Contrast and pattern adaptation in visual cortex share a common gain control mechanism.

Neuronal populations in primary visual cortex adapt both to stimulus contrast and to the probability of occurrence of visual patterns. Previous work showed that the magnitude of the population response follows a separable power-law function of contrast and stimulus probability, suggesting the existence of a shared gain mechanism. Here we ask whether a similar equivalence extends beyond response magnitude to the full distribution of activity across neurons within a trial. Across a wide range of adaptation states, we find that population responses are highly sparse and well described by a zero-inflated log-normal distribution. In this model, a fraction P0 of neurons remain silent, while the nonzero responses follow a log-normal distribution characterized by the mean (μ) and variance (σ2) of log activity. We find that both contrast and pattern adaptation produce coordinated changes in μ and P0 while leaving σ2 approximately invariant. As a result, responses across all adaptation conditions collapse onto a one-dimensional manifold in parameter space. A simple linear-nonlinear population model with fixed nonlinearity and input variance reproduces these observations when adaptation acts solely by modulating the mean input to the population. Together, these findings support the idea that contrast and pattern adaptation rely on a shared gain control mechanism that shifts the operating point of cortical populations while preserving the overall structure of their response distribution.NEW & NOTEWORTHY Contrast adaptation and pattern adaptation are often studied as distinct phenomena. We show that, at the level of population response distributions in V1, both forms of adaptation induce the same low-dimensional transformation: coordinated shifts in sparsity and mean activity with preserved log-variance. Across all conditions, responses collapse onto a one-dimensional manifold consistent with modulation of a shared gain variable. These findings provide population-level evidence that contrast and pattern adaptation rely on a common gain control mechanism.