Interhemispheric relationships of reponses to sine wave modulated light in normal subjects and patients.

(1) The interhemispheric amplitude correlations of the fundamental (A1) and second harmonic (A2) components of responses to sine wave modulated light were determined in the occipital, parietal and temporal scalp areas of a group of normal subjects and a group of patients with unilateral irritative EEG phenomena. The interhemispheric amplitude correlation was computed at 10- and 16-c/sec stimulation frequencies and under 3 conditions: no modulation and no attention (M-, A-), modulation 30%, and no attention (M+, A-) and modulation 30% and attention (M+, A+). The correlations wre expressed in the rank correlation coefficient of Kendall (rK). (2) Analysis of variance revealed that the interhemispheric amplitude correlation of A1 in the normal group was significantly larger than that in the patient group at a stimulation frequency of 10 c/sec and under the conditions (M-, A-) and (M+, A-). (3) Both groups presented the largest correlation coefficients in the occipital scalp area. (4) In the normal group a significant increase of rK occurred under the influence of modulation. Attention caused a decrease of the correlation coefficient of A1. In the group of patients this influence was not clear. (5) The standard deviation of the mean interhemispheric phase differences was considered as a measure of synchrony of the response components between the two hemispheres. The smallest values of standard deviation were found in the occipital scalp area of the normal group at 10 c/sec stimulation frequency. Considerable variations between individuals were observed in both groups. (6) The correlation between the interhemispheric amplitude correlation (rK) and the interhemispheric synchrony was influenced by changing modulation depth from 0 to 30% and by introduction of attention, mostly in the group of normal subjects. This phenomenon was considered to support the theory that in patients with unilateral EEG disturbances the interhemispheric relations are different from those in normal subjects. (7) The findings as to amplitude correlation (rK) were the same under the condition (M-, A-) as under the condition (M+, A-).