Computational and physiological investigations of information processing in auditory cortex

Thesis

Auditory cortex has been shown to play a critical role in a plethora of processes, including the extraction of complex acoustic features, auditory scene analysis, decision making, and learning. However, there are still many aspects of auditory cortex’s structure and function that we do not understand. In this thesis, I explored three separate but related questions regarding cortical tuning properties, inhibition and their interplay in adaptation in the auditory cortex of the ferret. Firstly, I investigated the spatial distribution of preferred frequencies (“tonotopy”) amongst cortical neurons in the ferret using 2-photon calcium imaging and electrophysiology, and compared it to the mouse. I found that cortical neurons in mice and ferrets have equivalent local heterogeneity in their tuning, while retaining a globally tonotopic map. Much of the observed heterogeneity in the tonotopic maps could be explained by the existence of neurons with complex receptive fields. Secondly, I developed electrophysiological and imaging approaches in order to study the properties of excitatory and inhibitory neurons, allowing me to label and record from excitatory and subclasses of inhibitory neurons. I did not find significant differences in the proportions of tuned neurons across neuron classes, or in their tuning characteristics. I also found that the cotuning within and between classes are similar. Lastly, I explored the role of auditory cortex in adaptation to reverberation: What is the optimal transformation from reverberant to anechoic sounds in a statistical model, and can this model explain the robust representation of natural sounds in auditory cortex? The model recapitulated known properties of auditory cortical neurons, in addition to making novel predictions which I confirmed using electrophysiological recordings. These predictions were: (1) the inhibitory component of neuronal receptive fields shifts in time in proportion to the amount of reverberation, and (2) the degree of this inhibitory shift is frequency dependent. Taken together, these findings shed new light onto the organization and function of auditory cortex, providing exciting avenues for future research.

Authors: Ivanov, A

• DOI: 10.5287/ora-aekjneoqd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: auditory cortex