Lateralized Cognitive Processes and the Electroencephalogram

A cognitive and neurophysiological test of change from an individual's baseline

OBJECTIVE

An automated cognitive neurophysiological test is presented that characterizes how an individual was affected by a drug or treatment. The test calculates sub-scores for working memory task performance, cortical activation, and alertness, and combines the sub-scores into an overall score.

METHODS

The test was applied in a double-blind, placebo-controlled study of alcohol, caffeine, diphenhydramine, and sleep deprivation in 16 healthy adults.

RESULTS

The between- and within-day variability of the sub-scores and overall scores for placebo were all near zero, suggesting that the scores are stable. All treatments affected the overall score, while differential effects on sub-scores highlighted the added value of EEG measures.

CONCLUSIONS

The test is sensitive to relatively mild alterations in cognitive function. Its automation makes it suitable for use in large-scale clinical trials.

SIGNIFICANCE

By combining task performance with EEG brain function measures, the test may prove to have better sensitivity and specificity in detecting changes due to drugs or other treatments than comparable neuropsychological test batteries that do not directly measure brain function signals.

Interhemispheric asymmetry of EEG alpha activity at rest and during the Wisconsin Card Sorting Test: relations with performance

There are conflicting results regarding the functional asymmetry of the prefrontal cortex. Spectral power analysis of electroencephalographic (EEG) activity can provide important clues about the cortical mechanisms. In this study, interhemispheric EEG alpha power asymmetry of healthy individuals was investigated during the execution of the Wisconsin Card Sorting Test (WCST) and during rest. We analyzed alpha-1 (8.6-10.2 Hz) and alpha-2 (10.9-12.5 Hz) bands separately and found some evidence to indicate that lower and upper alpha bands reflect different cortical processes. On the other hand, greater alpha power during resting correlated with higher performance on the WCST. The lower left frontal alpha power during WCST correlated significantly with the higher WCST performance. However, greater bilateral parietal alpha power during WCST correlated with higher performance. Significant correlations between EEG activity and WCST performance were, in general, restricted to lower alpha power, both at rest and during the task. These findings are discussed with regard to attention processes reflected by lower alpha activity.

[Determination of language dominance using EEG spectral analysis versus the Wada test in temporal epilepsy (right-handed subjects)]

Spectral analysis of the EEG alpha rhythm was studied in nine temporal epileptic right-handed patients in order to predict localization of the speech area. We studied the variation of the spectral power of the alpha rhythm during an activation paradigm previously validated in normal right-handed subjects. Significant alpha power decreases in the left hemisphere during writing with the right hand (as compared to resting) and/or significant alpha power decreases in the right hemisphere during left-hand recognition and classification of cardboard objects (as compared to resting) were considered as consistent with left-hemisphere dominance for language. The results of EEG spectral analysis were compared with those of the Wada test. The left hemisphere was dominant for language according to the Wada test in eight subjects and the right hemisphere in one subject. Six patients had a significant alpha power reduction in the hemisphere concerned during lateralized cognitive tasks, consistent with language localization in the left hemisphere according to the Wada test. The three remaining patients had no significant EEG spectral power variations. A significant decrease of alpha power in the active hemisphere during cerebral activation seems statistically related to left-hemispheric dominance for language in right-handed subjects (hemispheric specialization). However, the localization of the speech area using this electrophysiological method does not appear clinically relevant for a case-by-case decision in individual patients.

Cortical distribution of EEG activity for component processes during mental rotation

Alpha power (8-12 Hz) was monitored over the frontal, temporal, parietal and occipital lobes of the left and right cerebral hemispheres while participants mentally rotated three-dimensional shapes to match a specified target. By comparing the activational patterns generated during three experimental conditions, each designed to systematically isolate the involvement of the various subcomponents comprising this mental rotation task, it was suggested that the right frontal lobe mediates encoding and comparison/decision processes, while the left parietal and the left temporal region appear most involved in the generation of images and their mental rotation. A preliminary model describing the cooperative interaction of these cortical regions during mental rotation tasks is proposed.

Perception of motion and qEEG activity in human adults

This study was designed to relate visual perception of motion to cortical activity, by evaluation of the association of quantified electroencephalogram (qEEG) parameters with a video film projection. The EEG was recorded from 14 sites according to the International 10-20 system and a common average reference was used. Forty right-handed volunteers (mean age = 24 years) were examined. The video film consisted of 20 s sequences showing still shots and moving shots with human movements or object movements. The EEG was then subjected to spectral analysis; the spectral powers for the theta, alpha and beta bands were calculated for 14 s epochs and compared with sequences of the video film. All analyses were based on logarithmically transformed absolute spectral power values. The power values of each frequency band were analysed in a 3-way repeated measure ANOVA (Hemisphere x Electrode x Sequence). The results were represented by EEG cartography. Significant decreases in the alpha 1, beta 1 and beta 2 power values of EEG in centro-parietal regions of both hemispheres were shown during perception of human motion sequences. This suggests participation of the sensorimotor cortex during visual observation of human motion.

The future of electroencephalography in assessing neurocognitive functioning

High temporal resolution is necessary to resolve the rapidly changing patterns of brain activity underlying mental function. Additionally, simple, non-intrusive equipment is needed to routinely measure such functions in doctors' offices, at home and work and in other naturalistic contexts as people perform normal everyday activities. When compared with all other modalities for measuring higher brain functions, EEG is unique in that it has both these attributes. Two factors are limiting the further development and application of EEG for measuring cognitive functioning: a technical one that is easy to overcome and a sociological one that is more problematic. The technical limitation is that traditional EEG technology and practice provides insufficient spatial detail to identify relationships between brain electrical events and structures and functions visualized by magnetic resonance imaging (MRI) or other modalities. Recent advances overcome this problem by recording EEGs from more electrodes, by registering EEG data with anatomical information from each subject's MRI, by correcting the distortion caused by volume conduction of EEG signals through the skull and scalp, and by computing hypotheses about the sources of signals recorded at the scalp. The sociological limitation is that clinical EEGs are mostly performed by neurologists with no particular special interest in cognitive brain function, while cognitive research using EEG is largely done by psychology professors and their graduate students with no clinical ambitions. The diminishing clinical role of traditional EEGs in localizing lesions in the brain, and the obvious and insistent medical need for inexpensive and accessible tests of cognitive brain functioning may serve to soon dissipate this sociological obstruction. This will lead to a golden age of EEG in which Hans Berger's vision of the EEG as a window on the mind will be realized. Rather than slowly fading into obsolescence, EEG will retain its role as the primary means of measuring higher brain function when the purpose is not 3D localization per se, and will serve as an invaluable complement to functional MRI in those instances when both high temporal and high spatial resolution are required.

Sex Differences in Matching Circles and Arcs: A Preliminary EEG Investigation

Alpha wave (8-12 Hz) activity was monitored over the four lobes of the left and right cerebral hemispheres while 12 male and 12 female participants mentally manipulated circles and arcs to determine size matches. Four task conditions were tested, each designed to tap into the visual encoding, image generation, mental rotation, and comparison/decision subcomponents comprising this task. Males were more accurate than females in making such matches, and in all conditions they exhibited a significant alpha power reduction asymmetry, with the right frontal lobe being more active than the left frontal lobe. Females showed a pattern of activation that was bilaterally distributed, primarily to the frontal and temporal regions. These findings suggest a difference in the functional organisation of the male and female brain which may contribute to the reported sex difference in the performance of some spatial tasks.

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.

Electrophysiological analysis of the registration, storage and retrieval of information in delayed matching from samples

Brain processes of registration, storage in working memory and retrieval of different kinds of information were studied by analysis of EEG and ERP activity recorded during two delayed matches from sample tasks: (1) matching the digits in two series of six numbers, and (2) matching the sums of the same two series of six numbers. each trial was composed of six intervals continuing six equally spaced visual stimuli: (1) control--observing a series of six fixation points, P1, on a computer monitor; (2) priming--viewing a series, S1, of six numbers; (3) delay--observing a second series of six fixation points, P2; (4) matching--viewing a second series, S2, of six numbers; (5) response selection--selecting the left button to press if S1 contained all the items in S2 or the right button if any item appeared only in S2, while observing six fixation points; (6) feedback--six color coded fixation points indicate correct or error. Each interval was 4 s in duration and 20 trials were presented in each task. During each interval the visual field flickered at a tracer frequency of 1.5/s, whether numbers or fixation points were on the monitor screen. Very narrow band power spectra (VNB), ERPs elicited by presentation of S1 or S2 information items, and non-contingent probes (NCP) elicited by presentation of fixation points were used to trace the processing of information by neural populations activated by the visual stimulation. Global field power maxima identified latencies at which functional landscapes were analyzed. VNB, ERP, NCP and landscape differences were found between digits and sums. However, though these differences were highly significant within each subject (p < 0.001), no consistency was found across individuals for the electrophysiological changes during the tasks. This suggests that utilization of brain resources in cognition varies greatly with individual cognitive styles and strategies.

Mapping cognitive brain function with modern high-resolution electroencephalography

High temporal resolution is necessary to resolve the rapidly changing patterns of brain activity that underlie mental function. While electroencephalography (EEG) provides temporal resolution in the millisecond range, which would seem to make it an ideal complement to other imaging modalities, traditional EEG technology and practice provides insufficient spatial detail to identify relationships between brain electrical events and structures and functions that are visualized by magnetic resonance imaging (MRI) or positron emission tomography (PET). Recent advances overcome this problem by recording EEGs from more electrodes, by registering EEG data with anatomical information from each subject's MRI, and by correcting the distortion that is caused by volume conduction of EEG signals through the skull and scalp. Along with its ability to record how brains think when performing everyday activities in the real world, these advances make modern EEG an invaluable complement to other functional neuroimaging modalities.

Motor programming in both hemispheres: an EEG study of the human brain

Differential hemispheric involvement in controlling simple and complex motor movements was investigated in humans using EEG spectral responses. Analysis of spectral power in the alpha band revealed the following. While during a simple motor task (tapping) signs of unilateral cortical activation were present, more complex sequential motor behaviour (Luria finger apposition task) led to symmetrical bihemispheric activation. It appears that unilateral cortical processing is present in the normal brain when very simple computations are performed. Bilateral hemispheric activity and interhemispheric interaction may be general features of more complex information processing in the cortex.

Localization of activated areas and directional EEG patterns during mental arithmetic

In a search for the physiological correlates of mental activity, localized EEG desynchronization induced by mental arithmetic was assessed by the entropy of the EEG power spectrum (irregularity index II). The topographic mapping of II can show a localized cortical activation. Directional EEG patterns during mental arithmetic were further examined with a directed mutual information measure (information flow). These two information measures were compared between resting and mental arithmetic conditions in 10 right-handed subjects as well as one left-handed subject. II significantly increased during mental arithmetic in the left temporo-centro-parietal region in right-handed subjects, thus exhibiting its activation. Significant changes in information flow during mental arithmetic were found in the directions mostly from the temporo-centro-parietal region to other areas and within the frontal region in right-handed subjects: information flow from the left temporal and the mid-frontal areas increased and information flow mostly from the left hemisphere decreased. One left-handed subject showed greater II in right post-temporal area. These findings suggest that the left temporo-centro-parietal activation is specific to calculation processing, and the frontal information flow is related to the active performance of mental arithmetic.

Influence of lateral gaze on electroencephalographic spectral power

The effects of maintaining lateral gaze (as opposed to looking straight ahead) on electroencephalographic spectral power were tested in 12 right handed male subjects during eye opening (EO) and eye closure (EC). Our working hypothesis, based on Kinsbourne's paradigm, was that maintaining right lateral gaze activates the left hemisphere while maintaining left lateral gaze activates the right hemisphere, this activation resulting in a reduction in the spectral power over the hemisphere in question. Results showed that the variations in spectral power involved mainly the alpha frequency band. In the EC condition, the results were consistent with our working hypothesis: right lateral gaze produced a marked reduction in left hemispheric spectral power. In the EO condition, alpha power was constantly higher in the right hemisphere whether lateral gaze was maintained to the right or to the left. This can possibly be due to an attentional effect. Results are discussed with regard of the type of alpha rhythm and of the activation of cortical oculomotor centres. They shed light on the controversy concerning the existence of specific EEG correlates of cognitive activity, which preferentially involve each of the cerebral hemispheres.

Influence of lateralized neuropsychological activities with and without sensorimotor components on EEG spectral power (alpha-rhythm)

Spectral analysis of the EEG (alpha-rhythm) was studied in 8 young right-handed men who underwent 6 experimental tasks which were compared with rest, and included two pure motor activities using only the right and then the left hand, two pure neuropsychological tasks, and two "mixed" tasks with both neurophysiological and motor activities. The electrophysiological parameters studied were the log of spectral power and an asymmetry index (RP-LP)/(RP + LP). In order to demonstrate lateralization of the EEG, one must associate lateralized motor and neuropsychological tasks (which are supposed to preferentially involve one of the cerebral hemispheres). These results may reconcile apparently divergent views published in the literature with respect to lateralized EEG modifications associated with cognitive activities.

EEG coherence during hemispheric activation in schizophrenics

We studied the change of EEG alpha-band coherence between resting and motor performance ("reactivity of EEG coherence") in 18 chronic schizophrenics and 30 normal controls, examining differences between left and right hemisphere tasks. Three coherences were examined for each hemisphere. The central-parietal coherence in normals increased on the left for left hemisphere tasks, and decreased on the right for right hemisphere tasks, whereas the patients showed a decrease of both measures, more on the left side. Thus, the interhemispheric difference of central-parietal coherence reactivity was reversed for the schizophrenics (P less than 0.06) and suggested a left-sided deviation. The lateral-percentral and precentral-central coherences showed no left-right deviations of reactivity in the patients. Since coherence increase is considered to be a sign of the coupled function between the studied regions, our findings suggest a defective coordination of left central-parietal regions during a task in schizophrenics.

Topographical EEG differences between schizophrenic patients and controls during neuropsychological functional activation

Ten DSM III schizophrenic patients belonging to an Active syndrome were compared with 10 age- and sex-matched normal controls on neuropsychological tests with concurrent monitoring of topographical EEG using a brain imager with a 28-electrode array. In line with predictions, abnormalities in patients were found in tests involving right hemispheric functions. Deficits were found in recognition memory for faces as distinct from a verbal recognition memory task. Right temporo-parietal involvement in the faces task was confirmed by an absence of beta II amplitude reduction in patients compared with controls in the right temporo-parietal region. A similar anomaly occurred in patients in a left- but not right-hand finger-thumb apposition test in left anterior and right posterior regions, and also in a passive visual fixation task where it was located bilaterally in the occipito-parietal region. Functional activation with neuropsychological tests holds promise as one approach to the validation of topographical mapping of brain electrical activity.

Influence of lateralized sensorimotor and neuropsychological activities on electroencephalographic spectral power

In order to test the effect of 'lateralized' sensorimotor and neuropsychological activities on EEG spectral power (P), we recorded EEGs over the right and left central regions with 3 different derivations C5P3/C6P4, C5Cz/C6Cz, and C5 ears-linked (EL)/C6EL in 14 young, right-handed men who underwent ten 2 min sequences including 4 during rest (3 with eyes closed (EC), 1 with eyes open (EO], and 6 during tasks reputed to involve preferentially the left (Le) or the right (Ri) hemisphere, i.e., pure left and pure right motor activity of the hand (EC), pure neuropsychological tasks consisting in lexical followed by spatial form analysis and finally mixed (neuropsychological and motor) EC tasks consisting in writing followed by left hand object recognition. Three spectral parameters P, log P and asymmetry index AI = (P Ri-P Le)/(P Ri + P Le) were calculated in 5 frequency bands theta, alpha 1, alpha 2, alpha 3 and beta 1. We observed a relationship between task complexity and P reduction on both hemispheres which was greater during rest, less during motor activity and least during mixed motor and neuropsychological activities; during EC activities more specifically involving the left hemisphere, only the comparison between rest and mixed sequences was significant. During EC activities involving the right hemisphere, both motor and mixed sequences were significantly different from rest sequences. In addition, during the EO sequences, P was usually greater than during rest. As compared to rest conditions, the AI increased during sequences preferentially involving the left hemisphere and decreased during preferentially right hemisphere activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectral analysis of the EEG (alpha rhythm) and activity in the left hemisphere: the effects of lateral gaze

This study tests the effect of maintaining right and left lateral gaze during a writing task which preferentially implicates the left hemisphere using an asymmetry parameter calculated from the spectral power of the alpha rhythm (RP-LP/RP + LP) in a right-handed patient undergoing the same experimental regimen nine times. A six derivation EEG was recorded. Maintaining left lateral gaze (toward the active hemisphere) removes the lateralization found during writing while staring straight ahead whereas maintaining right lateral gaze (toward the side opposite the active hemisphere) results in slightly lower values which are however, not significantly different from those obtained during staring straight ahead. This study adds an electrophysiologic aspect to Kinsbournes's paradigm on gaze position and hemispheric activation.

Inter- versus intra-subject variance in topographic mapping of the electroencephalogram

The variability of the normal topographic EEG distribution between a quiet, eyes closed, resting state and the performance of cognitive tasks (listening to a story or music) was studied in 20 normal (10 male) right-handed college students or graduates ages 18-40 yrs. Amplitude changes in the topographic frequency distribution (2.5-7 SD) of alpha frequency band (8-13 Hz) were noted between tasks and resting state in individual subjects. When group data for the resting versus listening states were compared, no statistical differences could be demonstrated. The group variability was 50% of the power of the resting record. Repeat studies in 10 subjects demonstrated a test-retest variance of 10% of the mean individual power. The data suggest that inter-subject differences in the alpha frequency and individual topographic differences will require careful normalization for development of baseline "brain maps" to serve as a standard for investigation of disease states.

Cognitive and task-related EEG correlates of arithmetic performance in adolescents

Cognitive and neurophysiological correlates of arithmetic calculation, concepts, and applications were examined in 41 adolescents, ages 12-15 years. Psychological and task-related EEG measures which correctly distinguished children who scored low vs. high (using a median split) in each arithmetic subarea were interpreted as indicative of processes involved. Calculation was related to visual-motor sequencing, spatial visualization, theta activity measured during visual-perceptual and verbal tasks at right- and left-hemisphere locations, and right-hemisphere alpha activity measured during a verbal task. Performance on arithmetic word problems was related to spatial visualization and perception, vocabulary, and right-hemisphere alpha activity measured during a verbal task. Results suggest a complex interplay of spatial and sequential operations in arithmetic performance, consistent with processing model concepts of lateralized brain function.

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.

Electroencephalographic spectral power and lateralized motor activities

The powers of the theta (3.5-7 Hz), alpha (7.4-12.3 Hz) and beta 1 (12.9-14.8 Hz) rhythms were analysed in symmetrical derivations. Sixteen right-handed young male adults were observed: at rest, with eyes closed (EC) (4 sequences) and eyes open (EO) (4 sequences); during right then left tonic alternate or sequential movements of the hand and while gazing to the right then to the left. At rest there exists a clear and significant spectral dominance to the right which does not appear in all the rhythms or in all the derivations. As far as the alpha rhythm EC is concerned, individual analysis of the sequences shows that of those which are significantly lateralized, three-quarters are lateralized towards the right. Right motor activity exaggerates, left motor activity diminishes, this right electrical dominance. Lateral gaze is the most powerful activity in this respect. At each derivation, comparison of intensities during right and left activities shows that the contralateral movements diminish the spectral power in the 3 bands studied. This effect seems to be obtained most frequently at the centro-parietal level. The spectral power at rest compared with that during motor activity is higher constantly for theta rhythm, in almost half the cases for the alpha and occasionally for the beta 1.

Remote effects of cerebrovascular accidents: visual evoked potentials and electrophysiological coupling

Performance on two electrophysiological tasks, EEG and VEP, of patients who had sustained either a right or left middle cerebral artery CVA was examined. The occurrence of a stroke disrupted electrophysiological functioning of brain regions beyond the ischemic focus of the CVA, and these remote effects persisted beyond the period of transient diaschisis. CVA reduced the electrophysiological concordance between brain regions as reflected in EEG coupling and VEP intercorrelation procedures, and the disruption was more severe if the CVA affected the right as opposed to left middle cerebral artery. Techniques for characterizing the abnormal event-related potentials of CVA subjects are reviewed, and some possible theoretical explanations of the functional communication and remote effects are offered.

Shadows of thought: shifting lateralization of human brain electrical patterns during brief visuomotor task

Dynamic spatial patterns of correlation of electrical potentials recorded from the human brain were shown in diagrams generated by mathematical pattern recognition. The patterns for "move" and "no-move" variants of a brief visuospatial task were compared. In the interval spanning the P300 peak of the evoked potential, higher correlations of the right parietal electrode with occipital and central electrodes distinguished the no-move task from the move task. In the next interval, spanning the readiness potential in the move task, higher correlations of the left central electrode with occipital and frontal electrodes characterized the move task. These results conform to neuropsychological expectations of localized processing and their temporal sequence. The rapid change in the side and site of localized processes may account for conflicting reports of lateralization in studies which lacked adequate spatial and temporal resolution.

Drawing and the cerebral hemispheres: bilateral EEG alpha

Bilateral EEG alpha (alpha) was measured during several cognitive tasks in two experiments. EEG alpha was suppressed relative to baseline in both hemispheres during every drawing and writing task. In addition, there were task-related EEG alpha asymmetries. Differences in left-hemisphere, but not right-hemisphere EEG alpha activity, were responsible for EEG alpha asymmetry differences between writing and drawing tasks. There was no difference in bilateral EEG alpha during drawing an upright versus an inverted drawing stimulus; failing to support Edward's (1977, 1979) 'cognitive shift' approach to drawing instruction.

Event related brain electrical and magnetic activity: toward predicting on-job performance

Personnel assessment has depended on paper and pencil tests. These tests are able to predict academic performance fairly well, but have been criticized for their ineffectiveness in predicting on-job performance. Research on brain function which emphasizes "process" rather than "content" variables, may be able to predict on-job performance better than traditional tests. Relationships have been found between event related brain potentials (ERPs) and performance in fighter aircraft and on a sonar simulator, as well as enlistees promotions and attrition. Research has suggested that ERP records are better able to discriminate and classify performance groups than paper-and-pencil test scores. Biomagnetic data are described from heart and brain. These data suggest increased sensitivity to individual differences, and may offer greater opportunity for improving prediction of on-job performance, than ERP records or paper-and-pencil tests.

Dissociation of alpha and theta activity as a function of verbal and visuospatial tasks

EEG was recorded from P3 and P4 in 12 male subjects during a rest condition and while they performed a verbal and a visuospatial task. Power in the alpha and theta bands was derived from EEG epochs associated with task-related cognitive activity uncontaminated by response activity. Alpha power was significantly lower during performance on both tasks compared to the rest condition, but did not differ between tasks or hemispheres. Conversely, theta power was significantly higher during task performance, and, in the right hemisphere only, was higher in epochs recorded during the visuospatial as opposed to the verbal task. This difference between the tasks in right hemisphere theta correlated significantly with level of visuospatial performance as, to a lesser extent, did differences in left hemisphere theta. These results are discussed in terms of the sensitivity of different regions of the EEG spectrum to cognitive activity underlying performance on different types of task.

Electrical potentials in human brain during cognition: new method reveals dynamic patterns of correlation

A new technique has been developed for identifying, in humans, dynamic spatiotemporal electrical patterns of the brain during purposive behaviors. In this method, single-trial time-series correlations between brain macropotentials recorded from different scalp sites are analyzed by distribution-independent mathematical pattern recognition. Dynamic patterns of correlation clearly distinguished two brief visuomotor tasks differing only in type of mental judgement required (spatial or numeric). These complex patterns shifted in the anterior-posterior and left-right axes between successive 175-millisecond intervals, indicating that many areas in both cerebral hemispheres were involved even in these simple judgements. These patterns were not obtainable by conventional analysis of averaged evoked potentials or by linear analysis of correlations, suggesting that the new technique will advance the study of human brain activity related to cognition and goal-directed behaviors.

Alpha asymmetry as a function of cognitive mode: the role of lateral eye movements

When monitored concurrently, the spontaneous lateral eye movements and alpha asymmetry associated with mental activity were themselves interrelated. Left eye movements were associated with a decrease in the ratio of right to left hemisphere alpha, while right eye movements resulted in an increase in this ratio, independent of cognitive task. The results were interpreted as evidence for a direct effect of oculomotor activity on alpha asymmetry.

The use of brain electrical potentials (BEP) to study localization of human brain function

Various techniques such as neuropsychological diagnosis of individuals with focal lesions, stimulation of neurosurgery patients, and regional cerebral blood flow have been used to elucidate the major anatomical and functional divisions of the human cerebral cortex. Because of insufficient spatial sampling and other limitations, only minor support for these divisions comes from brain electrical potential (BEP) experimentation. The use of EEG to localize different neuropathologies and to screen and track the evolution of seizure disorders is fairly reliable and still widely practiced. Its use, however, in localizing higher cognitive functions is much more complicated and has not stood the test of scientific scrutiny because of methodological problems. More specifically, the failure to control for the stimulus, response and performance related properties of tasks in experiments has rendered ambiguous the results of most EEG studies of higher cognitive functions. Those studies which actually controlled for these properties did not find and differences between tasks.