Harmonic composition and topographic distribution of responses to sine wave modulated light (SML), their reproducibility and their interhemispheric relationship.

1. Responses to sine wave modulated light (SML) were recorded bipolarly from the occipital, parietal and temporal scalp areas on the right and the left sides of 9 normal individuals. Their harmonic composition was determined by means of Fourier analysis. 2. The wave form of the responses was rather complex in relation to the stimulus and differed according to stimulation frequency and localization. 3. The components of the responses were principally the 1st and 2nd harmonics. 4. The amplitudes of the harmonics were usually largest over the occipital and smallest over the parietal scalp areas. 5. Considerable intra-individual amplitude variabilities of both harmonic component amplitudes existed in all areas of all individuals. 6. The interhemispheric amplitude correlations of 1st and 2nd harmonic components, simultaneously recorded in homologous occipital, parietal and temporal areas, were measured by means of Kendall's rank correlation test. 7. The interhemispheric synchrony of the harmonic components was measured by determining the phase differences between each of the response components in homologous right and left scalp areas. 2. In subjects with a high amplitude correlation a strong synchrony existed and vice versa. 9. It is suggested that the interhemispheric relationships between harmonic components of the responses to SML might be of importance for clinical application. This opinion is supported by the fact that through SML evoked responses a considerable data reduction is obtained in comparison with the responses to light flashes.