The relationship of visual evoked potentials to cortical physiology.

The last 15 years have seen a rapid expansion in studies on human visual evoked potentials (VEP), both a t the fundamental and at the clinical level. A wide variety of stimulus conditions have been explored,’ new types of mathematical tools have been i n t r o d ~ c e d , ~ . ~ and there has been an increasing appreciation of possible VEP correlates with underlying physiological mechanisms! Variability of the folding and size of the human striate cortex’ as well as the remote location of human scalp electrodes, however, limits the accurate localization of human VEP components to particular cortical structures. In this regard it would seem desirable to explore the VEP of a laboratory animal closely related to the human. In this paper I discuss two approaches that may prove both useful and complementary in deciphering visual evoked potentials in monkey, and by extrapolation, in man. The first approach involves the use of fine stimulus control, noting the degree to which the VEP amplitude varies with small changes in stimulus characteristics. The second approach, still in the preliminary stages, involves the use of current source density analysis, a method to localize the generating processes of the VEP to specific cortical laminae and sublaminae.