Distinct Feedforward and Feedback Effects of Microstimulation in Visual Cortex Reveal Neural Mechanisms of Texture Segregation

The visual cortex is hierarchically organized, with low-level areas coding for simple features and higher areas for complex ones. Feedforward and feedback connections propagate information between areas in opposite directions, but their functional roles are only partially understood. We used electrical microstimulation to perturb the propagation of neuronal activity between areas V1 and V4 in monkeys performing a texture-segregation task. In both areas, microstimulation locally caused a brief phase of excitation, followed by inhibition. Both these effects propagated faithfully in the feedforward direction from V1 to V4. Stimulation of V4, however, caused little V1 excitation, but it did yield a delayed suppression during the late phase of visually driven activity. This suppression was pronounced for the V1 figure representation and weaker for background representations. Our results reveal functional differences between feedforward and feedback processing in texture segregation and suggest a specific modulating role for feedback connections in perceptual organization. •Microstimulation of visual cortex evokes local excitation followed by inhibition•Microstimulation of V1 causes feedforward excitation and inhibition in V4•Microstimulation of V4 only causes feedback-based reductions in V1 firing rates•When V4 is suppressed by microstimulation, V1 figure-ground segregation is reduced Klink et al. probe interactions between visual cortical areas V1 and V4 with electrical microstimulation. Microstimulation effects reliably propagated in the feedforward direction. In the feedback direction, they depended on visual stimulation and figure-ground segregation. These results reveal the driving and modulatory roles of feedforward and feedback connections, respectively.