Efferent fibers in the frog optic nerve

Abstract

Activity was recorded extracellularly from units in the retina and optic nerve of curarized frogs. The objectives were, firts, to seek and characterize changes in unit receptive field properties resulting from experimentally induced changes in efferent influence on the retina; and, second, to identify efferent units in the nerve itself. Where necessary, statistical techniques were used. “Off” and “on-off” afferent units exhibited changes in both spontaneous and visual-stimulus produced activity, in association with auditory or cutaneous stimulation. Changes in receptive field size and organization were also associated with extravisual stimulation. The activity of efferent units in the proximal part of the cut optic nerve was observed and recorded, displaying in some cases changes such as adaptation and off responses, in association with extravisual stimulation. The results suggest a link between a class of efferent responses to extravisual stimuli and the sensitivity of retinal units; more specifically, the authors have concluded that efferent activity influences an inhibitory component in the retina common to three of the known functionally classified types of visual afferent fibers. The link between efferent fibers and ganglion cells is postulated to be the processes of amacrine cells.