[Topography and reactivity of the visual evoked potential]

Augmenting/reducing (A/R) of visual evoked potentials (VEP) has been repeatedly observed in central derivations, with some subjects increasing, and others decreasing, VEP amplitude with increasing intensity of stimulation. Central derivations also exhibit hemispheric lateralization regarding A/R. This paper explores central and occipital VEP in the same population of 16 healthy, right-handed male subjects, stimulated with binocular light flashes 10 usec in duration delivered by à Grass PS2 stimulator at a rate of 1/sec and at the intensities of 0.36, 0.72 and 1.44 joules at source. Amplitudes and latencies of components P1, N1 and P2 agreed with those reported in the literature. On the basis of amplitude/intensity slope functions of "peak to peak" amplitudes (P1N1 and NIP2) at Cz, 10 augmenters (slope greater than 0) and 6 reducers (slope smaller than 0) were found. Compared to central leads (C3 and C4) occipital ones (O1 and O2) did not exhibit significant interhemispheric differences. Vertex augmenters for N1P2 were occipital reducers and vice-versa. The different characteristics of A/R at occipital and central leads are interpreted in terms of stages of visual information processing in primary and association areas and functional significance of VEP components.