| Abstract: | Mechanisms of the "enhancing" evoked potential arising in the visual cortex in response to repeated stimulation at intervals of 100–150 msec were investigated on unanesthetized rabbits. Such intervals correspond to the phase of postinhibitory activation caused by the first (conditioning) stimulus. It is shown that the enhancing response lasts slightly longer than the primary response to a single stimulus and develops upon stimulation of the optic nerve and subcortical white substance under the point of derivation. The enhancing response is accompanied by a high-amplitude excitatory postsynaptic potential in cortical neurons and by a burst of impulse activity. Hence it can be concluded that it is generated by excitatory synapses of cortical neurons. Characteristic features of the enhancing response are the relation between the duration of the response and its amplitude (the response is shorter, the higher its amplitude) and the weak effect of the intensity of the stimulus on the amplitude of the response. An analysis of the possible mechanisms of enhancement of the response when the stimulus evoking it coincides with the phase of postinhibitory activation leads to the suggestion that this response is generated by a recurrent excitatory intracortical system. This suggestion makes it possible to explain the ability of the response to be enhanced in the presence of postinhibitory activity and some other properties of it.A. N. Severtsov Institute of Evolutionary Animal Morphology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 64–72, January–February, 1970. |
