Unit analysis of the pretectal nuclear group in the rat

Abstract

Unit responses to visual stimuli in the pretectal region of the rat were investigated with steel microelectrodes. Most units could be classified into two broad categories; “phasic” (brief on and off discharges) and “tonic‐on” (sustained discharge during the visual stimulus). The responsive region appears to be coextensive with the n. praetectalis anterior (Pta) which can be divided into a dorsal portion containing “phasic” units and a ventral portion containing “tonic‐on” units. The projection of the contralateral visual field is a mirror reversal of the field projection onto the superior colliculus. “Tonic‐on” units may suserve total luminous flux detection necessary for the pupillary reflex. The topographical organization of units within Pta, as well as their diverse properties may account for residual visual function in animals with extensive lesions of the main visual pathways.