Role of neural activity during inter-token intervals in sound sequence discrimination-1, Primary Auditory Cortex

Auditory neurons, in the midbrain and beyond, detect changes in repeating acoustic patterns. Most studies focus on mechanisms underlying such sensitivity and adaptation to regularity. However, regular sound patterns are crucial in social communication, stream-segregation and grouping in different species including humans. Thus, we address cortical selectivity to periodic or aperiodic sound sequences with multiple stimulus attributes. With single unit electrophysiology and two-photon calcium imaging in anesthetized and awake mouse auditory cortex, we observe subpopulations of neurons selective to periodicity or aperiodicity that lack generalization across period-length, frequency-content or inter-token-interval durations. Comparing results with or without inter-token-interval spiking activity, shows its profound role underlying selectivity to periodic or aperiodic sequences. The whole population average rate for periodic and aperiodic stimuli is identical but not following each period and stimulus-off-period. Hence, inter-token-interval activity, post each period builds up during the sequence providing information on selectivity.