The combination of feedforward and feedback processing accounts for contextual effects in visual cortex

Sensory systems must combine local features with context to infer meaning. Accordingly, context profoundly influences neural responses. We developed a unified circuit model demonstrating how feedforward and feedback inputs are integrated to produce three forms of contextual effects in mouse primary visual cortex (V1). First, reanalyzing existing data, we discovered that increasing stimulus size only weakly increases the area of V1 neural response, conflicting with previous models of surround suppression (SS). Second, through modeling, we found that, in Layer 2/3, (1) SS and its contrast dependence are largely inherited from Layer 4; (2) Inverse responses (IR) – size-tuned responses to a gray “hole” in a full-field grating – are driven by feedback connections provided they are sufficiently wide; (3) Cross-orientation surround facilitation is induced by the summation of feedback input driving IR with the feedforward-driven classical center response. The model accounts for many previous findings and makes multiple testable predictions. Highlights One model explains three different types of contextual modulation The widths of spatial response patterns grow much more slowly than stimulus size. Inverse responses depend on the geometry of feedback response fields and projections Summation of classical and inverse response accounts for surround facilitation.