Lateral specialization of cognitive mode: II. EEG frequency analysis

EEG alpha and theta time-frequency structure during a written mathematical task

Since the first electroencephalogram (EEG) was obtained, there have been many possibilities to use it as a tool to access brain cognitive dynamics. Mathematical (Math) problem solving is one of the most important cortical processes, but it is still far from being well understood. EEG is an inexpensive and simple indirect measure of brain operation, but only recently has low-cost equipment (mobile EEG) allowed sophisticated analyses in non-clinical settings. The main purpose of this work is to study EEG activation during a Math task in a realistic environment, using mobile EEG. A matching pursuit (MP)-based signal analysis technique was employed, since MP properties render it a priori suitable to study induced EEG activity over long time sequences, when it is not tightly locked to a given stimulus. The study sample comprised sixty healthy volunteers. Unlike the majority of previous studies, subjects were studied in a sitting position with their eyes open. They completed a written Math task outside the EEG lab, wearing a mobile EEG device (EPOC+). Theta [4 Hz-7.5 Hz], alpha (7.5 Hz-13 Hz] and 0.5 Hz micro-bands in the [0.5 Hz-20 Hz] range were studied with a low-density stochastic MP dictionary. Over 1-min windows, ongoing EEG alpha and theta activity was decomposed into numerous MP atoms with median duration around 3 s, similar to the duration of induced, time-locked activity obtained with event-related (des)synchronization (ERS/ERD) studies. Relative to Rest, there was lower right-side and posterior MP alpha atom/min during Math, whereas MP theta atom/min was significantly higher on anteriorly located electrodes, especially on the left side. MP alpha findings were particularly significant on a narrow range around 10 Hz-10.5 Hz, consistent with FFT alpha peak findings from ERS/ERD studies. With a streamlined protocol, these results replicate previous findings of EEG alpha and theta activation obtained during Math tasks with different signal analysis techniques and in different time frames. The efficient application to real-world, noisy EEG data with a low-resolution stochastic MP dictionary shows that this technique is very encouraging. These results provide support for studies of mathematical cognition with mobile EEG and matching pursuit.

Hypnotizability-Related Asymmetries: A Review

Hypnotizability is a dispositional trait reflecting the individual ability to modify perception, memory and behavior according to imaginative suggestions. It is measured by validated scales that classify the general population in high (highs), medium (mediums) and low (lows) hypnotizable persons, predicts the individual proneness to respond to suggestions, and is particularly popular in the field of the cognitive control of pain and anxiety. Different hypnotizability levels, however, have been associated with specific brain morpho-functional characteristics and with peculiarities in the cognitive, sensorimotor and cardiovascular domains also in the ordinary state of consciousness and in the absence of specific suggestions. The present scoping review was undertaken to summarize the asymmetries observed in the phenomenology and physiological correlates of hypnosis and hypnotizability as possible indices of related hemispheric prevalence. It presents the findings of 137 papers published between 1974 and 2019. In summary, in the ordinary state of consciousness, behavioral, neurophysiological and neuroimaging investigations have revealed hypnotizability related asymmetries mainly consisting of pre-eminent left hemisphere information processing/activation in highs, and no asymmetries or opposite directions of them in lows. The described asymmetries are discussed in relation to the current theories of hypnotizability and hypnosis.

Detecting cognitive hacking in visual inspection with physiological measurements

Cyber threats are targeting vulnerabilities of human workers performing tasks in manufacturing processes, including visual inspection to bias their decision-making, thereby sabotaging product quality. This article examines the use of priming as a form of "cognitive hacking" to adversely affect quality inspection decisions in manufacturing, and investigates physiological measurements as means to detect such intrusion. In a within-subject design experiment, twenty participants inspected surface roughness of a manufactured component with and without exposure to priming on the display of an inspection logging system. The results show that the presence of primes impacted accuracy on surface roughness, cortical activities at parietal lobe P4, and eye gaze for inspecting components. The experiment provides supporting evidence that basic hacking of a worker display can be an effective method to alter decision making in inspection. The findings also illustrate that cortical activities and eye gaze can be useful indicators of cognitive hacking. A major implication of the study results is that physiological indicators can be effective at revealing unconscious cognitive influence in visual inspection.

Statistical modeling for visualization evaluation through data fusion

There is a high demand of data visualization providing insights to users in various applications. However, a consistent, online visualization evaluation method to quantify mental workload or user preference is lacking, which leads to an inefficient visualization and user interface design process. Recently, the advancement of interactive and sensing technologies makes the electroencephalogram (EEG) signals, eye movements as well as visualization logs available in user-centered evaluation. This paper proposes a data fusion model and the application procedure for quantitative and online visualization evaluation. 15 participants joined the study based on three different visualization designs. The results provide a regularized regression model which can accurately predict the user's evaluation of task complexity, and indicate the significance of all three types of sensing data sets for visualization evaluation. This model can be widely applied to data visualization evaluation, and other user-centered designs evaluation and data analysis in human factors and ergonomics.

The Influence of Motor Processes on Attitudes Toward Novel Versus Familiar Semantic Stimuli

Recent research has suggested that the motor processes elicited by upper arm isometric flexion and extension can subtly influence attitudes. Specifically, ideographs evaluatively categorized while performing isometric upper arm flexion were subsequently preferred to ideographs evaluatively categorized while performing isometric upper arm extension. The present research sought to replicate this attitudinal effect with semantic stimuli and to examine a theoretical boundary condition posited by the elaboration likelihood model (ELM). Subjects categorized either neutral words or pronounceable nonwords while adopting the isometric positions. Results indicated that motor processes influenced subsequent attitudes toward stimuli with few associations (i.e., nonwords) more than toward stimuli with many associations in memory (i.e., familiar words). These results are consistent with a growing literature on the possible influence of nondeclarative (e.g., procedural) knowledge on attitudes.

The M100 component of evoked magnetic fields differs by scaling factors: implications for signal averaging

MEG and EEG studies of event-related responses often involve comparisons of grand averages, requiring homogeneity of the variances. Here, we examine the possibility, implied by the nature of neural sources and the measuring principles involved, that the M100 component of auditory-evoked magnetic fields of different subjects, hemispheres, to different stimuli, and at different sensors differs by scaling factors. Such a multiplicative model predicts a linear increase in the standard deviation with the mean, and thus would have important implications for averaging and comparing such data. Our analyses, at the sensor and the source level, clearly show that the multiplicative model applies. We therefore propose geometric, rather than arithmetic, averaging of the M100 component across subjects and suggest a novel and superior normalization procedure. Our results question the justification of the common practice of subtracting arithmetic grand averages.

Disabilities of arithmetic and mathematical reasoning: perspectives from neurology and neuropsychology

Current research on brain-behavior relationships in disabilities of arithmetic and mathematical reasoning is reviewed from both a neurological and a neuropsychological perspective. Although no entirely satisfactory statement of the relationship between arithmetic skills and brain functions has yet emerged, investigators in this area have provided evidence regarding the involvement of some brain systems in processes of calculation. Also, the developmental importance of right- versus left-hemisphere integrity for the mediation of arithmetic learning and performance has been suggested. We propose that an account of brain-behavior relationships in children intended to explain and predict developmental disabilities of arithmetic learning needs to address several important content and processing distinctions in order to (a) encompass empirically derived subtypes of children with learning disabilities who exhibit difficulties with arithmetic and (b) provide adequate direction for future subtyping and intervention research.

Intention as a component of the alpha-rhythm response to mental activity

Many studies of alpha-rhythm reactivity conclude that alpha is selectively attenuated by attention accompanying mental activity. The topography of this attenuation is assumed to match the relevant functional topography of the cortex. But there are reports of apparent increased attention resulting in no change, or even enhanced alpha - the paradoxical response. It is proposed that in this case, alpha amplitude may be dependent on an intention component of behaviour. Some conflicting reports of alpha reactivity to mental processes may then be resolved. It is argued that the classical attention model of alpha is untenable, except for simple sensori-motor responses. Reasons are given to support this and the concept of intention as a neuropsychological variable is introduced. Evidence is presented for a generalisation of an oculomotor model of alpha activity proposed by Wertheim who demonstrated that alpha reduces during attentive, but not during intentive visual behaviour. The generalisation follows from reports of enhanced alpha in the few seconds prior to a skilled action in sport, and by neurophysiological evidence for a separate cortical organisation for perception and action. Varying proportions of attention and intention then add a dimension to the factors influencing alpha blocking which may explain its inconsistent response.

Hormonal, syndromal and EEG mapping studies in menopausal syndrome patients with and without depression as compared with controls

The aim of the study was to investigate brain function in menopausal depression by EEG mapping, as compared with menopausal syndrome patients without depression and normal controls, and to correlate neurophysiological with clinical and hormonal findings in order to elucidate the pathogenesis of depression in the menopause.

METHODS

One hundred and twenty-nine menopausal women, aged 45-60 years, with no previous hormonal replacement therapy were investigated in regard to hormones (estradiol [E2], follicle stimulating hormone [FSH]), clinical symptomatology (Kupperman Index [KI], Hamilton depression score [HAMD]) and brain function (EEG mapping). Based on KI and DSM-III-R research criteria for major depression, 3 groups were available for statistics (after removal of protocol violators): group A had a KI of <15 and no depression (n = 29); group B had a KI of > or = 15 and no depression (n = 29) and group C had a KI of > or = 15 and fulfilled the criteria for major depression (n = 60).

RESULTS

EEG maps of depressed patients demonstrated less total power and absolute power in the delta, theta and beta band, more relative delta and less alpha power as well as a slower delta/theta and faster alpha and beta centroid than controls, suggesting a vigilance decrement. Group B did not differ from group A. Correlation maps showed significant relationships between estradiol levels and EEG measures (the lower the E2, the worse the vigilance) and between the EEG measures and the Hamilton depression (HAMD) score (the worse the vigilance, the higher the depression score). There were no correlations between the hormones E2 and FSH and the syndromes KI and HAMD. In the target variable, the asymmetry index, depressed patients showed less alpha power over the right than left frontal lobe, whereas normal controls exhibited the opposite. Group B did not differ from group A. The frontal asymmetry index was significantly correlated with the Hamilton depression score and suggests right frontal hyper- and left frontal hypoactivation in depression.

CONCLUSIONS

Although hormonal findings are not directly linked to psychic changes, low estradiol levels do contribute to a decreased vigilance at the neurophysiological level , which is in turn correlated with higher depressive and menopausal symptomatology at the behavioural level. Depression is further correlated to a right frontal hyper- and left frontal hypoactivation.

Task-induced differential cortical activation pattern

Measures of task-dependent cortical activation were assessed by bilateral EEG recordings from frontal, temporal, parietal and occipital areas. Two pictorial tests, the Raven Advanced Progressive Matrices and the Space Relations Test were used for verbal and spatial conditions, respectively. Recordings were obtained for 20 trials of each task from 22 right-handed adult males and 16 s. trial epochs were subjected to Fast Fourier analyses. Averaged intensity values for the alpha band were compared between verbal and spatial tasks for all subjects and between subgroups of verbalizers and visualizers, allotted on the basis of subject's performance index, derived from response speed and accuracy on the two tasks. The results were as follows: (1) The most pronounced EEG discriminators between the two performance subgroups are the left and right parietal and the right frontal area; (2) The left parietal zone provides the most pronounced discrimination between two groups; (3) There were significant interactions between the left parietal and the right frontal region; (4) The two parietal areas show characteristic frequency shifts in opposite directions for the task conditions. The findings imply complex interplay among the two parietal and right frontal areas, associated with sequential and holistic strategies. The results urge researchers to take into consideration subjectively preferred cognitive strategy, which along with objective task demands influences the process of problem solving and accompanying physiological changes.

Multiband topographic EEG analysis of a simulated visuomotor aviation task

Topographic EEG spectral magnitudes from 19 cortical sites were compared in 15 adult male subjects during performance of a simulated flight task and during control conditions which attempted to separately evaluate functional components of this task. Four conditions were studied, including eyes closed, a visual control, a motor control and a simulated landing task requiring integration of both visual and motor components. Each condition was repeated twice in a counterbalanced replicated measures design. A linked-ear EEG reference was used and spectral magnitudes calculated for 6 frequency bands. Decisions concerning band width and spectral transform were empirically determined. Findings indicated no significant differences between replications. A broad posterior cortical suppression of all frequencies was observed in the visual control condition. Anterior sites were affected only in the 7-12 Hz range. Additional suppression was seen during the motor control condition but limited to frontocentral sites in the 11-13 Hz band. The flight task, however, produced a further suppression at centroparietal cortex in the 9-13 Hz range. The extraction of both attentional and motor components from this task suggests that the parietal EEG activation was specific to cognitive processing.

Gender differences in the EEG during cognitive activity

EEG activity of 16 adult volunteers. 8 male and 8 females was monopolarly recorded at P3 and P4 at rest and during solution of three series of tasks: one analytic, one spatial and one mixed demanding both kinds of processing. The following main effects were observed: Men showed significantly higher beta relative power than women, while women showed significantly higher alpha relative power than men during all conditions. Alpha relative power decreased, while theta relative power increased during tasks solution in both sexes. Beta relative power was significantly higher at the left parietal only in men. Interparietal correlation was significantly higher in women than in men during all conditions and bands. For the theta band it increased from baseline values during tasks solution in men, while in women it decreased during the analytic task.

EEG activity during cognitive performance in women

EEG activity of 20 female volunteers was monopolarly recorded at P3, P4, C3 and C4 during four resting periods and three series of cognitive tasks: one analytic, one spatial and one demanding analytical and spatial processing or mixed task. Relative power and inter and intrahemispheric correlations were analysed. Beta relative power was significantly higher during the resting periods at the right parietal and the same pattern of asymmetry was maintained during the three series of tasks. Alpha relative power decreased and theta increased during the three series of tasks regardless of their cognitive nature as compared to baseline. Interhemispheric correlation for theta frequencies, and intrahemispheric correlation for the full band were significantly different during task solution. There were no significant differences between left and right intrahemispheric correlations.

Alpha rhythm and the pineal gland

Alpha rhythm is classically described as a bilateral posterior rhythm of substantially constant frequency in the range of 8-13 Hz which is enhanced by mental relaxation and blocked by attention. Since the full expression of alpha rhythm has been shown to occur coincident with puberty, it is possible that the establishment of alpha rhythm is subject to neuroendocrine influences which govern psychosexual maturation. There is ample evidence to indicate that the pineal gland is implicated in cerebral maturation and psychosexual development. Nocturnal plasma melatonin levels have been shown to decline progressively throughout childhood reaching a nadir at puberty. Since administration of melatonin has been reported to block alpha rhythm, it is proposed that the progressive decline in melatonin secretion during childhood facilitates the maturation of the alpha rhythm. Consequently, the presence of alpha rhythm could be used as a neurophysiological marker for the activity of the pineal gland and disorders associated with absent or delayed maturation of the alpha rhythm such as autism, dyslexia, personality disorders, epilepsy, Tourette's syndrome, and schizophrenia might be related to disturbances of pineal melatonin functions in early life. Moreover, since the EEG patterns associated with cerebral immaturity (i.e., slowing, absence of alpha activity) are more pronounced in the left hemisphere, this hypothesis implies differential influence of the pineal gland on hemispheric maturation potentially accounting for the vulnerability of the left hemisphere to cerebral insults.

EEG spectra in dyslexic and normal readers during oral and silent reading

EEGs of extensively screened dyslexics and normal readers were recorded while they read easy and difficult texts silently and orally, and during two other verbal tasks which also differed in overt speaking but had no reading component: narrative speaking and listening to a story. Mid-temporal, central and parietal leads were referenced to linked ears and to Cz. Large differences between tasks and between groups were found. With the linked ears reference, power was higher in all bands in oral reading than in silent reading, with the largest change occurring in the temporal leads. In the theta and low beta bands the difference between oral and silent reading was greater for controls than for dyslexics. These effects were not accounted for by differences in reading speed or in difficulty. Similar results were found in two cohorts of subjects. The difference between groups in theta was found only in the reading tasks. In contrast, the group difference in low beta was also found in the change from listening to speaking. This implies that the oral-silent group difference in theta is related to some aspect of the reading tasks other than the presence or absence of overt speaking, and that the low beta group difference is related to some aspect of overt speaking rather than to reading per se. With the Cz reference no group differences were found. It is suggested that the groups differ in the reading strategies they use, and the degree to which they shift strategy between the silent and oral tasks. We hypothesize that these cognitive differences are reflected in the theta activity from the temporal lobe. While there were many differences between the tasks in alpha power and asymmetry, no group differences involving alpha were found.

Cerebral activity prior to motion task performance: an electroencephalographic study

Cerebral activity, as reflected by power in the alpha waveband (8-13 Hz), was examined prior to the performance of three tasks with different effort and accuracy requirements. The study aimed to further investigate changes in activity observed in an earlier study in which expert karate performers exhibited significant increases in alpha band power during preparation for a training task. In contrast to the earlier research, the high effort task produced a significant decrease in 'alpha' power prior to performance. 'Alpha' power prior to the high accuracy task showed significant differences mediated by the outcome. Successful performance was preceded by higher levels of 'alpha' power than unsuccessful attempts. The reported use of a cognitive strategy on the first task produced a significant difference in activity, lower alpha power being associated with the use of such a technique.

A new mode of communication between man and his surroundings

The material presented in this paper is the result of a research project that was designed to study the feasibility of establishing an alternative mode of communication between man and his surroundings. The new form of communication proposed uses only the subject's brain waves with no overt physical action required. Subjects' electroencephalograms (EEG) were recorded while they performed various mental tasks designed to elicit hemispheric responses. Features formed from the EEG recording were then used as inputs into a Bayes quadratic classifier to test classification accuracy between the various tasks. The results obtained indicate that it is possible to accurately distinguish between any pair of the five tasks investigated. A comparison between three different methods for creating the feature sets is also presented.

Alpha-contingent stimulation with binocular and monocular viewing

The method of alpha-contingent stimulation was evaluated under conditions of (1) binocular viewing, (2) monocular viewing, dominant eye, and (3) monocular viewing, non-dominant eye. Twelve normal young adults with normal vision and unequivocal alpha rhythms were tested. There was no evidence against generalizing the alpha contingent stimulation (ACS) method to monocular modes of viewing. The same methodological advantages, e.g. reduced random variability of the latency and duration of alpha blocking, were observed for all modes of viewing, which extends the range of possible applications of ACS method.

Asymmetrical brain electrical activity discriminates between psychometrically-matched verbal and spatial cognitive tasks

This study compared the asymmetry of different features of brain electrical activity during the performance of a verbal task (word finding) and a spatial task (dot localization) that had been carefully matched on psychometric properties and accompanying motor activity. Nineteen right-handed subjects were tested. EEG was recorded from F3, F4, C3, C4, P3, and P4, referred to both CZ and computer-derived averaged-ears references, and Fourier transformed. Power in the delta, theta, alpha, and beta bands was computed. There were significant Task X Hemisphere effects in all bands for CZ-referenced data and for the alpha and beta bands for ears-referenced data. The effects were always either greater power suppression in the hemisphere putatively most engaged in task processing or greater power in the opposite hemisphere. Correlations between EEG and task performance indicated that CZ-referenced parietal alpha asymmetry accounted for the most variance in verbal task performance. Power within individual hemispheres or across hemispheres was unrelated to task performance. The findings indicate robust differences in asymmetrical brain physiology that are produced by well-matched verbal and spatial cognitive tasks.

Individual differences in electrodermal and electroencephalographic asymmetries

In a continuing investigation of the relationship between differential hemispheric activation and electrodermal asymmetry, comparisons were made between the electroencephalographic asymmetries and electrodermal asymmetries exhibited by subjects carrying out particular tasks. Bilateral skin conductance responses and 28 channels of EEG data allowing the production of topographical maps were collected from 8 female and 8 male right-handed subjects during the performance of two tasks, one verbal and one visuospatial. The tasks were selected with the aim of differentially activating the hemispheres to investigate whether parallel changes in the direction of electroencephalographic and electrodermal asymmetries would occur. EEG asymmetries were compared in female and male subjects. Previous research has indicated that males tend to show stronger EEG asymmetry than females, and that this is emphasised in verbal tasks. This was confirmed by the present study. Comparison with electrodermal activity revealed a weak relationship between the two measures, with some parallels between task-related variations in the beta 2 waveband and skin conductance responses. No parallels between alpha activity or skin conductance level were demonstrated. If the subjects are regrouped according to degree of electrodermal asymmetries, then some closer parallels with electroencephalographic asymmetries are revealed with more marked electrodermal asymmetry paralleling more marked electroencephalographic asymmetry. Variations in electrodermal asymmetry appear to be related to greater activity on the hand contralateral to the hemisphere showing smaller amplitude EEG activity, generally in the beta waveband. In discussing cortical control of electrodermal activity, these findings are discussed in terms of both the contralateral excitatory and the contralateral inhibitory models.

Hemisphere asymmetry of alpha burst sequential organization in depression

A new quantitative EEG index based on the sequential variability of the frequency of occurrence of alpha bursts (alpha-BVI) was utilized for investigating the respective role of the two hemispheres in depression and their relationship with two clinical dimensions of this illness: psychomotor retardation and blunted affect. The EEG (at P3 and P4 referred to Fz) was recorded during rest periods in two groups of patients selected according to their scores on various clinical scales: one consisted of 12 patients characterized by psychomotor retardation (PMR group), the other of 9 patients characterized by blunted affect (BA group). A control group of 12 normal subjects was recorded in the same conditions. All subjects were dextral. The following main results were obtained: (1) in both groups of patients the right and the left alpha-BVI were, before treatment, significantly lower than those of the controls. (2) In controls, the sequential alpha burst variability was identical on both hemispheres. (3) In patients, before treatment, the right hemisphere alpha-BVI was significantly lower than the left. (4) Electro-clinical correlations were also observed: (A) in the BA group, before treatment, (a) between the degree of blunted affect and the decrease of the right alpha-BVI, (b) between ideoverbal retardation and the decrease of the left alpha-BVI (these correlations disappeared after treatment); (B) in the PMR group, ideoverbal retardation was, on the contrary, correlated to a right alpha-BVI decrease, this correlation persisting after treatment. These results are discussed according to the role of each hemisphere in depression.

Event-related covariances during a bimanual visuomotor task. I. Methods and analysis of stimulus- and response-locked data

A new method that measures between-channel, event-related covariances (ERCs) from scalp-recorded brain signals has been developed. The method was applied to recordings of 26 EEG channels from 7 right-handed men performing a bimanual visuomotor judgment task that required fine motor control. Covariance and time-delay measures were derived from pairs of filtered, laplacian-derived, averaged wave forms, which were enhanced by rejection of outlying trials, in intervals spanning event-related potential components. Stimulus- and response-locked ERC patterns were consistent with functional neuroanatomical models of visual stimulus processing and response execution. In early post-stimulus intervals, ERC patterns differed according to the physical properties of the stimulus; in later intervals, the patterns differed according to the subjective interpretation of the stimulus. The response-locked ERC patterns suggested 4 major cortical generators for the voluntary fine motor control required by the task: motor, somesthetic, premotor and/or supplementary motor, and prefrontal. This new method may thus be an advancement toward characterizing, both spatially and temporally, functional cortical networks in the human brain responsible for perception and action.

Lateral eye movements as an indication of hemispheric preference: an EEG validation study

The hemispheric asymmetry model of lateral eye movements (LEM), hypothesizing a relation between a predominance of lateral gazes to one side with a predominance of activity in the hemisphere contralateral to the preferred direction of gaze, was tested in male, right-handed subjects. During presentation of cognitive tasks (verbal synonym tasks and spatial orienting tasks) the decrease in alpha-power from a reference period to each of four activation periods (anticipation, task-presentation, first LEM, answer) for 6 derivations from each hemisphere was calculated using the method of 'Event-related desynchronisation'. Evidence for the hypothesis was found only during the EEG-epoch one second before the answer. Discrimination between subjects with a predominance of left vs right eye movements (left- vs right-movers) was best at temporal (T3, T4) and central (C3, C4) sites. These results were significant for the entire alpha-band (8-12 Hz) and--even more pronounced--for the alpha-2-band (10-12 Hz). The alpha-1-band (8-10 Hz) did not produce significant differences. Comparing the two types of tasks, synonym tasks yielded results which were more congruent with the hypothesis. The results suggest that lateral eye movements indicate individual differences in hemispheric EEG-asymmetries under certain experimental conditions (task, segment of EEG-analysis, site, frequency band).

Modification of EEG asymmetry induced by auditory biofeedback loop during REM sleep in man

Several studies have emphasized the relationship between (1) rapid eye movement sleep (REM sleep) and learning, and (2) between REM sleep and asymmetry in EEG activity. Since we have shown that obtaining operant conditioned responses via auditory biofeedback during REM sleep is feasible, we demonstrate here that REM contingent auditory stimulations (white noise stimulation or interruption of a continuous white noise stimulation) lead to differential changes in phasic and tonic components of REM sleep. Whereas during baseline nights a relative right activation is found in the medium bands of EEG frequencies, our procedure seems to induce a systematic interhemispheric change during experimental nights. A new approach to the information processing hypothesis during REM sleep is proposed in terms of functional lateralized modifications of the EEG.

Task-related EEG asymmetries: a comparison of alpha blocking and beta enhancement

Alpha and beta content of spectrally analyzed EEG were used to assess differential hemispheric engagement during two linguistic tasks (semantic and phonetic) and one acoustic task involving detection of target items embedded within the same stimulus series. Beta content of the EEG increased reliably in the left hemisphere during the linguistic tasks, whereas the expected attenuation or blocking of alpha did not occur reliably. These data suggest that left hemisphere beta enhancement rather than alpha blocking is a more efficient index of differential hemispheric engagement during language processing.

Sex task and processing strategy effects in hemispheric alpha asymmetries for the recall and recognition of arousal words: results from perceptual and motor tasks in males and females

Hemispheric alpha asymmetries of males and females were observed during perceptual and motor tasks requiring recall and recognition of words controlled for level of arousal (positive, negative, and neutral). Verbal reports of individual processing strategy were collected and analyzed relative to hemispheric alpha ratios. Results showed greater alpha suppression in the left relative to right hemisphere for recall as compared to recognition tasks and for word presentation when contrasted with motor conditions. High positive correlations were found between narrative report of processing strategy and hemispheric alpha data. A separate analysis revealed that seven subjects identified as highly analytic processors showed greater alpha suppression in the left relative to right hemisphere across tasks, conditions, and stimuli than did seven highly visual processors who, in contrast, demonstrated greater right hemispheric alpha suppression. Task difficulty and individual differences in processing style that modify cerebral laterality effects are discussed.

Hemisphere functioning and motor imitation in autistic persons

Previous research has found that a high proportion of autistic individuals exhibit an atypical pattern of hemispheric specialization suggestive of impaired left hemisphere functioning: namely, right hemisphere dominance for both verbal and visual-spatial processing. Studies of brain-damaged persons have suggested that the left hemisphere is specialized for the use of nonverbal gesture. Since a major characteristic of autism is an impairment in the use of gesture, it was predicted that autistic persons would also show atypical hemispheric specialization for motor imitation. To test this hypothesis, hemispheric activation was measured using EEG recordings of alpha rhythm in autistic and matched normal control subjects during four motor imitation tasks. Autistic subjects showed significantly greater right hemisphere activation during the imitation tasks, than normal subjects. This pattern was particularly evident in younger autistic subjects and during oral, rather than manual, imitation tasks.

EEG asymmetry in schizophrenic patients before and during neuroleptic treatment

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 alpha asymmetry: task difficulty and hypnotizability

Parieto-occipital EEG alpha was recorded bilaterally, while 20 high- and 20 low-hypnotizable women performed one left-hemisphere and one right-hemisphere task of low difficulty and two other comparable tasks of high difficulty. Every task was performed twice, once with eyes open and once with eyes closed. All subjects were right-handed. The tasks were originally selected to be of high and low difficulty. The subjective rating of task-difficulty was also evaluated. The integrated amplitude alpha and the alpha ratio (R-L/R + L) were the dependent variables. The highly hypnotizable women showed significantly higher alpha amplitude in eyes-closed condition than the low scorers; this difference disappeared during task performance and in the eyes-open condition. The left-tasks showed lower alpha amplitude in both hemispheres than right-tasks and baseline. The right-hemisphere alpha amplitude was lower than left in all experimental conditions. On tasks of high and low difficulty there was different hemispheric behavior on right and left tasks. Performance reflecting the right and left hemispheres in the low-difficulty condition showed no changes between baseline, right- and left-tasks, while under high difficulty there was a decrease in alpha amplitude in the right and even more marked decrease in the left hemisphere during left-tasks. The pattern of task effects for ratio scores was the same as for alpha amplitude, however, despite the analysis of alpha scores, an interaction of hypnotizability X task-difficulty was detected. The highly hypnotizable women showed less negative alpha ratio during a task of low difficulty than during tasks of high difficulty; the reverse was true for the low-hypnotizable women. Finally, the highly hypnotizable subjects showed less subjective difficulty during performance than the low scorers.

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 correlation topography in poor spellers

Twenty-three poor spellers (average age 13 years) and 21 matched controls were studied. The EEG from 6 derivations was quantified using Hjorth's parameters 'Activity' and 'Mobility,' from which product-moment correlations were calculated between derivations. Cross-correlations were analogously calculated from EEG amplitude values. In poor spellers higher Mobility local correlation indices (LCIs) occurred in the right fronto-central derivation during reading. Moreover, significantly more right hemisphere dominant Mobility LCIs were seen in the fronto-central regions during reading in poor spellers as well as in the groupings of prepubertal boys and neonatal risk cases. This seems to be the effect of a more right hemisphere dominant activation of the cortical regions during reading. During rest, poor spellers had a less posteriorly accentuated distribution of Activity and cross-correlations than controls, assumed to be the effect of different distributions of alpha activity in the two groups.

Modification of REM sleep behavior by REMs contingent auditory stimulation in man

Following studies about supposed relationship between rapid eye movement sleep (REM sleep) and learning, a new approach, based on operant conditioning is introduced. We demonstrate that rapid eye movements (REMs) contingent auditory stimulation in man leads to some consistent (quantitative and qualitative) modifications of REM sleep behavior. Stimulating REMs in the frame of a continuous reinforcement schedule increases total REM sleep duration but decreases REMs density, and modifies hemispheric EEG symmetry. The contrasting effects of such sensory stimulations and results related to information processing hypothesis are discussed.

Attention to television: intrastimulus effects of movement and scene changes on alpha variation over time

Central and occipital EEG alpha were used as an on-line measure of momentary changes in covert attention during television viewing. Alpha was recorded during nine 30-second commercials shown embedded in a half-hour situation comedy. Two time series were constructed for data analysis. A stimulus series consisted of codes representing the presence or absence of scene changes or person and object movement for each half-second interval of the commercials. The alpha series consisted of median alpha scores for each half-second interval, aggregated across 26 subjects. The alpha series was regressed on the movement and scene change series, both of which produced significant increments in R, even after autocorrelational effects inherent in the alpha series were removed. As a validity check on the attentional interpretation of alpha, it was shown that mean alpha for each commercial was significantly (negatively) correlated with recall and recognition of commercial contents. The results are discussed in terms of their implications for further use of continuously-recorded alpha in research on factors that influence attention to television.