Lateral specialization of cognitive mode: II. EEG frequency analysis

Electroencephalogram correlates of higher cortical functions

By means of two-stage, nonlinear multivariate pattern recognition, electroencephalograms (EEG's) were analyzed during performance of verbal and spatial tasks. Complex scalp distributions of theta-, beta-, and, to a lesser extent, alpha-band spectral intensities discriminated between the two members of a pair of tasks, such as writing sentences and Koh's block design. Small EEG asymmetries were probably attributable to limb movements and other uncontrolled noncognitive aspects of tasks. Significant EEG differences beteeen cognitive tasks were eliminated when controls for inter-task differences in efferent activity, stimulus characteristics, and performance-related factors were introduced. Each controlled task was associated with an approximately 10 percent reduction, as compared with visual fixation, in the magnitude of alpha- and beta-band spectral intensity. This effect occurred bilaterally and was approximately the same over occipital, parietal, and central regions, with some minor difference over the frontal region in the beta band. With these controls, no evidence for lateralization of different cognitive functions was found in the EEG.

Choice of handedness measures in studies of hemispheric specialization

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

The EEG, brain function, and Thomson's sampling theory

If the EEG is regarded as a measure of functional organisation in the brain, it may yet be possible to use it as an independent variable in psychological studies. The method of Maxwell et al. (1974) suggest how this relationship may be quantified. These authors develop the hypothesis that EEG power is proportional to p, the number of brain components involved in cognition. However, evidence is reviewed here to suggest an alternative hypothesis for the case of EEG alpha activity, namely that power is proportional to (1--p).

The effect of transcendental meditation on right hemispheric functioning

This study reports two experiments investigating the effects of transcendental meditation on right hemispheric functioning. The task used in both experiments was the Seashore Tonal Memory Test. In the first experiment a non-meditator group and an experienced meditator group were run. The design involved three periods: a pretest, a meditation or rest period, and then a posttest. The results showed the experienced meditators were significantly better in both pretest and posttest performance. There were no pretest-posttest differences. The second experiment was done to replicate the first experiment and to control for possible selection bias. The design was the same as the first experiment, except that an additional group of inexperienced meditators was included. The results again showed significantly superior performance for the experienced meditators compared to the non-meditators. In addition, the experienced meditators were superior to the inexperienced meditators. There were no significant differences between the non-meditators and the inexperienced meditators. These results support the hypothesis that meditation facilitates right hemispheric functioning. Alternative explanations, such as selection bias, are also discussed.

Lateral specialization and psychiatric issues: speculations on development and the evolution of consciousness

At the start of this lecture, I invited you to indulge with me in a "dessert" of speculations. I hope it has been a sufficiency, not a surfeit. In summary, we have examined a hypothetical model of some dissociations of consciousness and the expression of unconscious symptoms in adults; we then explored some possible conditions that would account for the development of separate mental streams. In the course of this exploration we were led to question some basic assumptions about the unity of the self, and we proposed some possible mechanisms by which lateral specialization develops in children. This model of the development of lateral specialization has some implications for the study of evolution of the human brain and consciousness. It would seem useful to examine the relationship between the evolution of the commissural systems and the evolution of different capacities for consciousness. According to this model, the full development of lateral specialization depends upon the later myelination of the commissures, which makes possible the autonomy and competition between hemispheres. By this means, only minimal differences between hemispheres need to be specified genetically, since the rest of lateralization can be produced by progressive differentiation, through interactions with the environment. Thus man's eternal, internal struggle may be the price paid for the evolution of lateral specialization.

Auditory evoked potentials as probes of hemispheric differences in cognitive processing

The amplitude of auditory evoked potentials recorded from the cerebral hemispheres to pairs of task-irrelevant tones was related to differential hemispheric engagement in ongoing cognitive activity (for example, verbal versus musical). The hemisphere hypothesized to be most engaged in the ongoing cognitive task, as compared to the unengaged hemisphere, produced a greater potential difference between the temporal and reference electrode to the second of the tone pairs. These findings are related to "fast habituation" and "recovery cycle.".

Self-regulation of hemispheric asymmetry

This study was performed to determine if individuals could demonstrate self-regulation of average EEG power of one hemisphere in comparison to the other. Temporal EEG was recorded from 8 males and 6 females. After a practice session, the subjects were instructed to increase or decrease the practice session, the subjects were instructed to increase or decrease the ratio of left to right temporal EEG. The subjects were given on-line feedback in the form of a graph presented via a computer display screen. The study demonstrated a significant ability of the subjects to change differentially the hemispheric power ratios upon instruction.

Hemispheric specialization of language: an EEG study of bilingual Hopi indian children

Electroencephalographic (EEG) recordings were obtained from electrode placements over the left and right frontal and parietal lobes of the brain in sixteen Hopi Indian children listening to tape recorded children's stories in the Hopi and English languages. Spectral analysis of the EEG data revealed that, for the parietal leads, alpha desynchronization was relatively greater over the right hemisphere for listening to Hopi than for listening to English, which indicates a greater right hemisphere participation in the processing of the Hopi speech. The results of the experiment are directionally consistent with our hypothesis, and imply that linguistic relativity may exist on a neurolinguistic level, such that languages can differ in the relative degree to which they serve as instruments of thought in a propositional, left hemisphere mode, or in an appositional, right hemisphere mode.

Electroencephalographic and reaction time asymmetries to musical chord stimuli

EEG was recorded over left and right hemispheres at temporal leads (T3, T4) referred to the vertex (Cz) in 16 right-handed male subjects. Musical chords were presented randomly in monaural sequence, during a task which required a selective motor response to stimuli presented to one ear. The integrated amplitude of the 8-13 Hz alpha rhythm was measured when subjects listened passively. Under all conditions, a lower mean alpha amplitude was recorded over the right hemisphere than the left, regardless of which ear was stimulated. Alpha suppression over the right temporal area was accentuated when the performance task directed attention to the stimulus. Reaction time to left ear stimulation was shorter than that for the right ear. With monaural stimulus presentation behavioral asymmetry, and various EEG asymmetries can be observed. There is hemispheric asymmetry associated with attention to task relevant stimuli indicated by reduction in the alpha rhythm over the right temporal area and asymmetry in reaction time with greater efficiency of the left ear to muscial chords.

Bilateral EEG differentiation of stimuli

The EEG of both right and left hemispheres was monitored while subjects were presented with words, music, arithmetical problems and abstract pictures, (15 trials of each treatment, 9 sec per trial). The left side of the brain was most activated during presentation of words and arithmetic, whilst the right side of the brain was most activated during presentation of music. In addition, the right side was more activated during exposure to arithmetic than to words. The pictures were not differentiated by either side of the brain and it is possible that they had the effect of deactivating or relaxing subjects, since they yielded high abundance values compared with other stimuli. This study confirms earlier findings showing significant between-hemisphere ratios for arithmetic and words. In addition, however, the within-hemisphere analyses show that music affects the right hemisphere (without inducing between-hemisphere changes) and that arithmetic also activates the right hemisphere if compared with the non-activating effects of words.

Sex differences in patterns of EEG asymmetry

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

Right hemisphere lateralization for emotion in the human brain: interactions with cognition

Right-handed subjects tend to look to the left when answering affective questions. The relative shift in gaze from right to left is accentuated when the questions also involve spatial manipulation and attenuated when the questions require verbal manipulation. The data support the hypothesis that the right hemisphere has a special role in emotion in the intact brain, and that predictable patterning of hemispheric activity can occur when specific combinations of cognitive and affective processes interact.