Fluctuating internal states mediate neural-behavioral covariations in V1

Our perception of the world depends on a complex interplay between external sensory inputs and our internal states. How and where in the brain these interactions are implemented remain poorly understood. To address these questions, we measured membrane potential (V_m) of single V1 neurons in macaque monkeys performing a reaction-time visual detection task. Here we show that most V1 neurons gradually depolarize in preparation for target onset, and that variations in this buildup are correlated with the monkey's reaction times. Further, we show that fluctuations in V_m after target onset are correlated with choice, and that these covariations strongly depend on the location and contrast of the target. Finally, we show that a simple computational model with fluctuating multiplicative gain can account for our results. Thus, the surprising covariations between V_m of single V1 neurons and behavior are implemented by internal-state-related nonlinear modulations operating at, or before, V1.