Attention tasks and EEG power spectra.

The authors attempted to observe differences in alpha and beta hemispheric asymmetry during a task in which attention was directed toward input from the environment (intake task) as opposed to tasks that required that environmental events be excluded from the focus of attention (rejection tasks). In comparison to resting, both attention tasks caused a shift in alpha asymmetry ratios toward increased power on the right, with the greatest effect at temporal leads. The only significant difference between attention tasks was a finding of higher alpha power during intake than during rejection. Some characteristics of the EEG during attention indicate potential clinical utility.     

Effects of feedback control on EEG alpha asymmetry during covert mental tasks

EEG alpha (8-12 Hz) was recorded bilaterally from O1-P3 and O2-P4 during two eyes-closed sessions in 40 women. During one session subjects performed two covert right-hemisphere activation tasks and two covert left-hemisphere activation tasks (no-biofeedback condition). During the other session subjects performed the same tasks while trying to control their EEG asymmetries, being provided with EEG asymmetry auditory feedback (biofeedback condition). The ratios of integrated EEG alpha amplitudes were calculated as measure of hemispheric asymmetry, and the number of times that the right and left alpha had the same phase angle was determined as index of hemispheric synchrony (alpha phase index). In both conditions, subjects rated orally after each task their degree of subjective fullfilment of the task. There were significant differences between the EEG asymmetry during right- and left-hemisphere tasks. Significant differences of integrated alpha amplitudes and ratios between the no-biofeedback and biofeedback condition were also found. There was more hemispheric asymmetry in the biofeedback than in the no-biofeedback condition, and a significantly higher alpha phase index. There was no correlation between fullfilment ratings and alpha ratios in the no-biofeedback condition, but there was such correlation during right and left hemisphere tasks in the biofeedback condition. The study demonstrated that biofeedback regulation and covert mental activity can have effects on EEG alpha asymmetry which are cumulative.     

EEG network connectivity changes in mild cognitive impairment — Preliminary results

Resting state EEGs were compared between patients with amnestic subtype of mild cognitive impairment (aMCI) and matched elderly controls at two times over a one year period. The study aimed at investigating the role of functional connectivity between and within different brain regions in relation to the progression of cognitive deficit in MCI. The EEG was recorded in two sessions during eyes closed and eyes open resting conditions. Functional brain connectivity was investigated based on the measurement of phase synchronization in different frequency bands. Delta and theta synchronization characteristics indicated decreased level of local and large-scale connectivity in the patients within the frontal, between the frontal and temporal, and frontal and parietal brain areas which was more pronounced 1 year later. As a consequence of opening the eyes connectivity in the alpha1 band within the parietal lobe decreased compared to the eyes closed condition but only in the control group. The lack of alpha1 band reactivity following eye opening could reliably differentiate patients from controls. Our preliminary results support the notion that the functional disconnection between distant brain areas is a characteristic feature of MCI, and may prove to be predictive in terms of the progression of this condition.     

Resting EEG in first-episode and chronic schizophrenia

We examined the frequency characteristics of the electroencephalogram (EEG) in 102 schizophrenic patients (44 first-episode and 58 chronic patients) and 102 normal comparison subjects. EEGs of schizophrenic patients had more delta (1–3 Hz) and theta (3.125–8 Hz) activity and less alpha (8.125–13 Hz) activity than normal comparison subjects. There were no significant differences in the EEG frequency composition of first-episode and chronic patients. Because first-episode and chronic patients were characterized by different disorder durations and treatment histories, the similarity of their EEGs suggests that EEG abnormalities are stable characteristics of schizophrenia and are not treatment-related epiphenomena. A principal components analysis of EEG power bands identified an augmented low frequency-diminished alpha component and a beta component. Schizophrenic patients had significantly higher scores on the augmented low frequency-diminished alpha component than did normal comparison subjects, and there was no significant group difference in scores on the beta component. The findings of this investigation suggest that EEG abnormalities in schizophrenia reflect aspects of brain dysfunction.     

Tackling creativity at its roots: evidence for different patterns of EEG alpha activity related to convergent and divergent modes of task processing

The distinction between convergent and divergent cognitive processes given by Guilford (1956) had a strong influence on the empirical research on creative thinking. Neuroscientific studies typically find higher event-related synchronization in the EEG alpha rhythm for individuals engaged in creative ideation tasks compared to intelligence-related tasks. This study examined, whether these neurophysiological effects can also be found when both cognitive processing modes (convergent vs. divergent) are assessed by means of the same task employing a simple variation of instruction. A sample of 55 participants performed the alternate uses task as well as a more basic word association task while EEG was recorded. On a trial-by-trial basis, participants were either instructed to find a most common solution (convergent condition) or a most uncommon solution (divergent condition). The answers given in the divergent condition were in both tasks significantly more original than those in the convergent condition. Moreover, divergent processing was found to involve higher task-related EEG alpha power than convergent processing in both the alternate uses task and the word association task. EEG alpha synchronization can hence explicitly be associated with divergent cognitive processing rather than with general task characteristics of creative ideation tasks. Further results point to a differential involvement of frontal and parietal cortical areas by individuals of lower versus higher trait creativity.     

Hemispheric Specificity: A Physiological Concomitant of Hypnotizability

MacLeod-Morgan (1979) found a significant relationship between hypnotizability and EEG hemispheric specificity. Hemispheric specificity is defined as the extent to which the alpha ratio between hemispheres changes during lateralized task performance. The present study was designed to replicate and extend this finding. EEG was recorded bilaterally from 44 subjects during performance of two right- and two left-hemisphere discontinuous tasks from MacLeod-Morgan (1979), and four new comparable continuous tasks. As predicted, significant differences were found in hemispheric specificity between low and high hypnotizables especially during the continuous tasks.     

EEG activity during cognitive processing: influence of attentional factors

The research draws upon two separate areas of inquiry: that of lateralized electrocorical processing of cognitive material; and that of psychophysiological information processing studies related to foci of attentional demands. Eighteen subjects on each of three separate days were presented with tasks considered to be 'right hemispheric' or 'left hemispheric'. These tasks were paired in a 2 X 2 design with an attentional factor requiring attention to the environment or to internal processing. All subjects received all types of tasks. Bilateral EEG measures were taken from the frontal and parietal areas referenced to linked ears. Major frequency bands were determined by a Fast Fourier Transform (FFT) and appropriate ANOVAs performed. The results suggest that task factors (left vs right hemisphere tasks) and attentional demands (internal vs external) are differentially represented in terms of EEG functioning. In general the higher beta frequencies were more sensitive to the hemispheric tasks demands and the middle frequencies (alpha and low beta) more sensitive to the attentional demands especially in the parietal areas.     

Thalamocortical theta coherence in neurological patients at rest and during a working memory task.

We simultaneously recorded the local field potential (LFP) in the thalamus and the electroencephalogram (EEG) on the scalp of 5 patients suffering from neurogenic pain, epilepsy and movement disorders. In an earlier study [], we have investigated the slowing of EEG and the high thalamocortical coherence in the framework of thalamocortical dysrhythmia, the common underlying pathophysiology. The current study focuses on the effects of different cognitive conditions. When patients rested with eyes closed, a theta peak dominated the EEG spectra. The peak height was reduced upon opening the eyes, reminiscent of the classical alpha blocking. This peak reduction also appeared in the thalamic LFP recording. When patients activated their working memory by counting backwards, the theta peak increased in scalp EEG or in the LFP recorded in thalamic nuclei VA/VL. The coherence estimates between EEG and LFP ranged between 21% and 76% for different patients and cognitive conditions (mean: 50%). The involvement of both cortex and thalamus in working memory and the high thalamocortical coherence underline, in addition to cortico-cortical interactions, the importance of thalamocortical modules in the generation of higher cognitive functions.     

Lateral Specialization of Cognitive Mode: II. EEG Frequency Analysis

This study reports a frequency analysis of hemispheric EEG asymmetries in normal subjects performing cognitive tasks. Language and arithmetic tasks were expected to engage primarily the left hemisphere; spatial and musical tasks were expected to engage primarily the right hemisphere. Both motor and non-motor tasks were used, e.g. writing a letter and composing a letter mentally. Recordings from temporal leads (T₃,T₄) and parietal leads (P₃,P₄) referred to the vertex C_z were subjected to discrete Fourier transforms; ratios of power from homologous leads (T₄/T₃, P₄/P₃) were computed in conventional frequency bands. These ratios (right/left) are significantly higher in verbal and arithmetic tasks than in spatial tasks primarily in the alpha band; the beta and theta bands show this effect less consistently. The delta band shows no such systematic effect of cognitive mode. Considering the alpha band alone reveals a task dependence of the asymmetry 2–5 times greater than we reported earlier for whole band power (1–35 Hz). Whenever a significant task dependence of asymmetry appears in any band, it is in the same direction: the hemisphere primarily engaged in the cognitive activity develops proportionately less power. The requirement of motor output increases the task dependence of alpha asymmetry and lowers alpha power levels.     

Left Hemisphere Specialization for Facial and Manual Imitation

The hypothesis that the left cerebral hemisphere is specialized for the production of facial and manual motor imitation was tested. The measure of hemispheric specialization was electroencephalographic (EEG) recordings of alpha rhythm (8–12 Hz) asymmetries from homologous parietal sites taken during spatial, verbal, and motor imitation tasks. It was found that both language and motor imitation tasks were significantly more left-lateralized than spatial tasks. The language and imitation tasks did not differ significantly in terms of the pattern of hemispheric specialization exhibited. Based on these findings, it was concluded that the left hemisphere is more directly involved in the production of facial and manual gestures. The role of motor imitation in the development of left hemisphere specialization for language is discussed.     

Comparative neurobiological and neuropsychological deficits in adolescent and adult schizophrenic and nonschizophrenic patients

A group of 24 adolescents and young adults were classified according to four measures using Research Diagnostic Criteria on the dimension of the severity of their schizophrenic syndrome. Independent assessments by the Gottschalk-Gleser Social Alienation-Personal Disorganization Scale and the Abrams-Taylor Emotional Blunting Scale corroborated that the definite schizophrenic group (n = 7) was significantly more schizophrenic than the not schizophrenic group (n = 12), but not more so than the probably schizophrenic group (n = 5). The Halstead-Reitan Category Test and Rhythm Test significantly differentiated the definite schizophrenic group from the not schizophrenic group with respect to cognitive impairment. The Gottschalk-Gleser Cognitive Impairment Scale did not indicate a significant difference in cognitive function between these patient groups. The computerized EEG revealed a significantly higher percent of EEG abnormalities among the definite and probably schizophrenic groups than the not schizophrenic group of patients. These findings are analyzed and discussed.     

认知负载状态下的精神分裂症患者脑电图特异性研究

认知功能损害是精神分裂症的三大原发症状之一,在疾病早期发现和高危人群风险预警等方面具有重要价值。为了研究精神分裂症患者在认知负载状态下的脑电图特异性,本试验收集17例精神分裂症患者和19例健康受试者的脑电信号作为对照,基于小波变换提取各频段信号,计算非线性动力学及脑功能网络属性等特征,并利用机器学习算法将两类人群进行自动分类分析。试验结果表明,两组受试者在认知负载状态下,Fp1和Fp2导联在α、β、θ、γ这4个频带的关联维数和样本熵的差异均具有统计学意义,提示大脑额叶功能损伤是精神分裂症认知功能损害的重要原因。进一步基于机器学习的自动分类分析结果表明,将非线性动力学与脑功能网络属性相结合作为分类器的输入特征,所得分类效果最优,其结果显示准确率为76.77%、敏感度为72.09%、特异性为80.36%。本研究结果表明,脑电信号的非线性动力学和脑功能网络属性等特征,或可作为精神分裂症早期筛查和辅助诊断的潜在生物标记物。     

The dimensional complexity of the EEG during cognitive tasks reflects the impaired information processing in schizophrenic patients.

The aim of the present study was to investigate whether schizophrenic patients show a different change of the dimensional complexity of the EEG, as represented by the Grassberger-Procaccia correlation dimension D(2,) under cognitive challenge compared to normal control subjects. With respect to results reported in the literature, it was expected that the complexity of the signal under cognitive challenge is higher in schizophrenic patients than in normal control subjects reflecting the impaired information processing abilities of the patients. Eighty-seven schizophrenic and 30 matched control subjects performed two different types of the continuous performance task. The results revealed differences between schizophrenic patients and control subjects for the performance as well as the complexity measures. Schizophrenic patients produced more omission errors than normal subjects did. For the EEG complexity measure no differences occurred under the baseline condition. In contrast, during the first minute under task conditions the control subjects showed a decrease of the dimension while no changes were found for the schizophrenic group. These results occurred for both types of the cognitive task but they reached clear significance only in one of them. The results are interpreted as reflecting the ability of normal subjects to adapt their information processing system to the cognitive challenge and to focus their attention on the task while schizophrenic subjects do not show this adaptation to the task.     

Reactive gaze laterality in schizophrenic patients

Reflective lateral eye movements (LEMs) in response to questions of different categories are indicative of differential hemispheric reactivity. These LEMs were studied in schizophrenic patients and normal subjects, in response to 24 questions (12 visual-emotional and 12 verbal-neutral). Two categories of saccades were observed: short-latency LEMs (S-LEMs) and long-latency LEMs (L-LEMs). S-LEMs are believed to be associated with orienting response mechanism. L-LEMs are considered to be related to decision-making or formulating hemispheric-activity-dependent response strategy. In the present study, a general trend of leftward LEMs was found among normals regardless of the question's category, whereas schizophrenics tended to show predominantly rightward LEMs. This suggests that individual cognitive style, rather than task variables, affects LEM direction. The two types of LEM's and their different involvement in hemispheric activity are discussed.     

EEG correlates of emotional tasks related to attentional demands

This research brings together two separate areas: (1) that of EEG processes associated with positive and negatively valenced emotional material; and (2) that of traditional psychophysiological research related to the “intake” and “rejection” of environmental stimuli. Forty males on each of two days were presented with tasks reflecting both attentional demands and affectual processing. Heart rate and bilateral EEG measures from frontal, parietal and temporal sites were recorded. Using a FFT (fast Fourier transform) electrocortical activity in the 2–7 Hz, 8–15 Hz, and 16–24 Hz was determined and analyzed. The results suggest emotional valence (i.e. positive and negative) and attentional demands (i.e. intake vs rejection) are differentially represented in terms of EEG functioning. An interaction of attentional demand with hemisphere was found for EEG alpha activity in the temporal and parietal areas. For emotional valence there was a significant main effect for EEG beta activity in both the temporal and parietal areas. Differential hemispheric activity was found using a factor analytic technique (PARAFAC) with positively valenced tasks being associated with right temporal beta. Heart rate changes for the attentional dimension were consistent with previous research.     

Repeated acoustic stimulation of acute schizophrenic patients and the habituation of EEG power changes

Habituation in psychiatric patients to repeated stimuli has typically been described in connection with the measurement of the skin conductance orienting response. Here EEG power spectra of acute schizophrenic patients and normals to 4 trials of an acoustic stimulation were examined for evidence of habituation. In response to stimulation the alpha EEG reactivity was less distinct in schizophrenics than in normals. This is in agreement with the theory of hypovariability or hyperstability of the EEG in schizophrenics. Signs of habituation in acute schizophrenics were clearer in fast beta frequencies of the parietal leads.     

Effects of stimulus-independent oculomotor activity on the occipital EEG

In order to assess the effects of oculomotor activity on the occipital alpha rhythm, 24 subjects performed each of 2 instructed tasks — random eye movement and eye movement suppression — under conditions of darkness (with eyes both open and closed) and illumination (eyes open in a Ganzfeld). Recordings of the occipital EEG indicated a general blocking of alpha during periods of oculomotor activity for 2 dependent measures, percent time alpha and mean duration of alpha bursts, by comparison with baseline intervals of relaxation. These results are interpreted as support for the activating effects of efferent, oculomotor processes on the alpha component of the EEG.     

Electroencephalographic and brain stem evoked responses from learning‐disabled and control children

This study examined both electroencephalography (EEG) and brain stem evoked responses (BSERs) as indices of cortical dysfunction in children who experience learning disabilities (LD). Fifteen 9‐ to 12‐year‐olds from self‐contained LD classrooms were compared with 15 control children of the same age‐range for eyes‐open and eyes‐closed spontaneous EEG and for lateral symmetry of click‐elicited BSERs. Spontaneous EEG with eyes closed showed the largest between‐group differences over the bilateral temporal sites, where the LD group demonstrated a relative depression of delta and theta frequency bands and a relative increase in alpha. Control children, however, exhibited a more orderly progression or rate of maturation in EEG development compared to LD children. Neither differences in latencies of BSER peaks, I, III, and V, nor lateral asymmetry in BSERs were found between the diagnostic groups. Similar to the findings for EEGs, control children exhibited a more systematic increase in BSER peak latencies as a function of age. The lack of developmental changes for the LD group with the electrophysiological indices may be associated with atypical brain electrical activity and subsequent performance on cognitive‐related tasks.     

EEG alpha power and alpha power asymmetry in sleep and wakefulness.

Asymmetry of waking electroencephalography (EEG) alpha power in frontal regions has been correlated with waking emotional reactivity and the emotional content of dream reports. Little is known regarding alpha asymmetry during sleep. The present study was performed to compare alpha power and alpha power asymmetry in various brain regions across states of sleep and wakefulness. Waking and sleep EEG were recorded in a group of patients undergoing polysomnographic evaluation for possible sleep disorders. Alpha EEG asymmetry in frontal and temporal regions was significantly correlated in waking versus sleep, particularly during rapid eye movement (REM) sleep. These results suggest that patterns of frontal alpha asymmetry are stable across sleep and waking and may be related to emotional reactivity during dreaming. During sleep, alpha power was highest during slow-wave sleep and lowest during REM sleep. Implications of these data for understanding the functional significance of alpha power during waking and sleeping are considered.     

Individual differences in alpha rhythm responsivity: Inter-task consistency and relationships to cardiovascular and dispositional variables

Individual differences in EEG alpha rhythm responsivity were examined with respect to: (1) consistency of response across cognitive tasks; (2) relationships to cardiovascular responsivity; and (3) relationships to dispositional variables. Inter-task correlations revealed a significant degree of stability in subjects' alpha responses to four ‘sensory rejection’ tasks: mental arithmetic, time estimation and imagining oneself as cold or warm. Individuals evidencing greater suppression of alpha activity during mental arithmetic also displayed greater heart rate increase and greater digital vasoconstriction, as well as obtaining higher scores on the Activity subscale of the EASI-III Temperament Survey and on the ‘Hard Striving’ subscale of the Jenkins Activity Survey for Health Prediction, a measure of the Coronary-Prone Behavior Pattern. Alpha responsivity in the time estimation and warm imagery tasks was also associated with greater heart rate increase. The results suggest that alpha responsivity is related to individual differences affecting one's attentiveness or involvement in experimental tasks.