Relations among EEG-alpha asymmetry,BIS/BAS,and dispositional optimism

Past research has been unable to address whether the activity in the frontal hemispheres is related to the direction of motivation (approach versus withdrawal) or valence of emotion (positive versus negative). The present study was an attempt to address this question by using a standardized low-resolution brain electromagnetic tomography (sLORETA) which provides EEG localization measures that are independent of the recording reference. Resting EEG, self-report measures of Behavioral Activation and Inhibition System (BAS and BIS) strength, dispositional optimism and a measure of hedonic tone, were collected from 51 unselected undergraduates. Three measures of cortical activation were obtained: (a) alpha asymmetry at conventional scalp sites, (b) anterior and posterior source alpha asymmetries (sLORETA method), (c) posterior versus frontal delta and theta activity. Both alpha asymmetry measures (conventional EEG and sLORETA) yielded significant frontal and parietal asymmetry correlation patterns. Neither measure identified significant associations between resting posterior versus frontal delta and theta activity personality traits. Higher BAS was uniquely related to greater left-sided activation in the middle frontal gyrus (BA11). Optimism was associated with higher activations in the left-superior frontal gyrus (BA10) and in the right-posterior cingulate cortex (BA31).     

The influence of mental fatigue on brain activity: Evidence from a systematic review with meta-analyses

The occurrence of mental fatigue during tasks like driving a vehicle increases risk of injury or death. Changes in electroencephalographic (EEG) activity associated with mental fatigue has been frequently studied and considered a promising biomarker of mental fatigue. This is despite differences in methodologies and outcomes in prior research. A systematic review with meta-analyses was conducted to establish the influence of mental fatigue on EEG activity spectral bands, and to determine in which regions fatigue-related EEG spectral changes are likely to occur. A high-yield search strategy identified 21 studies meeting inclusion criteria for investigating the change in EEG spectral activity in non-diseased adults engaged in mentally fatiguing tasks. A medium effect size (using Cohen's g) of 0.68 (95%CI: 0.24–1.13) was found for increase in overall EEG activity following mental fatigue. Further examination of individual EEG spectral bands and regions using network meta-analyses indicated large increases in theta (g = 1.03; 95%CI: 0.79–1.60) and alpha bands (g = 0.85; 95%CI: 0.47–1.43), with small to moderate changes found in delta and beta bands. Central regions of the scalp showed largest change (g = 0.80; 95%CI: 0.46–1.21). Sub-group analyses indicated large increases in theta activity in frontal, central and posterior sites (all g > 1), with moderate changes in alpha activity in central and posterior sites. Findings have implications for fatigue monitoring and countermeasures with support for change in theta activity in frontal, central and posterior sites as a robust biomarker of mental fatigue and change in alpha wave activity considered a second line biomarker to account for individual variability.     

Discriminant Analysis and Equivalent Source Localization of the EEG Related to Cognitive Functions

Discriminant analysis and EEG source localization methods were employed to compare groups of normal subjects during different cognitive conditions using 43-channel EEG recordings in the alpha (8-13 Hz) frequency band. Recordings were obtained from 69 dextral females during 2 passive conditions, Eyes-Open and Eyes-Closed, and 2 active conditions, Word-Finding and Dot-Localization. The cross-spectral matrix between all of the electrode sites was used to characterize the EEGs obtained during each condition. The subjects were partitioned into training and test sets and quadratic discriminant functions were constructed from the training sets to classify the EEGs. The discriminant functions successfully classified both the training and test sets at rates approaching 80%. The classification was repeated using only the diagonal (power spectral) elements of the cross-spectral matrices in the discriminant functions and this approach was successful in discriminating between the EEGs from the passive cognitive conditions but failed to discriminate between the EEGs from the active conditions. Source localization using a modified MUSIC algorithm indicated that the centers of brain electrical activity that distinguished the Eyes-Closed condition from the Eyes-Open condition were located in the medial occipital and right frontal regions. Centers of electrical activity that distinguished the Word-Finding condition from the Dot-Localization condition were located in the right medial posterior and left temporal regions. Validation of the locations of the centers of activity was accomplished by repeating the classification procedures using the spatial patterns generated on the scalp by dipole current sources placed at these locations.     

Progesterone modulates theta oscillations in the frontal-parietal network

The neuroactive metabolites of the steroid hormones progesterone (P4) and testosterone (T) are GABAergic modulators that influence cognition, yet, the specific effect of P4 and T on brain network activity remains poorly understood. Here, we investigated if a fundamental oscillatory network activity pattern, often related to cognitive control, frontal midline theta (FMT) oscillations, are modulated by steroids hormones, P4 and T. We measured the concentration of P4 and T using salivary enzyme immunoassay and FMT oscillations using high-density electroencephalography (EEG) during eyes-open resting-state in 55 healthy women and men. Electrical brain activity was analyzed using Fourier analysis, aperiodic signal fitting, and beamformer source localization. Steroid hormone concentrations and biological sex were used as predictors for scalp and source-estimated amplitude of theta oscillations. Elevated concentrations of P4 predicted increased amplitude of FMT oscillations across both sexes, and no relationship was found with T. The positive correlation with P4 was specific to the frontal midline electrodes and survived correction for the background aperiodic signal of the brain. Using source localization, FMT oscillations were localized to the frontal-parietal network (FPN). Additionally, theta amplitude within the FPN, but not the default mode network, positively correlated with P4 concentration. Our results suggest that P4 concentration modulates brain activity via upregulation of theta oscillations in the FPN.     

Dissociation of frontal‐midline delta‐theta and posterior alpha oscillations: A mobile EEG study

Numerous reports have demonstrated low‐frequency oscillations during navigation using invasive recordings in the hippocampus of both rats and human patients. Given evidence, in some cases, of low‐frequency synchronization between midline cortex and hippocampus, it is also possible that low‐frequency movement‐related oscillations manifest in healthy human neocortex. However, this possibility remains largely unexplored, in part due to the difficulties of coupling free ambulation and effective scalp EEG recordings. In the current study, participants freely ambulated on an omnidirectional treadmill and explored an immersive virtual reality city rendered on a head‐mounted display while undergoing simultaneous wireless scalp EEG recordings. We found that frontal‐midline (FM) delta‐theta (2–7.21 Hz) oscillations increased during movement compared to standing still periods, consistent with a role in navigation. In contrast, posterior alpha (8.32–12.76 Hz) oscillations were suppressed in the presence of visual input, independent of movement. Our findings suggest that FM delta‐theta and posterior alpha oscillations arise at independent frequencies, under complementary behavioral conditions, and, at least for FM delta‐theta oscillations, at independent recordings sites. Together, our findings support a double dissociation between movement‐related FM delta‐theta and resting‐related posterior alpha oscillations. Our study thus provides novel evidence that FM delta‐theta oscillations arise, in part, from real‐world ambulation, and are functionally independent from posterior alpha oscillations.     

Theta and alpha oscillations reflect differences in memory strategy and visual discrimination performance in patients with Parkinson's disease

The aim of the present study was to investigate alterations in brain oscillatory activity during transient intentional encoding of abstract novel shapes in patients with Parkinson's disease (PD). Combined time-frequency analyses of alpha and theta power revealed a clear dissociation between PD patients (N=10) and age-matched healthy controls (N=10). PD patients used sub-optimal stimulus encoding strategies for subsequent maintenance and recall, whereas the controls mainly used categorization processes. In contrast to controls, PD patients showed significantly less theta increase and upper alpha suppression at frontal locations and significant laterality of early posterior theta and lower-2 alpha oscillations at right posterior locations. These findings suggest that the fronto-striatal circuits participate in visual categorization processes. Furthermore, theta and alpha oscillations appear to be involved in mediating the integration processes in mnemonic networks underlying visual categorization.     

Brain oscillation and connectivity during a chemistry visual working memory task

Many studies have reported that frontal theta and posterior alpha activities are associated with working memory tasks. However, fewer studies have focused on examining whether or not the frontal alpha or posterior theta can play a role in the working memory task. This study investigates electroencephalography (EEG) dynamics and connectivity among different brain regions' theta and alpha oscillations. The EEG was collected from undergraduate students (n = 64) while they were performing a Sternberg-like working memory task involving chemistry concepts. The results showed that the frontal midline cluster exhibited sustained theta augmentation across the periods of stimulus presentations, maintenance, and probe presentation, suggesting that the frontal midline theta might associate with facilitating the central execute function to maintain information in the working memory. Study of the central parietal and the occipital clusters revealed a sequence of theta augmentation followed by alpha suppression at constant intervals after the onset of stimulus and probe presentations, suggesting that the posterior theta might be associated with sensory processing, theta gating, or stimulus selection. It further suggests that the posterior alpha event-related de-synchronization (ERD) might be linked to direct information flow into and out of the long-term memory (LTM) and precede stimulus recognition. An alternating phasic alpha event-related synchronization (ERS) and ERD following the 1st stimulus and probe presentations were observed at the occipital cluster, in which alpha ERS might be linked to the inhibition of irrelevant information.     

Aging affects medial but not anterior frontal learning-related theta oscillations

Aging induces a decline in the ties that bind anatomical networks centered on the prefrontal cortex, which are critical for reinforcement learning and decision making. At the neurophysiological level, the prefrontal cortex may engage electrophysiological oscillatory synchronization to coordinate other brain systems during learning. We recorded scalp EEG from 21 older (mean age 69 years) and 20 young (mean age 22 years) healthy human adults while they learned stimulus–response mappings by trial-and-error using feedback. In young adults, theta-band (4–8 Hz) oscillatory power over medial frontal and anterior frontal cortex predicted learning after errors. Older adults demonstrated a decrease in the theta-band learning-predictive signals over medial frontal but not anterior frontal cortex. This age-related decrease in task-relevant medial frontal theta power may be related to the more general decrease in medial frontal theta power that we observed during rest. These results demonstrate a shift in cortical networks that support reinforcement learning in older adults, and shed new light on the changes in neurophysiological (oscillatory) mechanisms with neurocognitive aging.     

P300: The Similarities and Differences in the Scalp Distribution of Visual and Auditory Modality

To examine the topographic relationship of P3(00) between the visual and auditory modalities, especially to examine whether there are any modality-specific hemispheric differences of P3 in normal adults. Methods: The P3s were recorded from the same 41 normal right-handed males between the ages of 20 and 33 in both a typical auditory oddball task and a visual oddball paradigm with novel stimuli, with an extensive set of 61 scalp electrodes. In addition to the visual comparison and quantitative assessment of current source density (CSD) maps between the two modalities, canonical correlation analyses on the P3 raw amplitudes and examination of interaction effects of modality × location on both raw and normalized P3 data were performed. Results: The canonical correlation between modalities was generally high, especially at the left parietal brain region. There were no significant hemispheric effects in anterior brain but significant left-greater- than-right hemispheric effects in posterior brain regions in both modalities; modality-specific hemispheric effect was observed only at the parietal region. Strong surface current density activities were observed in the midline parietal-occipital area, and left and right boundary areas of temporal and inferior frontal region. Conclusions: The topographic similarities between P3s recorded in the visual and auditory modality outnumber the differences. Combining data from CSD assessments and profile analysis of P3 topography support the hypothesis of multiple generators of P3 that are differentially active in processing stimuli from different sensory modalities and are not symmetrically distributed between the two hemispheres.     

Does Greater Low Frequency EEG Activity in Normal Immaturity and in Children with Epilepsy Arise in the Same Neuronal Network?

Greater low frequency power (<8 Hz) in the electroencephalogram (EEG) at rest is normal in the immature developing brain of children when compared to adults. Children with epilepsy also have greater low frequency interictal resting EEG activity. Whether these power elevations reflect brain immaturity due to a developmental lag or the underlying epileptic pathophysiology is unclear. The present study addresses this question by analyzing spectral EEG topographies and sources for normally developing children and children with epilepsy. We first compared the resting EEG of healthy children to that of healthy adults to isolate effects related to normal brain immaturity. Next, we compared the EEG from 10 children with generalized cryptogenic epilepsy to the EEG of 24 healthy children to isolate effects related to epilepsy. Spectral analysis revealed that global low (delta: 1–3 Hz, theta: 4–7 Hz), medium (alpha: 8–12 Hz) and high (beta: 13–25 Hz) frequency EEG activity was greater in children without epilepsy compared to adults, and even further elevated for children with epilepsy. Topographical and tomographic EEG analyses showed that normal immaturity corresponded to greater delta and theta activity at fronto-central scalp and brain regions, respectively. In contrast, the epilepsy-related activity elevations were predominantly in the alpha band at parieto-occipital electrodes and brain regions, respectively. We conclude that lower frequency activity can be a sign of normal brain immaturity or brain pathology depending on the specific topography and frequency of the oscillating neuronal network.     

Information Transfer During a Transitive Reasoning Task

For about two decades now, the localization of the brain regions involved in reasoning processes is being investigated through fMRI studies, and it is known that for a transitive form of reasoning the frontal and parietal regions are most active. In contrast, less is known about the information exchange during the performance of such complex tasks. In this study, the propagation of brain activity during a transitive reasoning task was investigated and compared to the propagation during a simple memory task. We studied EEG transmission patterns obtained for physiological indicators of brain activity and determined whether there are frequency bands specifically related to this type of cognitive operations. The analysis was performed by means of the directed transfer function. The transmission patterns were determined in the theta, alpha and gamma bands. The results show stronger transmissions in theta and alpha bands from frontal to parietal as well as within frontal regions in reasoning trials comparing to memory trials. The increase in theta and alpha transmissions was accompanied by flows in gamma band from right posterior to left posterior and anterior sites. These results are consistent with previous neuroimaging (fMRI) data concerning fronto-parietal regions involvement in reasoning and working memory processes and also provide new evidence for the executive role of frontal theta waves in organizing the cognition.     

大鼠额叶皮质损害后胚脑移植适宜时期的探讨

目的:探讨脑外伤后进行脑组织移植的适宜时期。方法:机械抽吸法制作大鼠右侧额叶皮质损害模型。在大鼠额叶皮质损害后立即、2周及2月时采用铺片法将E15-17天胚脑额叶皮质移植入皮质损害腔内。动物存活2月再进行脑功能测试和形态学观察。结果:额叶皮质损害后立即移植鼠移植侧δ、0频段相对功率值显著高于健侧(P<0.05),α、β频段相对功率值显著低于健侧(P<0.05),脑电功率谱曲线两侧明显不对称,表明受损的脑功能也没有恢复。额叶皮质损害后2周及2月移植鼠移植侧δ、0、α、β频段相对功率值均与健侧近似(P>0.05),脑电功率谱曲线两侧基本对称,脑电功率谱改善。形态学观察可见损害后立即移植鼠少见有移植组织存活,损害后2周及2月移植鼠,绝大多数见有良好的移植组织存活。结论:大鼠额叶皮质损害后2周至2月均为胚脑组织移植适宜时期。     

Hemifield-dependent N1 and event-related theta/delta oscillations: An unbiased comparison of surface Laplacian and common EEG reference choices

Surface Laplacian methodology has been used to reduce the impact of volume conduction and arbitrary choice of EEG recording reference for the analysis of surface potentials. However, the empirical implications of employing these different transformations to the same EEG data remain obscure. This study directly compared the statistical effects of four commonly-used (nose, linked mastoids, average) or recommended (reference electrode standardization technique [REST]) references and their spherical spline current source density (CSD) transformation for a large data set stemming from a well-understood experimental manipulation. ERPs (72 sites) recorded from 130 individuals during a visual half-field paradigm with highly-controlled emotional stimuli were characterized by mid-parietooccipital N1 (125 ms peak latency) and event-related synchronization (ERS) of theta/delta (160 ms), which were most robust over the contralateral hemisphere. All five data transformations were rescaled to the same covariance and submitted to a single temporal or time-frequency PCA (Varimax) to yield simplified estimates of N1 or theta/delta ERS. Unbiased nonparametric permutation tests revealed that these hemifield-dependent asymmetries were by far most focal and prominent for CSD data, despite all transformations showing maximum effects at mid-parietooccipital sites. Employing smaller subsamples (signal-to-noise) or window-based ERP/ERS amplitudes did not affect these comparisons. Furthermore, correlations between N1 and theta/delta ERS at these sites were strongest for CSD and weakest for nose-referenced data. Contrary to the common notion that the spatial high pass filter properties of a surface Laplacian reduce important contributions of neuronal generators to the EEG signal, the present findings demonstrate that instead volume conduction inherent in surface potentials weakens the representation of neuronal activation patterns at scalp that directly reflect regional brain activity.     

The influence of caffeine on human EEG under resting condition and during mental loads

Summary The effect of caffeine (single oral doses of 200 mg and 400 mg) on the CNS was tested under resting conditions and while performing a concentration performance test in a placebo-controlled pilot study on ten healthy males. The EEG was evaluated quantitatively by spectral analysis with a Computer Aided Topographical Electro En-cephalo Metry system. Comparison of the averaged frequency content revealed a clear difference between the change in the functional state of the brain due to the mental arithmetics, on the one hand, and the caffeine effect, on the other. Both states of altered brain activity were reflected in a particular topographical distribution of the frequency change with respect to a frontal-occipital accentuation. Comparison of the two periods of mental arithmetics in the absence or presence of caffeine showed a tendency to concentration-dependent differences from each other. Administration of 200 mg and 400 mg caffeine in the relaxed state effected the decrease in spectral power in the theta and alpha ranges. The concentration performance test without caffeine effected decreases in power in the alpha range in frontal to parietal cortex and enhanced theta power in frontal and occipital regions and the alpha power in occipital cortex. The caffeine-dependent decrease in theta power and the decrease in delta power seen under relaxation conditions after 400 mg are not observed during the concentration performance test in the presence of caffeine.Abbreviation KLT Konzentrationsleistungstest (concentration performance test)     

Diurnal Alterations of Brain Electrical Activity in Healthy Adults: A LORETA Study

EEG background activity was investigated by low resolution brain electromagnetic tomography (LORETA) to test the diurnal alterations of brain electrical activity in healthy adults. Fourteen right-handed healthy male postgraduate medical students were examined four times (8 a.m., 2 p.m., 8 p.m. and next day 2 p.m.). LORETA was computed to localize generators of EEG frequency components. Comparing the EEG activity between 2 p.m. and 8 a.m., increased activity was seen (1) in theta band (6.5–8 Hz) in the left prefrontal, bilateral mesial frontal and anterior cingulate cortex; (2) in alpha2 band (10.5–12 Hz) in the bilateral precuneus and posterior parietal cortex as well as in the right temporo-occipital cortex; (3) in beta1-2-3 band (12.5–30 Hz) in the right hippocampus and parieto-occipital cortex, left frontal and bilateral cingulate cortex. Comparing the brain activity between 8 p.m. and 8 a.m., (1) midline theta activity disappeared; (2) increased alpha2 band activity was seen in the left hemisphere (including the left hippocampus); and (3) increased beta bands activity was found over almost the whole cortex (including both of hippocampi) with the exception of left temporo-occipital region. There were no significant changes between the background activities of 2 p.m. and next day 2 p.m. Characteristic distribution of increased activity of cortex (no change in delta band, and massive changes in the upper frequency bands) may mirror increasing activation of reticular formation and thus evoked thalamocortical feedback mechanisms as a sign of maintenance of arousal.     

Cognitive decline in Parkinson's disease is associated with slowing of resting-state brain activity: a longitudinal study

The pathophysiological mechanisms of Parkinson's disease (PD)-related dementia (PDD) are still poorly understood. Previous studies using electroencephalography (EEG) and magnetoencephalography (MEG) have demonstrated widespread slowing of oscillatory brain activity as a neurophysiological characteristic of PD-related dementia. Here, we use MEG to longitudinally study early changes in oscillatory brain activity in initially nondemented PD patients that may be associated with cognitive decline. Using a longitudinal design, resting-state MEG recordings were performed twice at an approximate 4-year interval in 14 healthy controls and 49 PD patients. Changes in peak frequency and in relative spectral power for 10 brain regions were analyzed in relation to clinical measures of cognitive and motor function. In contrast to healthy controls, PD patients showed a slowing of the dominant peak frequency. Furthermore, analysis per frequency band revealed an increase in theta power over time, along with decreases in alpha1 and alpha2 power. In PD patients, decreasing cognitive performance was associated with increases in delta and theta power, as well as decreases in alpha1, alpha2, and gamma power, whereas increasing motor impairment was associated with a theta power increase only. The present longitudinal study revealed widespread progressive slowing of oscillatory brain activity in initially nondemented PD patients, independent of aging effects. The slowing of oscillatory brain activity strongly correlated with cognitive decline and therefore holds promise as an early marker for the development of dementia in PD.     

The adult self expression scale: Validation by the multitrait-multimethod procedure

The present studies were designed to provide further validation of the Adult Self Expression Scale as a measure of assertive behavior for adults in general. Validation was approached by the Campbell and Fiske multitrait-multimethod procedure and was concerned with the convergent relationship of assertion as measured by the Scale with measures of dominance and abasement as well as the discriminant capability of the instrument in terms of its relationship to various types of aggression, both verbal and physical. A variety of self-report, peer-rating, and unobtrusive measures were obtained from four distinct samples: participants in avocational interest classes at a technical institute, adults enrolled in an evening course in counseling theories at a state university, psychiatric inpatients, and convicted male felons. The results indicated that the Adult Self Expression Scale exhibits moderately strong convergent validity and moderate discriminant validity. The utility of the scale as a measure of assertive behavior for use with adults in general was supported.     

Prestimulus top-down reflection of obsessive-compulsive disorder in EEG frontal theta and occipital alpha oscillations

It has recently been reported that prestimulus electroencephalogram (EEG) frontal theta and occipital alpha oscillations of healthy controls were modulated by the type of upcoming tasks, reflecting prestimulus top-down preparation. The present study explored the differences in dynamics of frontal theta and occipital alpha activities between obsessive-compulsive disorder (OCD) patients and healthy participants in terms of reflection of prestimulus top-down regulation. EEGs were recorded from 16 OCD patients and 16 healthy controls using a color and a shape discrimination task. The power and time course of oscillatory activity were calculated by convolving the EEG signals with Morlet wavelets. Although OCD patients yielded significantly lower total alpha and total theta power results than the normal controls, they demonstrated that significantly higher total alpha and total theta power preceded the difficult task (shape-task) as compared to the easy task (color-task). Furthermore, the frontal region, where OCD patients usually revealed abnormalities, showed significant differences in the prestimulus total theta power between the normal and OCD groups. Taken together, frontal theta and occipital alpha oscillations seem to be potent electrophysiological correlates reflecting impairment in the prestimulus top-down processing of OCD patients.     

Emotional face expressions are differentiated with brain oscillations.

The differentiation of "facial expressions" is a process of higher mental activity, which has considerable applications in "psychology of moods and emotions". We applied the approach of event-related oscillations (EROs) to investigate the modulation of electrical manifestations related to emotional expression in EEG recordings of 20 healthy subjects. EROs of "neutral, angry and happy" faces in 13 electrical recordings sites (F(3), F(4), C(z), C(3), C(4), T(3), T(4), T(5), T(6), P(3), P(4), O(1), O(2)) were analyzed. Following the recording session, the subjects were asked to express the degree of their emotional involvement (valence and arousal) using the Self-Assessment Manikin ratings. Amplitude frequency characteristics (AFCs) were used to determine the frequencies of interest and the ranges for digital pass-band filtering applied accordingly. Consecutively, peak to peak amplitude measures of oscillatory responses were computed for the selected frequency bands and for the differentiation of the different stimuli. A differentiation between angry and happy facial expressions was observed especially in the alpha (9-13 Hz) and beta (15-24 Hz) frequencies, however, only when selecting stimuli with high mood involvement. Therefore, these frequency bands are the main focus of this report. The amplitudes of the alpha responses upon angry face stimulation were significantly higher than upon presentation of the happy faces at posterior locations. At F(3), C(z) and C(3), beta responses upon angry face stimulation were significantly higher in amplitude compared with the happy face stimulation. It is discussed that the frontal theta response is highly increased in comparison to all theta responses also encountered in studies of face recognition: During observation of facial expression, the occipital theta is much higher. We conclude and emphasize that the analysis of brain oscillatory responses distributed over the scalp in combination with subjective ratings of emotional impact of stimuli provide a good basis for analysing the influence of emotional information processing in the brain. In congruence with others, the results support the phylogenetical viewpoint suggesting that angry face stimulations are faster and more ample in responding. Furthermore, frontal, temporal, parietal and occipital lobes seem to be involved in processing of facial expressions, as reflected in an ensemble of different frequency brain oscillatory responses distributed over the scalp.     

Sex differences in EEG coherence during a verbal memory task in normal adults.

Coherence analysis was applied to the EEG of 15 female and 15 male subjects who had to memorise dichotically presented lists of concrete nouns. The EEG was recorded from 16 scalp electrodes placed in accordance with the 10/20 system. The results show significant gender-related differences in total coherence reactivity due to a greater increase of rest to task coherence in female than in male subjects. Women differed by showing higher coherence reactivity in the right hemisphere for all analysed (theta 1, theta 2, alpha 1, and alpha 2) frequency bands. They also had more extensive task-induced increases of interhemispheric coherence in theta bands in comparison with single changes in male subjects. In women these changes were mainly between the frontal electrodes of the left hemisphere paired with posterior electrodes of the other hemisphere. These findings indicate sex-related differences in functional cortical organisation during verbal memory tasks.