Temporal and rate representations of time-varying signals in the auditory cortex of awake primates

Because auditory cortical neurons have limited stimulus-synchronized responses, cortical representations of more rapidly occurring but still perceivable stimuli remain unclear. Here we show that there are two largely distinct populations of neurons in the auditory cortex of awake primates: one with stimulus-synchronized discharges that, with a temporal code, explicitly represented slowly occurring sound sequences and the other with non-stimulus-synchronized discharges that, with a rate code, implicitly represented rapidly occurring events. Furthermore, neurons of both populations displayed selectivity in their discharge rates to temporal features within a short time-window. Our results suggest that the combination of temporal and rate codes in the auditory cortex provides a possible neural basis for the wide perceptual range of temporal information.