CORTICAL AND RETINAL RESPONSES TO COLORED LIGHT FLASH IN ANESTHETIZED CAT

Abstract

Cortical (primary optic cortex) and retinal responses to light flash were recorded simultaneously and compared with respect to wave form, amplitude and latency characteristics in the anesthetized cat. The light flash was variable with respect to color (blue, 445 m[mu].; green 560 m[mu].; yellow 575 m[mu].; and red 620 m[mu].) and intensity (5 decades). Threshold of the cortical response lay about a decade below the retinal threshold. The shape of the "on" response of the cortical potential consisted of 2 phases, a surface-positive followed by a surface-negative phase. At low and moderate intensities, there was a double positive response. At higher intensities, the initial phases were superimposed with 4 or 5 spikes. With increasing intensity, the amplitude of both cortical and retinal responses increased and the latency decreased. Color of the stimulating light affected shape, amplitude and latency of the cortical response. The 2 components of the positive response were most pronounced in response to yellow and red. Amplitude of the cortical response to blue was greater than to green stimulus when the intensity of the stimuli was such as to evoke retinal responses of equal amplitude. Latency of the cortical response to a blue was longer than to a green, yellow or red stimulus when the intensity of the stimuli was such as to evoke retinal responses of equal latency. Differences in cortical responses to colors could not be solely attributed to peripheral events.