Akritas, Marios; (2022) Investigating the influence of acoustic and behavioural context on neural representations of sound in the awake mouse auditory cortex. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The context in which a sound is presented--- whether acoustic (e.g.: stimulus history and statistics) or behavioural (e.g.: subject’s arousal level)--- can modulate the sound's processing in the auditory system. However, in studies of the auditory cortex (ACtx), the models most often used are the linear Spectro-Temporal Receptive Field or other Linear-Non-linear models which do not allow for interactions between spectral or temporal elements in the receptive field. Moreover, relatively little is known about the potential effects of altering the long-term temporal dynamics of a stimulus (e.g.: temporal regularity or duration of stimulus on ~1 s timescales). We recorded extracellular electrophysiological activity in the ACtx of awake mice, along with their running, pupil diameter and facial movements, while they passively listened to acoustic stimuli. We recorded from the same site multiple times and matched units using waveform shapes. After fitting the responses of neurons to the Dynamic Random Chord stimulus using the Context Model (Williamson et al., 2016) we report that contextual sensitivity is an integral and stable feature of the neural code of the awake mouse (ACtx), that the average neuronal contextual modulation is qualitatively similar to that previously observed in the anaesthetized mouse but with faster temporal dynamics and that arousal and locomotion did not significantly affect the quality of these fits. We also report robust movements of the whisker pad, pinna and nose in response to noiseburst onsets, but only pinna movements at sound offsets. Furthermore, we report a subset of units which show a significant correlation between the amplitude of neural responses and that of facial movements. Our findings highlight the importance of: (i) acoustic context in shaping the neuronal responses of units in the awake mouse ACtx, and (ii) monitoring the movements of the animal as a means of control for auditory systems neuroscience experiments in awake mice.

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