CONE INDUCED INHIBITION OF ROD MEDIATED VISION ADDRESSED BY VISUAL EVOKED POTENCIAL (VEP)

The aim of the present work was to analyze the response of the human visual cortex by means of Visual Evoked Potentias, in order to test the lateral inhibition mediated by retinal horizontal cells. A total of 15 subjects underwent pVEP (pattern Visual Evoked Potential) electrophysiological tests designed by the members of the team. The protocols established by ISCEV standards for electrode placement were followed. Each subject was dark-adapted for 20 min prior to the start of the test, for adaptation to scotopic conditions. After adjusting visual acuity to the distance from the screen, ring-pattern stimuli of different sizes (2-5º from the fovea) were applied; in addition, foveal stimuli were also applied with different configurations: center-radial, center-black, center-red. The stimulation frequency was set at 1 Hz, averaging 150 responses for each ring/foveal stimulus combination. Power Lab device and LabChart software were used. A decrease in the amplitude of the N135 VEP wave evoked by the patterned rings was observed when the foveal region was stimulated with red light, compared with no foveal stimulation. Such a decrease was observed only for ring diameters corresponding to the axon length of horizontal retinal cells. Stimulation of the foveal region of the retina induces the inhibition of the light response mediated by rod stimulation in the perifovea. This phenomenon that can only be explained by the activity of horizontal retinal cells connecting cones with rods. This work demonstrates for the first time the inhibitory role of cones on rods through horizontal retinal cells.