Distal connectivity causes summation and division across mouse visual cortex.

Neurons in different locations across the cortex are connected through polysynaptic networks involving both excitation and inhibition. To probe the functional effect of such networks, we used optogenetic stimulation to trigger antidromic spikes in a local region of primary visual cortex (V1). This local activity had two effects at distal V1 locations: summation and division. The balance between the two depended on visual contrast, and a normalization model precisely captured these effects.