Dynamics and maintenance of categorical responses in primary auditory cortex during task engagement

Grouping sets of sounds into relevant categories is an important cognitive ability that facilitates the association of stimuli with appropriate goal-directed behavioral responses. In perceptual tasks, a prominent role of primary auditory cortex (A1) is to multiplex the encoding of sound sensory features and task variables. Here we investigated the involvement of A1 in initiating sound categorization. We trained ferrets to discriminate click trains of different rates in a Go/No-Go delayed categorization task and recorded neural activity during both active behavior and passive exposure to the same sounds. Purely categorical response components were extracted and analyzed separately from sensory responses to reveal their contributions to the overall population response throughout the trials. We found that population-level representation of Go/No-Go behavioral categories emerged during sound presentation and was present in both active behavioral and passive states. However, upon task engagement, categorical responses to the No-Go category became suppressed, leading to an asymmetrical representation of the Go stimuli relative to the No-Go sounds and prestimulus baseline. At stimulus offset, the population code changed abruptly but categorical representation was maintained during the delay period. Categorical responses extracted from the stimulus period correlated with the ones found in the delay epoch, suggesting an early contribution of A1 to stimulus categorization.