Identifying functional roles of neural circuits in two primary auditory cortices

During sound perception, auditory signals have to travel a long way from the cochlea, through the subcortical areas, up to the auditory cortex. How each nucleus on this pathway - especially in the central auditory system - contributes to making sense of the acoustic world is far from understood. In the rodent auditory system, the primary cortex is subdivided into two regions, both receiving direct inputs from the auditory thalamus: the primary auditory cortex (A1) and the anterior auditory field (AAF). To deepen our general knowledge of auditory cortical processing, we studied what sound features are preferentially represented by primary auditory cortices, the spatial organization of these preferences, and their possible perceptual role. Using in vivo electrophysiological recordings in the mouse auditory cortex, we found that AAF neurons have significantly stronger responses to tone offset than A1 neurons. These results emphasize the potentially critical role of AAF for temporal processing. By combining electrophysiological recordings in AAF and auditory thalamus with antidromic stimulation, we revealed that cortical offset responses are inherited from the periphery, amplified, and generated de novo. Preventing offset responses in animals performing sound termination detection task decreased their ability to detect that the sound stopped, confirming the relevance of cortical auditory offset responses at the behavioral level. Additionally, by studying responses in A1 and AAF evoked by sounds with different spectral complexity, we found that responses in A1, but not in AAF, are influenced by the spectral complexity of the sound, suggesting that A1 is predominantly enrolled in the spectral processing. Our findings open new vistas into understanding the functional roles of A1 and AAF and more general auditory cortex in sound processing and perception. Identifying the specific functions of auditory cortical circuits paves the way for future understanding of the mechanisms behind impairments in spectral or temporal processing arising from both aging and disease.