Context-dependent activation of V1 parvalbumin interneurons enhances visual discrimination.

Inhibition is critical for balanced cortical activity and learning. Parvalbumin-expressing cells (PV) are the most common cortical inhibitory interneurons. Strong PV activation inactivates cortical regions. However, the effect of moderate activation on vision and dependence on activation strength, timing, and task difficulty is not established. We investigated these three major factors during visual discriminations in mice. Moderate PV activation in the primary visual cortex (V1) improved easy but not difficult discriminations. It did so only during the initial 120 ms after stimulus onset, corresponding to the initial feedforward processing sweep. Both easy and difficult discriminations required undisturbed late phase activity beyond 120 ms, highlighting the importance of sustained V1 activity. Combined optogenetic activation and two-photon imaging showed that behavioral effects were associated with V1 response selectivity changes. A circuit model with nonlinear activation and strong competitive interactions between V1 cells captured the data. This demonstrates that early and sustained V1 activity is crucial for perceptual discrimination and delineates conditions when PV activation shapes neuronal selectivity to improve behavior.