Superior colliculus modulates oscillatory activity of neuronal responses in primary visual cortex

Abstract

The superior colliculus (SC) of mammals receives multisensory input and is supposed to play an important role in mediating spatial visual attention. Behavioral studies show that deactivation of cat SC results in a complete visual neglect of the contralateral hemifield, impairment of learning, and impairment of recognizing global visual features. The SC, via pulvinar complex, is the origin of ascending projections to the visual cortex. This pathway bypasses the lateral geniculate nucleus, and therefore supports a model of two parallel visual pathways. In this model the geniculocortical system performs a detailed analysis of stimulus features and the phylogenetically older extrageniculate pathway via SC participates in functions of spatial attention.

The goal of the present study was to reveal the influence of superior colliculus on information processing in primary visual. To this end, SC was unilaterally deactivated using cryoloops and neuronal activity in area 18 of anesthetized cats was monitored by optical imaging of intrinsic signals and electrophysiological recordings. Deactivation of the SC resulted in a decrease of response strength and led to a decrease in oscillatory activity in the gamma frequency range.

Gamma oscillations and the precise timing of neuronal discharges in the millisecond range are known to be involved in attention processes and learning tasks. Thus the observed impairment of these temporal aspects of neuronal activity in area 18 is likely to form a neuronal correlate of attentional deficits observed during deactivation of the superior colliculus in behavioral experiments.