Abstract
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). Although neurons in the two regions display different response properties, like response latency, firing threshold or tuning bandwidth, it is still not clear whether they process sound in a distinct way. 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. AAF neurons also display faster and more transient responses than A1 neurons. Additionally, offset responses in AAF – unlike in A1, increase with sound duration. Local field potential (LFP) and laminar analyses suggest that the differences in sound responses between these two primary cortices are both of subcortical and intracortical origin. These results emphasize the potentially critical role of AAF for temporal processing. Our study reveals a distinct role of two primary auditory cortices in tone processing and highlights the complexity of sound encoding at the cortical level.
Highlights
For sound perception, auditory signals have to travel a long way from the cochlea, through the cochlear nuclei, superior olivary complex, inferior colliculus, and auditory thalamus up to the auditory cortex where two regions, A1 and anterior auditory field (AAF), receive them in parallel
We first confirmed the primary nature of A1 and AAF by verifying that these two cortical regions receive parallel signals from medial geniculate body (MGB), combining in vivo multi-electrode electrophysiological recordings and retrograde tracing
Confocal imaging of the thalamocortical slices revealed a robust signal in the MGB, confirming that both A1 (Fig. 1a) and AAF (Fig. 1b) receive signals from the auditory thalamus[2,3]
Summary
Auditory signals have to travel a long way from the cochlea, through the cochlear nuclei, superior olivary complex, inferior colliculus, and auditory thalamus up to the auditory cortex where two regions, A1 and AAF, receive them in parallel. AAF neurons show faster temporal modulation than A1 neurons[9], significantly shorter receptive field durations and latencies[10], better timing precision[11], and fast-pass selectivity for the rate of frequency-modulated sweeps[12]. Despite this knowledge, it is still not clear whether their role in sound processing is distinct. Offset responses were reported previously in auditory cortex (ACx) neurons[13,14] and their strength was compared between different auditory fields[15,16,17] but their distinct properties in A1 and AAF were not described. Our study reveals a crucial role of AAF in processing tone offsets, and thereby the possibility of distinct functions in sound processing for these two primary auditory cortices
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