INFLUENCES OF HORIZONTAL CONNECTIONS ON VISUAL RESPONSES IN RABBIT STRIATE CORTEX

The goal of this study was to examine the role of horizontal connectio ns in rabbit striate neurons. Anaesthetized rabbits were prepared in t he usual fashion for single-cell recordings in area 17 of the visual c ortex. We compared responses evoked by moving and stationary stimuli p rior to, during and after recovery from lateral microinjection of eith er lidocaine (n = 61), gamma-aminobutyric acid (GABA, n = 18) or bicuc ulline (n = 8) 2 mm from the recording site. This procedure allows eva luation of the contribution of neighbouring neurons in visual response s. Results showed that striate neurons are dependent on the adjacent c ells' excitability. Modification of responses to stationary targets su ggests that lateral interactions play a role in the generation of disc harges to fixed stimuli. Lateral inactivation preferentially influence d non-directional over direction-selective units. This influence usual ly resulted in the non-directional neuron becoming directional by atte nuation of the visually driven response in one direction. Simple and c omplex cells tended to be influenced differently by lateral inactivati on. Simple cells became less responsive, whereas complex cells became more responsive. This dichotomy among cellular types suggests that sim ple cells receive mainly excitatory horizontal influences, while compl ex cells are contacted mostly by lateral inhibitory inputs.