Baseline activity of V1 interneurons connects pupil-linked arousal to engaged behavioral state

Humans and rodents alternate between discrete, persistent behavioral states during perceptual decision-making. For example, trials can be clustered into states of engaged, disengaged, and biased decision-making strategies. In mice, the probability of being in an engaged state exhibits an inverted-U relationship with baseline pupil-linked arousal, consistent with the Yerkes-Dodson Law. We replicated this relationship in mice (N=11; audio-visual change detection task) and showed that it generalizes to humans (N=69; auditory detection task). We then examined its neural basis, using simultaneous pupillometry and electrophysiological recordings in mouse V1. A nonlinear mediation model revealed that baseline activity of putative fast-spiking interneurons, but not putative pyramidal neurons, made a significant statistical contribution to the inverted-U shaped relationship between pupil-linked arousal and engaged-state probability. These findings are consistent with the idea that arousal may shape behavioral states by modulating baseline inhibitory activity within a primary sensory region.