right hemispheres (F3-F4: p = 0.019; F7-F8: p = 0.003). A previous study performed during REM sleep (Léveillé et al., 2010) found a greater intrahemispheric EEG coherence in autistic participants compared to controls between the left visual cortex and regions either close to or distant from it. The present results are in the same direction, upon both evening and morning wake recordings, suggesting that sleep per se is not responsible for these signs of overconnectivity. The present results also revealed a morning specific lower EEG coherence values for slow frequencies in the right frontal area in participants with autism compared to controls, suggesting that sleep per se could be responsible for these signs of underconnectivity. Canadian Institute for Health Research; ”Fonds de recherche du Québec – Santé”.

Increasing Hippocampal Atrophy and Cerebrovascular Damage Is Differently Associated With Functional Cortical Coupling in MCI Patients

The aim of this study was to assess the changes of intrahemispheric and interhemispheric linear spectral electroencephalography (EEG) coherence associated with increasing hippocampal atrophy (HA) and white matter hyperintensities (WMHs) in patients with mild cognitive impairment (MCI). Eighty-five MCI patients underwent clinical and neuropsychologic assessment, EEG recordings, and magnetic resonance imaging. Intrahemispheric (fronto-temporal, temporo-parietal, and fronto-parietal) and interhemispheric (frontal, temporal, and parietal) linear EEG coherence was computed. MCI patients were categorized into classes of increasing HA and WMHs on the basis of tertile distribution of volume loss (high, mid, and low). Neuropsychologic tests were also gathered and compared in MCI subgroups. As expected, MCI patients with high WMHs had poorer performance on visuospatial and cognitive flexibility, whereas those with high HA failed on memory tests. Significant differences of EEG functional coupling were present in the fronto-temporal network in patients with high WMHs and high HA, but without a different pattern. In high WMHs the EEG coherence in low frequencies was increased (with the exception of alpha1 band), whereas coherence in the fast frequencies was decreased proportional to increasing damage. In high HA a change of coherence was present in the delta and alpha2 frequency bands that was not proportional to HA, fast frequencies being unaffected. Our results show a lateralization (right hemisphere for cerebrovascular disease and left hemisphere for hippocampal atrophy) of the pathologic modifications of functional coupling.

Cerebrovascular Disease and Hippocampal Atrophy Are Differently Linked to Functional Coupling of Brain Areas: An EEG Coherence Study in MCI Subjects

The working hypothesis of paper is that the functional coupling of brain areas is combined with different neuroradiological substrates and has different clinical manifestations. 31 normal old subjects and 85 subjects with mild cognitive impairment (MCI) underwent EEG recordings and magnetic resonance imaging (MRI). Intrahemispheric and interhemispheric linear EEG coherences were computed. At first, all normal old and MCI subjects were compared. Subsequently, three subgroups of MCI were obtained based on neuroradiological substrate (subcortical cerebrovascular damage, MCI-CVD; cholinergic pathways vascular damage MCI-CHOL; and hippocampal atrophy, MCI-HIPP) and compared with a normal old sample matched for age, education and Mini-Mental State Examination score. The group of MCI subjects compared to normal old subjects shows: 1) decrease of intrahemispheric coherence in fronto-parietal regions (both right and left hemisphere); 2) increase of interhemispheric coherence on frontal regions in delta frequency; and 3) increase of interhemispheric coherence on temporal regions (from delta to alpha3 frequency bands). In the MCI subgroups, hippocampal atrophy is linked to an increase of interhemispheric coherence seen on frontal and temporal regions whereas subcortical CVD is linked to the largest decrease of coherence in fronto-parietal regions. MCI-CVD patients performed worst on Trail Making Test battery whereas MCI-HIPP patients were impaired on Rey word list delayed recall and Rey figure recall.

State-dependent changes in intrahemispheric EEG coherence for patients with acute exacerbation of schizophrenia

Abnormalities of electroencephalographic (EEG) coherence in schizophrenia are thought to reflect functional disconnections between different brain regions associated with the onset of this disease. To clarify whether these abnormalities change in a symptom-dependent manner in individual patients, we analyzed the coherence of resting EEGs recorded at two time points with a 36.6-day interval during the course of treatment for 14 patients who had been hospitalized for acute exacerbation of schizophrenia. Symptom severity was quantitatively measured by means of the Brief Psychiatric Rating Scale (BPRS). Beta (13–20 Hz) coherence for the left frontal (F7)–temporal (T5) electrode pair was less than that for the corresponding right pair (F8–T6) at the initial test. At the second test, when symptoms had improved, the left frontal–temporal beta coherence had increased, resulting in disappearance of the laterality. This change in beta coherence for the left frontal–temporal pair correlated negatively with the change in the total BPRS score, particularly the positive symptom score. Similar correlations were found for eight patients who had been drug-free at the first examination. These results suggest that a functional disconnection between the frontal and the temporal lobe in the left hemisphere may be associated with the generation of acute psychotic symptoms in schizophrenia.

Inter-and intra-hemispheric EEG coherence in patients with mild cognitive impairment at rest and during working memory task

To assess functional relationship by calculating inter- and intra-hemispheric electroencephalography (EEG) coherence at rest and during a working memory task of patients with mild cognitive impairment (MCI). The sample consisted of 69 subjects: 35 patients (n=17 males, n=18 females; 52-71 years old) and 34 normal controls (n=17 males, n=17 females; 51~63 years old). Mini-mental state examination (MMSE) of two groups revealed that the scores of MCI patients did not differ significantly from those of normal controls (P>0.05). In EEG recording, subjects were performed at rest and during working memory task. EEG signals from F3-F4, C3-C4, P3-P4, T5-T6 and O1-O2 electrode pairs are resulted from the inter-hemispheric action, and EEG signals from F3-C3, F4-C4, C3-P3, C4-P4, P3-O1, P4-O2, T5-C3, T6-C4, T5-P3 and T6-P4 electrode pairs are resulted from the intra-hemispheric action for delta (1.0-3.5 Hz), theta (4.0-7.5 Hz), alpha-1 (8.0-10.0 Hz), alpha-2 (10.5-13.0 Hz), beta-1 (13.5-18.0 Hz) and beta-2 (18.5-30.0 Hz) frequency bands. The influence of inter- and intra-hemispheric coherence on EEG activity with eyes closed was examined using fast Fourier transformation from the 16 sampled channels. During working memory tasks, the inter- and intra-hemispheric EEG coherences in all bands were significantly higher in the MCI group in comparison with those in the control group (P<0.05). However, there was no significant difference in inter- and intra-hemispheric EEG coherences between two groups at rest. Experimental results comprise evidence that MCI patients have higher degree of functional connectivity between hemispheres and in hemispheres during working condition. It suggests that MCI may be associated with compensatory processes during working memory tasks between hemispheres and in hemispheres. Moreover, failure of normal cortical connections may exist in MCI patients.

Age and gender effects in EEG coherence: III. Girls with attention-deficit/hyperactivity disorder

Objective This study investigated intrahemispheric and interhemispheric EEG coherences as a function of age in girls with different DSM-IV subtypes of Attention-Deficit/Hyperactivity Disorder (AD/HD). It completes a series of 3 studies aimed at clarifying developmental and gender impacts on the coupling between brain regions in this disorder. Methods Three groups of 40 children (AD/HD combined type, AD/HD inattentive type, and normal controls) participated. Each group contained 8 females in each of 5, 1-year age bands from 8 to 12 years. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intrahemispheric electrode pairs (4 in each hemisphere), and 8 interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. Results Developmental effects in intrahemispheric coherences at shorter and longer inter-electrode distances were not as predicted by Thatcher's two-compartment model, contrary to previous findings in boys. Females with AD/HD showed evidence of developmental delay and widespread anomalous elevations in coherence. Girls with AD/HD of the combined type showed similar but greater anomalies than girls with AD/HD of the inattentive type. Conclusions Girls with AD/HD show coherence anomalies relative to age- and gender-matched controls, which differ substantially from those shown by boys with AD/HD. These coherence anomalies did not differ in nature between girls with different DSM-IV subtypes of AD/HD, suggesting that subtype differences in girls reflect only symptom severity. Significance The data reported here indicate qualitative differences in EEG coherences in girls with AD/HD compared with controls, and quantitative differences between girls with different subtypes of AD/HD. Both sets of effects differ in nature from those previously found in boys with AD/HD, showing the need to carefully consider gender in future studies of AD/HD.

Effects of methylphenidate on EEG coherence in Attention-Deficit/Hyperactivity Disorder

This study investigated the effects of methylphenidate on intrahemispheric and interhemispheric EEG coherence in children with Attention-Deficit/Hyperactivity Disorder (AD/HD). Twenty boys with AD/HD Combined type and 20 age- and sex-matched control subjects, aged 8 to 13 years, participated in this study. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for eight intrahemispheric electrode pairs (four in each hemisphere), and eight interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. AD/HD children were tested both off and, 6 months later, on a therapeutic dose of methylphenidate. In intrahemispheric comparisons, AD/HD children had lower theta coherences at long inter-electrode distances, and reduced lateralisation at both long and short–medium inter-electrode distances than controls. For interhemispheric comparisons, AD/HD children showed increased coherences in the frontal regions for the low frequency bands (delta and theta), and reduced coherences in the alpha bands in all other regions. These EEG coherences suggest reduced cortical differentiation and specialisation in AD/HD, particularly in the frontal regions. Methylphenidate did not produce any changes in coherence values. The lack of sensitivity of coherence measures to methylphenidate in the present study suggests that eyes-closed resting EEG coherence measures are associated with structural connectivity of the underlying regions of the brain rather than the degree of functionality of these regions. These results suggest the existence of structural as well as functional brain dysfunction in AD/HD.

Abnormal cortical functional connections in Alzheimer’s disease: analysis of inter- and intra-hemispheric EEG coherence

To investigate inter- and intra-hemispheric electroencephalography (EEG) coherence at rest and during photic stimulation of patients with Alzheimer's disease (AD). Thirty-five patients (12 males, 23 females; 52 to approximately 64 y) and 33 sex- and age-matched controls (12 males, 21 females; 56 to approximately 65 y) were recruited in the present study. EEG signals from C3-C4, P3-P4, T5-T6 and O1-O2 electrode pairs resulted from the inter-hemispheric action, and EEG signals from C3-P3, C4-P4, P3-O1, P4-O2, C3-O1, C4-O2, T5-O1 and T6-O2 electrode pairs resulted from the intra-hemispheric action. The influence of inter- and intra-hemispheric coherence on EEG activity with eyes closed was examined, using fast Fourier transformation from the 16 sampled channels. The frequencies of photic stimulation were fixed at 5, 10 and 15 Hz, respectively. The general decrease of AD patients in inter- and intra-hemispheric EEG coherence was more significant than that of the normal controls at the resting EEG, with most striking decrease observed in the alpha-1 (8.0-9.0 Hz) and alpha-2 (9.5-12.5 Hz) bands. During photic stimulation, inter- and intra-hemispheric EEG coherences of the AD patients having lower values in the alpha (9.5-10.5 Hz) band than those of the control group. It suggests that under stimulated and non-stimulated conditions, AD patients had impaired inter- and intra-hemispheric functional connections, indicating failure of brain activation in alpha-related frequency.

Age and gender effects in EEG coherence: II. Boys with attention deficit/hyperactivity disorder

Objective This study investigated intra-hemispheric and inter-hemispheric EEG coherences as a function of age in boys with different subtypes of Attention Deficit/Hyperactivity Disorder (AD/HD), in comparison with a control group of normal boys. Methods Three groups of 40 children (AD/HD combined type, AD/HD inattentive type, and normal controls) participated. Each group contained 8 males in each 1 year band from 8 to 12 years. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intra-hemispheric electrode pairs (4 in each hemisphere), and 8 inter-hemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. Results Developmental effects in intra-hemispheric coherences at shorter and longer inter-electrode distances generally supported Thatcher's two-compartment model. Control boys showed evidence of development in longer-range inter-hemispheric coherences which was not apparent in AD/HD boys. Boys with AD/HD of the combined type showed qualitatively different anomalies than boys with AD/HD of the inattentive type. Conclusions EEG coherences in normal boys of this age range develop systematically with age in a non-linear fashion. Boys with AD/HD do not show this development. They display coherence anomalies which differ in nature between DSM-IV subtypes, suggesting differences which are not relatable to simple symptom severity. Significance The data reported here indicate differences in the development of EEG coherences in boys with AD/HD, and point to differences between the AD/HD subtypes which may help understanding of the disorder.

Age and gender effects in EEG coherence: I. Developmental trends in normal children

Objective: This study investigated intra-hemispheric and inter-hemispheric EEG coherences as a function of age and gender in normal children. Methods: Two groups of 40 boys and 40 girls, each containing 8 normal children in each 1-year band from 8 to 12 years, participated. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intra-hemispheric electrode pairs (4 in each hemisphere), and 8 inter-hemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. Results: There was consistent evidence of coherences developing across this age range, particularly in long-range intra- and inter-hemispheric electrode pairs. Coherences were larger in the left hemisphere than the right. Coherences also appeared to develop further in males than females, across several regions and frequency bands, suggesting that females lag males in this aspect of brain development. Conclusions: EEG coherences in normal children of this age range develop systematically with age. These developmental effects vary substantially with gender, brain region and frequency bands. Significance: The data reported here provide basic norms for coherence development in different brain regions in normal children.

The size of corpus callosum and functional connectivities of cortical regions in finger and shoulder movements

The correlations between the size of corpus callosum and the inter- and intra-hemispheric EEG coherence and the spatial EEG synchronization during finger and shoulder movements were analyzed in nine right-handed men. The cross-sectional surface areas of corpus callosum (CC) and of seven callosal regions were measured from the mid-sagittal slice of the anatomical MRI. Movement-related coherence between pairs of EEG electrodes overlying the central and parietal regions of both hemispheres was computed after spatially filtering EEG data by the Laplacian operator method. The spatial EEG synchronization was evaluated using Ω-complexity, a novel measure which quantifies the number of independent sources of spontaneous EEG oscillations. The amplitude of coherence between the left and right S1/M1 areas after movement onset in the lower alpha band (7.8–9.8 Hz) correlated with the size of the callosal body in both types of movement. The size of the callosal body also correlated with the C3–Cz coherence in the 15.6–19.5 Hz band in finger movement, and in the 15.6–23.5 Hz band in shoulder movements. The size of the rostral, anterior intermediate and posterior intermediate truncus of CC correlated with Ω-complexity in both types of movements indicating more foci of synchronized EEG oscillations in subjects with a large callosal truncus. The results suggest that the size of callosal truncus which is known to connect the primary sensorimotor and the supplementary motor areas of both hemispheres contributes to the coupling of EEG oscillations during voluntary finger and shoulder movements.

Longitudinal genetic analysis of EEG coherence in young twins.

During middle childhood, continuous changes occur in electroencephalogram (EEG) coherence, an index of cortico-cortical connectivity of the brain. In the gradual development of EEG coher ence, occasional "growth spurts" are observed which coincide with periods of discontinuous development in cognition. Discontinuous development may reflect changes in the genetic architecture of a trait over time, for instance, by the emergence of new genetic factors. To examine stability and change in genetic and environmental influences on EEG coherence from ages 5 to 7 years, intrahemispheric EEG coherences from 14 connections were collected twice in 209 twin pairs. Overall, heritabilities (h2) were moderate to high for all EEG coherences at both ages (average: 58%). For occipito-cortical connections in the right hemisphere, h2 increased with age due to a decrease in environmental variance. For prefronto-cortical connections in the left hemisphere, h2 decreased with age due to a decrease in genetic variance. New genetic factors at age 7 were found for prefronto-parietal coherence, and centro-occipital and parieto-occipital EEG coherences in both hemispheres and, in the left hemisphere, for prefronto-frontal EEG coherences. Mean genetic correlation for these cortico-cortical connections over time was 0.72, indicating that at least part of the genetic influences is age-specific. We argue that this is convincing evidence for the existence of stage-wise brain maturation from years 5 to 7, and that growth spurts in EEG coherence may be part of the biological basis for discontinuous cognitive development at that age range.

The role of cerebral regulatory structures in the formation of human EEG

This article generalizes the results of many years’ studies of the EEG of patients with tumorous lesions in the diencephalic, brainstem, and limbic structures, which fulfill the regulatory function in ensuring integral brain activity. The specific features of the inclusion of individual structures under investigation in the organization of the intra- and interhemispheric relations of cortical biopotentials were demonstrated against the background of diffuse changes in the biopotentials that reflect the systemic character of neurodynamic reorganizations when the regulatory brain structures are involved in the pathological process. This study expands the idea of the predominant functional connection of the diencephalic structures with the right hemisphere and brainstem structures with the left one with determination of the regional specific features of changes in the intrahemispheric EEG coherences. The distinguishing features of intercentral relations when the limbic structures are involved in the pathological process show similarity with the neurodynamic reorganizations in patients with lesions in both diencephalic and (even more so) brainstem structures. Universal elements were detected in the formation of integral adaptive reactions of the brain with lesions in its regulatory structures, which reflects their close functional interaction and makes it possible to consider them the individual links of an integral regulatory system. The study revealed reciprocal changes in various forms of electrical activity, which reflects reciprocation of interaction of individual regulatory structures. This is one of the EEG equivalents of the formation of adaptive-compensatory cerebral reactions. The specificity of influence of the studied regulatory structures are clearly seen in situations of their morphofunctional isolation observed during cerebral coma. In these conditions, when the cortex is functionally inactive, the authors demonstrated the dynamic character of changes in interhemispheric asymmetry, which reflects the dominance of individual links of the regulatory system playing the role of supreme regulator of life support of the body in critical states.

Aberrant Functional Organization in Schizophrenia: Analysis of EEG Coherence during Rest and Photic Stimulation in Drug-Naive Patients

EEG coherence provides a measure of functional correlations between two EEG signals. The present study was conducted to examine intrahemispheric EEG coherence at rest and during photic stimulation (PS) in 18 drug-naive patients with paranoid schizophrenia and 30 control subjects. Compared with the controls, the schizophrenic patients had significantly higher intrahemispheric coherence of the resting EEG for the delta band, although no significant group differences were found for other frequency bands. EEG analysis during PS showed that the patients also had significantly higher EEG coherence over the left posterior regions. In this study, we also examined the changes in intrahemispheric coherence from rest to the stimulus condition (i.e., PS-related coherence reactivity); the patients were found to show significantly smaller changes, with significant group differences being also confined to the posterior regions in the left hemisphere. These findings provide evidence that schizophrenic patients have abnormal EEG coherence in both resting and stimulus conditions and suggest more diffuse, undifferentiated functional organization within hemispheres. In addition, diminished coherence reactivity suggests a failure of PS-related functional reorganization in schizophrenia.

Aging, smoking and EEG coherence: a preliminary study.

Although the cigarette smoking habit is prevalent in young, middle aged and elderly adults, it is yet unknown whether a long term smoking history alters the aging brain and/or whether the aging brain demonstrates an altered sensitivity to acute smoking. Inter- and intrahemispheric EEG coherence was compared in 20 young (18-39 years) adults (10 smokers, 10 nonsmokers) and 20 elderly (64-81 years) adults (10 smokers, 10 nonsmokers). The acute effects of sham inhaling on a nonlighted cigarette and cigarette smoking on EEG coherence was also compared in young and elderly adult smokers. In general, elderly adults exhibited reduced interhemispheric coherence values relative to young adults and, depending on the frequency band, age effects varied with recording site. Smokers of both age groups exhibited greater interhemispheric total alpha coherence values than nonsmokers. Similar smoker status effects were found with fast alpha but this varied with recording site. Relative to sham smoking, acute cigarette smoking reduced interhemispheric slow alpha in both young and elderly smokers but reduced total alpha coherence only in elderly smokers. The results are discussed in relation to normal and pathological aging, including dementia.

Inter- and intrahemispheric EEG coherence during light drowsiness.

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.