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Two reports in the last issue of this journal attempted to replicate aspects of our previous studies on anterior electroencephalogram (EEG) asymmetry, affective style, and depression. In this commentary, an overview is provided of our model of anterior asymmetries, affective style, and psychopathology. Emphasis is placed on conceptualizing the prefrontal and anterior temporal activation patterns within a circuit that includes cortical and subcortical structures. The causal status of individual differences in asymmetric activation in the production of affective style and psychopathology is considered. Major emphasis is placed on EEG methods, particularly the need for multiple assessments to obtain estimates of asymmetric activation that better reflect an individual's true score. Issues specific to each of the two articles are also considered. Each of the articles has more consistency with our previously published data than the authors themselves suggest. Recommendations are made for future research to resolve some of the outstanding issues.

This study examined the effects of information modalities of cognitive tasks on the EEG laterality. The EEGs were recorded from six scalp areas (P3, P4, W1, W2, O1 and O2) and analyzed the power spectra and intra-hemispheric coherence (P-W, P-O, W-O) for the alpha band. The subjects were 12 male students, and all of them were entirly right-handed. Tasks were two types of the verbal tasks, which were (1) memorizing a set of 9 Chinese words and (2) squaring a double figures, and two types of the spatial tasks, which were (1) imaging and memorizing an unfamiliar picture and (2) imaging a famous picture. The instructions and task stimulus were presented by two types of information modalities. One was visualy displayed on the TV monitor without audio-channel, and the other was presented by the audio monitor without display. Task-related EEG asymmetries were observed in each task and in each modality condition. There were, however, regional differences in the EEG asymmetry among the scalp areas. When the information modality was the audio, the parietal-, Wernicke's area- and even occipital EEG power showed the significant task-related asymmetries. However, when the modality was the video, the significant asymmetry was observed only in the occipital area. These results suggest that the audio-information were processed on more wider hemispheric area than the video-information. Therefore, the audio-tasks may demand more cognitive striving than the visual tasks. There was no effect of cognitive task and information modality on the alpha band coherence. From the analysis of the individual differences, however, it is plausible to think that there is the preference of information modality for the cognitive processing.

The hypothesis was tested that unilateral dopamine deficiency leading to the contralateral extrapyramidal syndrome (hemi-parkinsonism) would cause distinctly asymmetric EEG sleep patterns. In 7 hemi-Parkinson's patients 2 nights of sleep were monitored along with pre-sleep waking periods. No medication was given prior to the first night. The second night followed at least 2 months of l -DOPA medication. Although in all patients sleep architecture was disturbed, no statistically significant asymmetries of sleep patterns were obtained. l -DOPA medication improved the quality of sleep. Delta sleep was most visibly improved. Also, post-treatment enhancement of the mean delta power over the parkinsonian hemisphere was supported statistically. The role of dopamine in slow wave sleep control and mechanism of contralateral hemisphere involvement are discussed.

Bilaterally homologous parietal and temporal EEGs were recorded from two groups of educationally handicapped children while the subjects (Ss) rested with eyes open or closed or performed in simple tasks designed to differentially activate the two hemispheres (reading by Ss, reading to Ss, draw a picture). A 'dyslexic' but not dysphasic group showed a reversal of theta asymmetry from eyes closed to eyes open (L less than R to L greater than R). This difference between groups was reflected most at the parietal placement. Theta in the parietal lead changed in accordance with expectations from reading to drawing (reduction of the R/L ratio), but that pattern did not occur at the temporal lead in 'dyslexics'. A discriminant analysis on theta power correctly classified 20 of the 22 children.

The hypothesis that dreaming is mediated by the right hemisphere was evaluated by monitoring EEG power asymmetry during REM and NREM sleep, and obtaining mentation reports when short-term temporal shifts in the EEG indicated relative left- or right-hemispheric dominance. Content analyses provided no support for the right-hemisphere hypothesis; indeed, some scales showed higher content during relative left-hemispheric dominance. In contrast to earlier reports, no difference between REM and NREM in EEG asymmetry was observed.

Several recent reports concerning the relationship of EEG asymmetry to cognition were evaluated. Technical and interpretive shortcomings of some papers minimizes their significance with respect to this issue, whereas several findings support the notion that EEG asymmetry occurs in association with cognition per se.

EEG from O1 and O2 was recorded from twelve subjects (6 male and 6 female) whilst they carried out a paced inspection task at five separate task speeds. Peak alpha activity was analysed using a spectral analysis technique. The results suggested that when subjects were working at a speed 25% faster than their self-chosen pace they were using predominantly their right hemisphere, whereas then they were working at 25% slower they were using mainly their left hemisphere. It was suggested, based on earlier literature, that subjects may be processing information about the task in different ways at different task paces: A sequential processing strategy is being used at the slow pace whilst a parallel or Gestalt processing strategy is being used at the fast pace.

Nine male artists and eight male engineers were tested for asymmetry of occipital alpha as a function of occupation, lateral speicificity of task, and difficulty of the task. NEbes' ring test and a facial memory test were used as “right hemisphere” tasks, and linguistic and mathematical tasks were chosen as left hemisphere specific. Results found no difference on the basis of occupation or difficulty, and significant results were found for task laterality.

Left-and right-handers have been reported to differ in lateral hemispheric specialization for cognition. We compared different methods of dividing subjects into handedness groups: preference(a 12-item questionnaire), performance(speed, strength, dexterity), and preference plus performance, and determined which method of handedness classification indicated the greatest group differences on EEG and dichotic measures of lateral specialization. All handedness measures were significantly intercorrelated. These handedness measures were significantly correlated with the dichotic test over the whole population but were significantly correlated with EEG asymmetry only in females. Scoring degree of handedness showed significant relationships to lateral specialization which were not seen when subjects were classified into discrete handedness groups. Ambidextrous subjects performed as well as right- or left-handers on unimanual tasks despite a lack of hand preference. The hand used for writing was shown to be too limited to be used as the sole index of handedness in studies related to cognition.

Autoregressive (AR) analysis and component analysis were done on EEGs during sleep stage 2 in normal and autistic children, since AR-coefficients of EEG characterize the autocovariance and power spectral density of EEG. In addition, as the generalized distance of the average AR-coefficient vector of an EEG group at one side from that at the opposite side exhibits an F-distribution, the statistical inferences were determined, as to whether there is hemispheric specialization in EEG in 21 right-handed autistic children and whether there is a difference between the AR-spectral pattern of EEG in the autistic children and that of 28 normal children of the same age range. The results obtained are as follows: 1. Significant hemispheric lateralization in EEG at the significant level of 0.01 was observed in normal children, whereas no lateralization was confirmed in autistic children. 2. Random click stimulation had cumulative effects on the hemispheric lateralization in the normal children, but not in the autistic children. On the contrary, the effects of random flash light stimulation on hemispheric asymmetry were verified in the autistic children as well as in the normal children. 3. The EEG components of autistic children were significantly different from the normal ones in the frequency range of alpha-2 component waves at bilateral frontal (Fp1 and Fp2) regions and the activity of these component waves was higher in the autistic children than in the normal ones over 5 years old. 4. These findings suggest that autistic children are not only less responsive to external stimuli, but also neurophysiologically less active in the internal regulatory mechanism.

Twelve field-dependent and twelve field-independent women, who had previously shown opposite superiorities in a tachistoscopic face recognition task, returned to the laboratory for a session in which EEG asymmetry was measured during two facial and two verbal recognition tasks. Although task-related EEG asymmetries were observed, there was no effect of cognitive style on either direction or amount of asymmetry. These results suggest a lack of comparability among different methods of assessing individual differences in lateral functions.

Encouraging patients to use cognitive reappraisal constitutes the core of modern psychotherapeutic approaches. However, evidence for specific neural correlates of the capacity for cognitive reappraisal, which is a necessary prerequisite for the effective implementation of cognitive reappraisal in everyday life, has been sparse to date. In the present study, the capacity for cognitive reappraisal was studied in terms of the participants' inventiveness in generating alternative appraisals of anger-evoking events, and was correlated with frontal EEG alpha asymmetry recorded while the participants were generating reappraisals as well as during a common creative idea generation task. During cognitive reappraisal efforts, individuals higher on the capacity for generating cognitive reappraisals showed more left-lateralized activity in lateral prefrontal cortex, specifically in ventrolateral prefrontal cortex extending toward the frontal pole. This effect was observed independently from the activation during novel idea generation without emotional component, indicating that specific demands are implicated in the generation of reappraisals of emotional events. Taken together, the results indicate that individuals higher on the capacity for cognitive reappraisal are more capable or more prone to recruit appropriate brain regions when the situation demands coming up with alternative appraisals of stressful events. The findings may stimulate the development of more individually targeted interventions.

This study examined the effects of information modalities of cognitive tasks on the EEG laterality. The EEGs were recorded from six scalp areas (P3, P4, W1, W2, O1 and O2) and analyzed the power spectra and intra-hemispheric coherence (P-W, P-O, W-O) for the alpha band. The subjects were 12 male students, and all of them were entirly right-handed. Tasks were two types of the verbal tasks, which were (1) memorizing a set of 9 Chinese words and (2) squaring a double figures, and two types of the spatial tasks, which were (1) imaging and memorizing an unfamiliar picture and (2) imaging a famous picture. The instructions and task stimulus were presented by two types of information modalities. One was visualy displayed on the TV monitor without audio-channel, and the other was presented by the audio monitor without display. Task-related EEG asymmetries were observed in each task and in each modality condition. There were, however, regional differences in the EEG asymmetry among the scalp areas. When the information modality was the audio, the parietal-, Wernicke's area- and even occipital EEG power showed the significant task-related asymmetries. However, when the modality was the video, the significant asymmetry was observed only in the occipital area. These results suggest that the audio-information were processed on more wider hemispheric area than the video-information. Therefore, the audio-tasks may demand more cognitive striving than the visual tasks. There was no effect of cognitive task and information modality on the alpha band coherence. From the analysis of the individual differences, however, it is plausible to think that there is the preference of information modality for the cognitive processing.

Twenty subjects selected for (overt) task-induced EEG asymmetry performed 17 different covert mental tasks while EEG was recorded from right and left temporoparietal leads. After each task, subjects rated their experiences on four scales: (covert) verbalization, visual imagery, affect, and concentration. Zero-order and semipartial correlations between integrated EEG measures and subjective ratings showed that verbalization and concentration were systematically related to EEG asymmetry. The results suggest that verbal processes may be a more important influence on temporoparietal EEG asymmetry than are visual imagery processes, at least during purely covert tasks. The results also demonstrate that EEG asymmetry reflects lateralized cognitive processes occurring in the absence of external stimuli or overt responses.

EEG lateralization was examined during happy and sad emotional expression in 24 subjects. Happy and sad emotional states were induced by asking subjects to mentally review previously shown film-sequences. Our results failed to replicate those of previous studies, in that they showed no frontal alpha lateralization as a function of emotion. The authors discuss the literature and suggest caution before asserting the existence of electrophysiological arguments in favor of lateralization of emotions in humans.

Lateral asymmetry of electroencephalographic (EEG) spectra was assessed in schizophrenic patients compared to normal controls. Ten predominantly unmedicated schizophrenic inpatients and nine normal controls performed monitored cognitive tasks during bilateral recording of EEG from parietal and temporal sites. Lateralization of EEG power in five frequency bands was compared between the groups; separate analyses were performed for linked ears and vertex references. A subsample of schizophrenic patients was restudied after a period of neuroleptic treatment. All significant group differences were obtained with the linked ears reference only. Pretreatment schizophrenics manifested relatively less alpha power over the right hemisphere during all conditions than controls, particularly in the parietal leads. After treatment, there was a significant shift in alpha lateralization toward the control values. These latter effects were also present in the theta frequency band to a lesser extent.

EEG recordings from 230 carotid endarterectomies performed with an automatic EEG monitoring system were reviewed with the purpose of establishing the exact relation between EEG changes and intraoperative stroke. Patients were selectively shunted, based on the EEG changes occurring after carotid cross-clamping. Transient EEG asymmetry was not associated with intraoperative stroke. Only persisting EEG asymmetry reflected intraoperative major stroke, expressed by a positive predictive value of 0.50, but also in terms of specificity (0.99), sensitivity (0.80) and diagnostic gain (47.8%) of the EEG; minor strokes could not be detected with EEG monitoring. Analysis of the time course of the persisting asymmetry confirmed the thrombo-embolic origin of the majority of the major strokes.

This study was designed to test the hypothesis that Japanese subjects exhibit different patterns of resting EEG asymmetry compared with Westerners. EEG was recorded from the left and right temporal and parietal scalp regions in bilingual Japanese and Western subjects during eyes-open and eyes-closed rest periods before and after the performance of a series of cognitive tasks. Alpha activity was integrated and digitized. Japanese subjects were found to exhibit greater relative right-sided parietal activation during the eyes closed condition. This difference was found to be a function of greater left hemisphere activation among the Westerners. Various possible contributors to this cross-cultural differences are discussed.

The ratio of integrated EEG amplitude from left and right temporal areas was analyzed during sleep in normal subjects for two consecutive nights. The results showed that the differences between the subjects were similar in both nights and were much larger than the differences between the stages of sleep. No significant variation was found between stages, although stage 1 tended to show greater relative right activation in night 1. Also, the relative right activation was greater in wakefulness in night 2 as compared to night 1. The classification of the correlation coefficients between stages corresponded to the physiological transitions between stages, suggesting that the small source of variance due to sleep stage contains relevant information.

This paper reports three studies showing sex differences in EEG asymmetry during self-generated cognitive and affective tasks. In the first experiment, bilateral EEG, quantified for alpha on-line, was recorded from right-handed subjects while they either whistled, sang or recited lyrics of familiar songs. The results revealed significant asymmetry between the whistle and talk conditions only for subjects with no familial left-handedness and, within this group, only for females and not for males. In the second experiment, bilateral EEG was recorded while right-handed subjects (with no familial left-handedness) self-induced covert affective and non-affective states. Results revealed significantly greater relative right-hemisphere activation during emotion versus non-emotion trials only in females; males showed no significant task-dependent shifts in asymmetry between conditions. The third experiment was designed to test the hypothesis that females show greater percent time asymmetry than males during biofeedback training for symmetrical and asymmetrical EEG patterns. Results confirmed this prediction as well as indicating that females show better control of such asymmetrical cortical patterning. These findings provide new neuropsychological support for the hypothesis of greater bilateral flexibility in females during self-generation tasks.

The relationship of EEG asymmetry to spatial performance was studied for high and low spatial ability males and females. As in previous research for high spatial ability males relatively greater right hemispheric activity was associated with successful spatial performance. For low ability males, a group rarely studied, the opposite relationship was found. Both high and low ability females showed no consistent pattern of relationships.

We have studied EEG asymmetry in normal subjects during verbal and spatial tasks. Recordings were made from the left and right temporal and parietal areas, and the ratios of average power (1–35 Hz) in homologous leads T4/T3 and P4/P3 were computed. This ratio (right over left) was greater in the verbal tasks than in the spatial tasks. With this measure we have been able to distinguish between these two cognitive modes as they occur in normal subjects, using simple scalp recording.

Event-related potentials (ERPs) and other electroencephalographic (EEG) evidence show that frontal brain areas of higher and lower socioeconomic status (SES) children are recruited differently during selective attention tasks. We assessed whether multiple variables related to self-regulation (perceived mental effort) emotional states (e.g., anxiety, stress, etc.) and motivational states (e.g., boredom, engagement, etc.) may co-occur or interact with frontal attentional processing probed in two matched-samples of fourteen lower-SES and higher-SES adolescents. ERP and EEG activation were measured during a task probing selective attention to sequences of tones. Pre- and post-task salivary cortisol and self-reported emotional states were also measured. At similar behavioural performance level, the higher-SES group showed a greater ERP differentiation between attended (relevant) and unattended (irrelevant) tones than the lower-SES group. EEG power analysis revealed a cross-over interaction, specifically, lower-SES adolescents showed significantly higher theta power when ignoring rather than attending to tones, whereas, higher-SES adolescents showed the opposite pattern. Significant theta asymmetry differences were also found at midfrontal electrodes indicating left hypo-activity in lower-SES adolescents. The attended vs. unattended difference in right midfrontal theta increased with individual SES rank, and (independently from SES) with lower cortisol task reactivity and higher boredom. Results suggest lower-SES children used additional compensatory resources to monitor/control response inhibition to distracters, perceiving also more mental effort, as compared to higher-SES counterparts. Nevertheless, stress, boredom and other task-related perceived states were unrelated to SES. Ruling out presumed confounds, this study confirms the midfrontal mechanisms responsible for the SES effects on selective attention reported previously and here reflect genuine cognitive differences.