Electrophysiology of the intertectal commissures in the pigeon. II. Inhibitory interaction.

Abstract

1. In pigeons with one retina chronically removed, the tectal response to the stimulation of the contralateral eye was subjected to conditioning stimulation applied to the opposite tectum. The effect on evoked potentials and unitary responses was studied. 2. The response evoked by light flashes was depressed by the conditioning stimulation. In the response evoked by electrical stimulation of the optic nerve, the negative component of the slow wave was depressed by the conditioning stimulation. This depression was abolished by section of the tectal and posterior commissures. 3. Among 222 units activated by optic nerve stimulation, the conditioning tectal stimulation suppressed, delayed or reduced the discharge of 49 units (22%). The tectal stimulation did not evoke unitary discharge by itself nor had a facilitatory effect. The time course of the inhibition was from 5–70 msec with a maximal effect at 20–30 msec. The inhibited units had a latency longer than 4 msec and did not follow a stimulation frequency higher than I/sec. No unit could be inhibited in the superficial layers of the tectum, where the evoked response is negative, but 25% of the units were inhibited in the middle and deep layers, where the response is positive-negative or positive.