Intraretinal slow potentials evoked by brain stimulation in the primate.

Abstract

In monkeys under nembutal anesthesia, stimulation of the optic nerve evokes a long latency positive slow potential, the P-wave, in the retina. The P-wave is distinguished from antidromic discharge of ganglion cells by its longer latency greater susceptibility to barbiturate and hypoxia its location within the retina. In this study: The fibers concerned with the initiation of the P-wave were found widespread throughout the dorsal half of the optic tract and lateral geniculate body, but in no other brain structure. The maximum amplitude of the P-wave was identified with the inner plexiform layer by an electrode marking technique. P-waves evoked by tetanic stimulation became fused at high stimulus frequencies. Under these conditions a sustained positivity was recorded from the inner plexiform layer. These findings support the suggestion that the P-wave is a post-synaptic retinal potential, but do not support the previous hypothesis that efferent fibers of the optic nerve are involved in its pathway. An alternative hypothesis based on recent electron microscopic observations of the monkey inner plexiform layer is presented.