GABA inactivation of area V4 changes receptive-field properties of V2 neurons in Cebus monkeys

To investigate the contribution of feedback circuits from area V4 to the receptive-field properties of V2 neurons, we used tungsten microelectrodes to record extracellular single units in these visual areas, before and after pressure injections of a solution of 0.25 mol/L of GABA in two anesthetized and paralyzed Cebus apella monkeys. The visual stimulus consisted of a single bar moving in one of eight directions. Using a device made of four stainless steel pipettes and one central tungsten electrode, we inactivated, with different amounts of GABA, topographically corresponding areas of V4, while studying V2 neurons. We studied a total of 36 V2 neurons during six sessions of GABA injections into area V4. GABA inactivation of visual area V4 produced a general decrease in the excitability of the neurons, which included a decrease in spontaneous and driven activities, followed by changes in direction selectivity. The changes in selectivity were toward an increase in directional selectivity and decrease in orientation selectivity. Thus, feedback connections arising from V4, an area of the ventral steams of visual information processing, are capable of not only modulating the spontaneous and driven activity of V2 neurons, but also of modifying V2 receptive field properties, such as its direction and/or orientation selectivity.