Persistent activity in primate auditory cortex evoked by sensory stimulation

Persistent activity, the elevated firing of a neuron after the termination of a stimulus, is hypothesized to play a critical role in working memory. This form of activity is therefore typically studied within the context of a behavioural task that includes a working memory component. Here we investigated whether persistent activity is observed in sensory cortex and thalamus in the absence of any explicit behavioural task. We recorded spiking activity from single units in the auditory cortex (fields A1, R and RT) and thalamus of awake, passively-listening marmosets. We observed persistent activity that lasted for hundreds of milliseconds following the termination of the acoustic stimulus, in the absence of a task. Persistent activity was observed following both adapting and sustained responses during the stimulus and showed similar stimulus tuning to these evoked responses. Persistent activity was also observed following suppression in firing during the stimulus. These response types were observed across all cortical fields tested, but were largely absent from thalamus. As well as being of shorter duration, thalamic persistent activity emerged following a longer latency than in cortex, indicating that persistent activity may be generated within auditory cortex during passive listening. Given that these responses were observed in the absence of a explicit behavioural task, persistent activity in sensory cortex may have functional importance beyond storing task-relevant information in working memory.