Lateral specialization of cognitive mode: II. EEG frequency analysis

EEG activity during cognitive processing: influence of attentional factors

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

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.

Differential lateralization for positive and negative emotion in the human brain: EEG spectral analysis

The present experiment utilized EEG spectral analysis to investigate lateralization for emotional processes in the human brain. In frontal zones, a differential lateralization for positive and negative emotion was observed, with relative left-hemispheric activation (as measured by decreases in alpha abundance) for positive emotions and relative right-hemispheric activation for negative emotions. In parietal zones, a differential lateralization for verbal and spatial processes was observed, with relative left-hemispheric activation for verbal questions and relative right-hemispheric activation for spatial questions. Examination of EEG bands other than alpha (i.e. delta, theta, beta, and total power) suggested that emotional and cognitive processes are further distinguished by different EEG spectral patterns.

EEG time and frequency domain measures of cerebral specialization

Electroencephalographic (EEG) studies of lateralized cognitive functions have primarily relied upon measures of averaged evoked potentials (AEP) and power spectra (PS) to demonstrate hemispheric differences. The nature of the tasks appropriate to each of these methods of signal analysis generally require different cognitive activities and suggest different assumptions about cerebral specialization. This study investigated whether the tasks associated with either method were more likely to produce EEG asymmetries. Eighteen right-handed subjects participated in a three phase experiment which varied the amount of subject involvement in task performance. Phase I entailed passive listening to speech and nonspeech sounds. Phase II required active attention to speech and nonspeech sounds. Phase III involved a verbal matching task, a spatial rotations task, and a noncognitive control task. Auditory AEPs were measured in Phases I and II, and PS were measured in Phase II and III. EEG recordings were obtained from frontal and parietal areas of both hemispheres (F3, F4, P3, P4) referred to linked ears. Power spectra were derived from the 4-8, 8-13, and 13-20 Hz frequency bands at each lead. Despite statistically significant task and/or stimuli differences found in all three phases of study, essentially no task by lead interactions were obtained. That is, interhemispheric activity did not covary with differing stimuli and tasks. The absence of such interactions calls into question uncritical acceptance of a simple direct relation between task performance, EEG activity, and hemisphere specialization.

Relationship between EEG amplitude and subjective rating of task strain during performance of a calculating task

With the use of a calculating work tester, a paced calculating task consisting of addition or subtraction of two 2-digit numbers was imposed for five minutes at each of eight grades of workload upon 24 healthy male students. The subject's scalp EEG was recorded for 10 s at the occipital midline (Oz) during rest and task performance, and the average amplitude was obtained for each of the five spectral bands. The subjective rating of the hardness of each task was adopted as a subjective measure of mental task strain. The logarithm of percentage of errors, the amplitudes of the alpha, beta 1, and beta 2 bands and the subjective ratings of hardness of the task increased in linear proportion to the workloads of the task. The highest correlation was found between the subjective ratings and the percentage increases of the Oz beta 2 amplitude over the resting level. It was suggested that these two measures would be useful for the measurement of mental task strain. In addition, it was judged that workloads of more than 90% of capacity induce excessive mental task strain in the subject.

Spectral analysis of electroencephalogram during perceptual-motor learning

Spectral analysis of the electroencephalogram was utilized to determine attention demands during learning of a perceptual motor task. Fifteen subjects participated in the task which consisted of 15 trials of the mirror star learning task. EEG was monitored bilaterally from the occipital and parietal lobes during each trial and analyzed for intensity and mean frequency components within five different bandwidths. All subjects rapidly improved performance in terms of both time and error reduction although the former measure appeared to be a better fit of the supradiagonal form of matrix typically found for this type of learning. Mean alpha frequency increased slightly during the task while delta frequency decreased.

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.

A cognitive-motor network demonstrated by positron emission tomography

The rate of local cerebral glucose metabolism was measured in subjects receiving a verbal (n = 4) and a spatial (n = 4) task. The verbal task produced greater metabolism in Wernicke's area relative to the right hemispheric homotopic region, whereas the spatial task produced greater metabolic activity in the right hemispheric homotopic region. Broca's area and its right hemisphere counterpart showed symmetrical activity during the verbal task, but there was a significant asymmetry to the right during the spatial task. Lateralized task effects were also obtained in the frontal eye fields, supporting a hypothesized neural network linking cognitive activity with motor orientation.

Asymmetrical brain activity discriminates between positive and negative affective stimuli in human infants

Ten-month-old infants viewed videotape segments of an actress spontaneously generating a happy or sad facial expression. Brain activity was recorded from the left and right frontal and parietal scalp regions. In two studies, infants showed greater activation of the left frontal than of the right frontal area in response to the happy segments. Parietal asymmetry failed to discriminate between the conditions. Differential lateralization of the hemispheres for affective processes seems to be established by 10 months of age.

Induced coding strategies and hemispheric differences in matching letter pairs

The importance of task requirements in producing visual half-field asymmetries was investigated through manipulation of the criteria by which a central probe and a unilateral target letter were matched. Physical characteristics of the letters were emphasized (those made up of straight lines only vs those having at least one curved feature, e.g. F vs P). An interaction of visual field and type of judgment (match vs mismatch) was found for manual response time. Matching responses were faster to RVF than LVF probes and mismatches were faster to LVF than RVF probes. The significance of this interaction for models of hemispheric asymmetry is discussed.

Motor and cognitive interactions during lateralized cerebral functions in children: an EEG study

Power spectra of hemispheric EEG asymmetries were recorded in children performing cognitive tasks requiring motor output. Verbal and spatial cognitive tasks were administered and subjects performed tasks with either right or left hand. The average power in the alpha band was computed. Significant changes in right/left ratios were obtained when the task changed from verbal to spatial. A major predictor of which hemisphere was most activated, however, was the hand involved in solving the task. It appears that attention must be directed to both the cognitive and motor components when investigating asymmetries of cerebral hemisphere function.

The effects of bilateral EEG biofeedback on verbal, visual-spatial, and creative skills in learning disabled male adolescents

Twenty-four learning disabled adolescent boys with verbal IQ deficiencies were pretested on measures of convergent and creative thinking, assigned to eight weekly, 21-minute sessions of one of two bilateral EEG biofeedback training conditions or a no-training control condition, and post-tested two months after the pretest. The EEG biofeedback training produced baseline effects in the presumably dysfunctional left hemisphere and had an impact on arousal in-task, suggesting remedial potential for the possible hemispheric arousal deficits in learning disabilities. Training the right hemisphere toward higher arousal and the left hemisphere toward lower arousal resulted in a notable improvement in arithmetic.

Hemispheric quantitative EEG changes following emotional reactions in neurotic patients

Twenty-four right-handed patients undergoing primal therapy served as subjects in the study. They all showed symptoms of tension, anxiety, and/or depression. The patients' right and left temporal EEGs were recorded immediately before and after a therapy session. Recordings were done while the patients were resting, and while they were performing a verbal and a visual task with their eyes closed. The EEG data were analysed off-line with a computer, using quantitative amplitude analysis in the 1.5 to 30 Hz frequency band. A "high intensity" group (n = 13) having high ratings of emotional activity in their therapy session was compared with a "low intensity" group (n = 11) with low ratings. The results showed that only in the "high intensity" group was there a significant increase in mean amplitude and amplitude variance in the right hemisphere, measured across conditions. A between-group comparison revealed that the "high intensity" group showed a significantly larger increase in right hemisphere variance and in right over left variance ratio, relative to the "low intensity" group, in which these variables were almost unchanged. These results indicate a greater involvement of the right hemisphere in emotional activity. It is also suggested that the EEG changes found in the "high intensity" group, following a therapy session, reflect a general deactivation of the brain and a functional improvement of the right hemisphere.

Some quantitative hemispheric EEG measures reflecting the affective profile of students differing in university academic success

Quantitative measurements of the integrated epoch based EEG amplitudes obtained from two groups of university students differing in academic success during an eyes close, relaxed state revealed significantly higher right/left amplitude variance ratios and more right hemispheric non-Gaussian cumulated amplitude distributions among unsuccessful students. These data, which resemble patterns often found in depression, are consistent with, and appear to reflect specific affective differences that emerge using a concurrently administered, conventional psychometric inventory (Beck Depression Inventory) as well as a subjective self-assessment questionnaire. The results of this study may be useful in further elaborating the nature in which right hemispheric brain processes serve to mediate affective behavior, as well as influence academic performance.

Cortical power spectrum analysis of hypnotic pain control in surgery

Cortical power spectrum (CPS) of brain potentials was recorded from the scalp between prefrontal and parietal regions in both right hemisphere (RH) and left hemisphere (LH). A pattern of laterality shift in CPS occurred at different stages during an extensive oral surgery, performed under hypnosis, in a young female patient. Video and audio recordings as well as psychophysiological recordings were obtained through the following 6 stages: Baseline, Hypnosis, Surgery (1 hr, no cortical recording), Immediate Postsurgery Procedure, Hypnotic Re-experience, Hypnotic Rest, and Posthypnotic Baseline. Indications of anxiety and pain scores were reported in writing by the patient through verbal command by the hypnotist. In each stage, 10 min of CPS (10 spectrum/stage, 8 epochs/spectrum, 6 seconds/epoch) were analyzed by a PDP-11 computer. The results of CPS analysis demonstrated significant large total power reduction at different stages. There was significant correlation between both hemispheres at baseline, but dissociation of hemispheric power output occurred during hypnosis stages. LH was more dominant than RH during baseline and presurgery hypnosis, but both were leveled-off immediately following the surgery procedure. However, RH became more dominant during all postsurgery hypnosis stages. Interestingly, this pattern shifted back to the original relationship during the posthypnotic baseline stage. Specific changes of spectral power in theta and alpha of EEG activities in both hemispheres also occurred in conjunction with hypnosis.

Lateralized differences associated with semantically varied auditory material

EEGs were recorded from 13 subjects while they listened to four tape-recorded passages differing in semantic content. The distribution of alpha band power over the two hemispheres, measured at T3/T4, was found to show significant task-dependent shifts. More reality-oriented passages tended to be processed with greater left-hemisphere involvement, while "pleasurable" material showed significant right-hemisphere involvement. Since the differences in laterality were not related to grammatical measures of linguistic complexity, the apparent shifts were attributed to semantic differences between the tasks. Explanation of the results is made in terms of a theory of the metacontrol of cerebral processing.

Cerebral lateralization: relation to subject's sex

Patterns of reflective LEM's have been correlated to a number of cognitive and personality variables, bu the relationship to sex, education, and mental illness is unclear. In this study females produced significantly more R-LEM overall indicating a preferential use of left hemisphere mechanisms when they initiate reflective thought. Females also produced more R-LEM for verbal nonemotional material, suggesting stronger lateralization of language abilities to their left hemisphere. Emotional and spatial stimuli were less well lateralized to the right hemisphere in females, and education was an unimportant variable for both sexes. Schizophrenia was independently associated with increases in total R-LEM indicating increased left hemisphere activity in this group.

Electroencephalographic analysis: a methodology for evaluating psychotherapeutic process

The relationship between individual differences in listening style and clinical sensitivity was studied. Listening style is conceptualized as extending from a critical, analytic, focused attitude to a holistic, intuitive, free-floating attitude. We studied the listening styles of psychiatric residents while they listened to a tape recording, a 17-minute fragment of a psychotherapy that had been rated by a panel of experts as containing 22 cues reflecting the patient's concern with termination of treatment. The ability of clinicians to identify these cues is our experimental measure of clinical sensitivity. Our measures of listening style include eyeblink rate, memory for high-imagery words, and electroencephalogram recorded from electrodes over the right and left temporal areas, all measured while psychiatric residents listened to the tape. Results suggested that an abundance of alpha indicates a readiness on the part of the listener to process clinically relevant information. In addition, a listening style with engagement of the right hemisphere predicted clinical sensitivity. These findings suggest ways to study how the skilled clinician "tunes" himself empathically to his patient.

Biofeedback-regulated asymmetries in facial skin temperature

Although 5 of 7 subjects regulated asymmetries in skin temperature, differences between right and left temperatures were small. No relationship between hemisphere-specialized cognitions and asymmetries in facial skin temperature was demonstrated.

EEG patterns during 'cognitive' tasks. II. Analysis of controlled tasks

This experiment was designed to distinguish possible EEG correlates of the cognitive components of tasks from EEG patterns associated with stimulus characteristics, limb and eye movements, and performance-related factors such as subjects' ability and effort. Thirty-two right-handed adults each performed 30 trials, lasting 6-15 sec each, of four simplified, controlled tasks: mental rotation of geometric forms, serial addition of a column of signed digits, substitution of letters with subsequent word recognition and visual fixation. The first three tasks could not be differentiated from each other. Each of these tasks could be differentiated from visual fixation by approximately 10% generalized reductions in alpha and beta band intensities, and slight increases in theta band intensities frontally and occipitally. We conclude that the EEG patterns which differentiated the complex tasks described in Part I were due to inter-task differences in stimulus characteristics, efferent activities and/or performance-related factors, rather than to cognitive differences. With these controls, no evidence for lateralization of different types of cognitive activity was found in the EEG.

EEG patterns during 'cognitive' tasks. I. Methodology and analysis of complex behaviors

This paper presents a methodology which uses nonlinear pattern recognition to study the spatial distribution of EEG patterns accompanying higher cortical functions. The multivariate decision rules reveal the essential EEG patterns which differentiate performance of two tasks. Cross-validation classification accuracy measures the generality of the findings. Using this method, EEG patterns were derived from a group of 23 adults during performance of several complex tasks, including Koh's block design, writing sentences, mental paper folding, and reading silently. These patterns discriminate between the tasks, are consistent with, and extend the results of, visual EEG interpretations and univariate analysis of spectral intensities. Since writing sentences could not be distinguished from mere scribbling, it is unclear whether the EEG patterns found to distinguish complex behaviors were related to the cognitive components of tasks, or to sensory-motor and performance-related factors.

EEG and autonomic responding to verbal, spatial and emotionally arousing tasks: differences among adults, adolescents and inhalant abusers

The present study investigated the physiological responses of an adolescent inhalant abuse group, an adolescent non-abuse group, and an adult non-abuse group elicited by three types of tasks: verbal, spatial, and emotionally arousing. Each group consisted of 10 male Mexican-American subjects. Bilateral EEG and electrodermal activity, as well as heart rate, were monitored. While exploring for possible heart rate and hemispheric alpha wave differences in response to predominantly verbal and spatial tasks, an attempt was also made to discover if electrodermal responses could be bilaterally differentiated. Another purpose of the study was to explore possible psychophysiological differences between a younger and older group, and between an inhalant abusing group and a non-abuse group, in response to the three types of tasks. Results indicated that attempts to produce task-related EEG hemispheric asymmetry were largely nonsuccessful. Bilateral electrodermal responses were also not greatly differentiated. It was suggested that stronger task manipulations were needed. Significant group differences were found for initial physiological response levels (adults demonstrated higher levels than the two adolescent groups) and for heart rate response to the emotionally arousing task (non-abusing subjects demonstrated greater heart rate acceleration than inhalant abusing subjects). It was suggested that group differences in initial levels occurred due to the adult groups's greater involvement in the experimental situation. Heart rate differences to the emotionally arousing situation were discussed in terms of Zuckerman's sensation seeking hypothesis.

EEG asymmetries in recognition of faces: comparison with a tachistoscopic technique

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 FEG 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.

Cerebral specialization, writing posture, and motor control of writing in left-handers

It has been suggested that the inverted hand position of left-handers during writing indicates the left hemisphere of their brain is linguistically specialized and that the writing of these left-handers may be controlled via ipsilateral pathways. Electroencephalograph alpha asymmetry measures at central and parietal leads, as well as dichotic tests, differentiated right-handers from left-handers, but not inverters from noninverters. Electroencephalograph differences between hand posture groups did appear, but only at occipital leads during reading and writing tasks. Regardless of hand posture or speech lateralization, the right central region of the brain is significantly involved in the control of left-handed writing.

Visual-field asymmetries in letter recognition: evidence for asymmetry in early visual registration

Two experiments on visual-field differences in tachistoscopic letter recognition are described. In the first, a bright pre-exposure field with a black fixation point was used, and the conventionally expected dominance of the right visual field was found. However, a large number of "blank" trials were observed, in which subjects completely failed to detect the presence of the flashed target. These "blanks" were themselves significantly asymmetric between visual fields, suggesting that asymmetry in early stimulus registration may play an unsuspected role in typical measures of cerebral asymmetry in recognition accuracy. This was confirmed in a second experiment in which use of dark pre-exposure fields eliminated "blanks" and led to higher over-all accuracy, with no visual-field differences. Implications for interpretation of laterality data with normal subjects are discussed.

Successful and unsuccessful university students: quantitative hemispheric EEG differences

Quantitative measurements of EEG amplitudes were obtained on academically successful and unsuccessful university students during a 5 min, eyes closed, relaxed state. Integrations measured continuously the fully rectified amplitudes of brain waves cumulated over successive epochs of 5 s, regardless of the correlation of a wave to a particular frequency band. The poor academic students, as a group, displayed a significantly higher right/left variance ratio of the cumulated amplitudes at both the temporal and occipital sites than the academically successful group. Upon examining the histograms for these cumulated amplitudes, it was found that the unsuccessful students displayed a greater number of polymodal (non-Gaussian) distributions, particularly in the right hemisphere. These data, which resemble patterns often found in depression, suggest a relative disorganization of right hemispheric activity in the unsuccessful students, and within limits, seems related to the cognitive and/or emotional stability of these students.