Contextual modulation is a stable feature of the neural code in auditory cortex of awake mice

Abstract

The perceptual salience of a sound depends on the acoustic context in which it appears, and can vary on a timescale of milliseconds. At the level of single neurons in the auditory cortex, spectrotemporal tuning for particular sounds is shaped by a similarly fast and systematic nonlinear sensitivity to acoustic context. Does this neuronal context sensitivity "drift" over time in awake animals, or is it a stable feature of sound representation in the auditory cortex? We used chronically implanted tetrode arrays in awake mice to measure the electrophysiological responses of auditory cortical neurons to spectrotemporally complex, rapidly varying sounds across many days. For each neuron in each recording session, we applied the nonlinear-linear "context model" to estimate both a principal (spectrotemporal) receptive [fi]eld and a "contextual gain [fi]eld" describing the neurons nonlinear sensitivity to acoustic context. We then quanti[fi]ed the stability of these [fi]elds within and across days, using spike waveforms to match neurons recorded in multiple sessions. Contextual gain [fi]elds of auditory cortical neurons in awake mice were remarkably stable across many days of recording, and comparable in stability to principal receptive [fi]elds. Interestingly, there were small but signi[fi]cant effects of changes in locomotion or pupil size on the ability of the context model to [fi]t temporal fluctuations in the neuronal response. We conclude that both spectrotemporal tuning and nonlinear sensitivity to acoustic context are stable features of neuronal sound representation in the awake auditory cortex, which can be modulated by behavioral state.