Visual input to small-field and wide-field neurons in the postcruciate cortex of domestic cats

Abstract

Extracellular recordings were made of single neurons in the contralateral forepaw focus of the lateral postcruciate gyrus (field 4γ of sensorimotor cortex) of chloralose-anesthetized cats. Neurons were classified according to their suprathreshold responses and their subthreshold effects to electrical stimulation of the four paws and to flashes of the light. Two-thirds of all neurons sampled were excited by light flashes. Moreover, 94% of m neurons (neurons with large excitatory somatic receptive fields) but only 12% of apparent sa neurons (neurons with small excitatory somatic receptive fields) had excitatory visual input. Only five of 17 well-defined sa neurons, which had either inhibitory or no facilitatory input from the off-focus paws, had excitatory visual input. This is further evidence for a dichotomy between sa and m neurons, which are now known to differ in at least 18 properties. Neurons with excitatory visual input tended to be isolated deeper in the cortex. Some neurons had excitatory visual input but no apparent excitatory cutaneous input; those that were completely tested for cutaneous interactions were suppressed by all four paws.