Mental activity and the e.e.g.: task and workload related effects

Validity of electrode placement at Fpz to detect alpha wave

The possibility on placing electrodes at Fpz-A2 instead of C3-A2 was investigated to obtain a more stable configuration avoiding obstruction by the hair. Our original system of alpha wave detection by a microcomputer was used, and a total of 22 all-night hypnograms of five healthy young students was recorded. Pearson's moment correlation coefficients of alpha wave % between the two positions were 0.780-0.948. Except for one subject, alpha wave % taken at Fpz-A2 tended to be 3-5% lower than that at C3-A2. The above analysis indicates that using EEG electrode position of Fpz-A2 is valid and useful as a stable electrode configuration for a long-time monitoring.

Quantitative EEG studies of pedophilia

Ninety six pedophiles, whose sexual orientation was confirmed by phallometric response to sexual stimuli, were investigated with quantitative EEG and compared to age- and sex-matched healthy controls. The EEG analysis showed a pattern of increased frontal delta, theta and alpha power (especially during verbal processing) and a pattern of reduced interhemispheric and increased intrahemispheric-interhemispheric coherence, right and left (only during verbal processing), an effect that was restricted to those who showed maximal erotic arousal for sexual partners aged 6-12 years. These findings will be discussed in the context of recent studies which suggest that sexual deviations in the male relate to altered dominant hemispheric functions with disruption of frontal interhemispheric relationships.

EEG coherence in unmedicated schizophrenic patients

We have recently shown that electroencephalogram (EEG) coherence data recorded with common reference methods, including those obtained from schizophrenics, are confounded by power and phase effects. Three published reports using bipolar recordings found that EEG coherence was higher in schizophrenics; however, only medicated patients were studied. To extend these findings, we measured EEG coherence from bipolar EEG recordings in unmedicated schizophrenics (n = 10), affective disorder patients (n = 8), and normal controls (n = 13) during resting and task conditions. Seven schizophrenics were restudied after a period of neuroleptic treatment. Schizophrenics had higher across-task interhemispheric (p less than 0.05) and intrahemispheric (p less than 0.04) coherence in the theta band and tended to have higher intrahemispheric alpha coherence (p less than 0.08). Medication treatment was associated with clinical improvement and increases in spectral power, but not with changes in coherence values. These results confirm those obtained by earlier investigations and suggest that increased coherence reflects the presence of anomalous cortical organization in schizophrenics rather than medication effects or transient states related to acute clinical disturbance.

Topographical distribution of absolute alpha-power in the EEG and psychopathology in schizophrenic outpatients

In 36 schizophrenic outpatients (Research Diagnostic Criteria) under neuroleptic maintenance treatment the EEG was recorded under resting conditions. The absolute alpha-power (7.5-13 Hz) was estimated by Fast Fourier Transform as the mean of 300 2-second epochs for the leads F3/A1, F4/A2, 01/A2 and 02/A2. Two lateralization quotients (anterior, posterior) and two anteriorization quotients (left, right) were calculated from the absolute alpha-power. Clinical status was assessed cross-sectionally with BRPS, GAS and CGI. The main findings are: 1) A linear relationship between the left/right ratio of absolute alpha-power over posterior regions and anxiety/depression--the more the alpha-power is left-lateralized, the higher the anxiety/depression score; 2) a curvilinear, inverted U-shaped relationship between the left/right ratio of absolute alpha-power over posterior regions and the score of schizophrenia-specific symptomatology; 3) the amount of daily neuroleptic dose (mgCPZ) has no impact on EEG-parameters. Results are discussed with respect to hemisphere asymmetry models of psychopathology.

The effect of brain function on coherence patterns in the bipolar EEG

Studies of the functional organization of the brain based on measurements of coherence in the EEG have, in the past, suffered from a methodological defect which has made interpretation of the results difficult. The effect involved is the use of an active common reference for the recording of the EEG. As a consequence, inferences related to the functional connectivity of brain between the non-referential sites using coherence have probably been wrong. To avoid the problem with the common reference, we have used bipolar derivations of the EEG and used measurements of coherence to reflect synchrony not between individual sites but between regions of the brain. The EEGs in a population of normal volunteers were examined with respect to coherence. Changes in the patterning of coherence were induced by utilizing EEGs from the volunteers during 3 different functional brain states. The first of these was the resting state, the second the verbal motor state and the third, the spatial motor state. The stepwise discriminant analysis method was used to study differences in the patterning of coherences in the 3 states. The results show that the spatial motor state was the most distinct in this regard amongst the 3 states. They results also interpreted as indicating that changes in the patterning of coherence from that in the resting state consisted of both functionally specific and functionally non-specific components.(ABSTRACT TRUNCATED AT 250 WORDS)

A critical review of EEG coherence studies of hemisphere function

Studies of hemisphere function involving the use of coherence analysis are reviewed. Despite the fact that many effects related to subject group and type of task have been reported, few seem to be reliable across studies. The assumptions which seem to underlie the use of coherence analysis are made explicit and discussed. Most investigators consider coherence levels to reflect certain 'baseline' patterns, possibly related to structural connectivity, upon which task and/or strategy effects may be superimposed. Use of a cephalic reference renders coherence effects virtually uninterpretable for a variety of reasons which are fully discussed.