The impact of parvalbumin interneurons on visual discrimination depends on strength and timing of activation and task difficulty

Abstract

Parvalbumin-expressing (PV) cells are the most common class of inhibitory interneurons in the visual cortex. They are densely connected to excitatory cells and play important roles in balancing cortical circuit activity and learning. PV cell activation is a tool to inactivate cortical regions to establish their role in visual processing. However, it is not established how moderate activation affects behaviour and how effects depend on activation strength, timing and task difficulty. We therefore investigated how these three major factors affect performance of mice in a go/no-go orientation discrimination task. We tested discrimination performance with different strength and timing of PV cell activation in V1 and with different task difficulty levels. We found that PV cell activation improved performance in easy discriminations when stimulating with moderate laser powers only during the initial 120 ms from stimulus onset, corresponding to the initial feedforward processing sweep across the cortical hierarchy. In the same animals, PV cell activation did not aid performance in difficult discriminations. However, in both easy and difficult discriminations, optimal behavioural performance required undisturbed late phase activity beyond 120 ms, highlighting the importance of sustained activity in V1. Combining the optogenetic activation of PV cells with two-photon imaging showed that behavioural changes were associated with changes in stimulus response selectivity in V1. Thus, our results demonstrate that early and sustained activity in V1 is crucial for perceptual discrimination and delineate specific conditions when PV cell activation shapes neuronal selectivity to improve behaviour. O_LIEffects of moderate optogenetic PV cell activation on behaviour are time window specific C_LIO_LIBenefits of increased PV cell-mediated inhibition depend on task difficulty C_LIO_LIOptimal behavioural performance requires sustained V1 activity in both easy and difficult discriminations C_LIO_LIBehavioural changes with PV cell activation are reflected by changes in the selectivity of V1 neurons C_LI