Behaviorally relevant decision coding in primary somatosensory cortex neurons

Primary sensory cortex is thought to process incoming sensory information, while decision variables important for driving behavior are assumed to arise downstream in the processing hierarchy. We used population two-photon calcium imaging and targeted two-photon optogenetic stimulation of neurons in layer 2/3 of mouse primary somatosensory cortex (S1) during a texture discrimination task to test for the presence of decision signals and probe their behavioral relevance. Small but distinct populations of neurons carried information about the stimulus irrespective of the behavioral outcome (‘stimulus neurons’), or about the choice irrespective of the presented stimulus (‘decision neurons’). Decision neurons show categorical coding that develops during learning, and lack a conclusive decision signal in miss trials. All-optical photostimulation of decision neurons improves behavioral performance, establishing a causal role in driving behavior. The fact that stimulus and decision neurons are intermingled challenges the idea of S1 as a purely sensory area, and causal perturbation suggests a direct involvement of S1 decision neurons in the decision-making process.