Inhibitory Gating of Coincidence-Dependent Sensory Binding in Secondary Auditory Cortex

Abstract

Integration of multi-frequency sounds into a unified perceptual object is critical for recognizing syllables in speech. This "feature binding" relies on the precise synchrony of each components onset timing, but little is known regarding its neural correlates. We find that multi-frequency sounds prevalent in vocalizations, specifically harmonics, preferentially activate the mouse secondary auditory cortex (A2), whose response deteriorates with shifts in component onset timings. The temporal window for harmonics integration in A2 was broadened by inactivation of somatostatin-expressing interneurons (SOM cells), but not parvalbumin-expressing interneurons (PV cells). Importantly, A2 has functionally connected subnetworks of neurons encoding harmonic, but not inharmonic sounds. These subnetworks are stable across days and exist prior to experimental harmonics exposure, suggesting their formation during development. Furthermore, A2 inactivation impairs performance in a discrimination task for coincident harmonics. Together, we propose A2 as a locus for harmonic integration, which may form the circuit basis for vocal processing.