Diurnal periodicity of lateral asymmetries of the visual evoked potential in healthy volunteers.

Visual evoked potential (VEP) was analyzed in 24 healthy male volunteers (age: 25-35 years) between 7.00 a.m. and 4.00 p.m. to evaluate possible diurnal variation in hemispheric differences of the response to a diffuse or 1 degree flash and checkerboard pattern-reversal (stimulation: binocular). VEP was recorded over O1-A1 and O2-A2, and 64 exposures were averaged during each session. After diffuse and 1 degree flash stimulation the amplitudes of early components (latencies less than 140 ms) were higher over the right hemisphere (O2-A2) than over the left (O1-A1) in the morning. These differences disappeared during the afternoon. Late components (latencies greater than 250 ms) exhibited higher amplitudes over the left than over the right hemisphere during the whole experiment. With checkerboard pattern-reversal stimulation such a time-dependent change in the amplitudes of VEP between both hemispheres was not measurable.