Sound processing in the mouse auditory and dorsal neocortices

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Afrashteh, Navvab
University of Lethbridge. Faculty of Arts and Science
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Lethbridge, Alta. : University of Lethbridge, Dept. of Neuroscience
There are two theories of how the neocortex processes sound. The feature detection theory posits that cortical neurons process sound to extract its features, whereas, in the decoding theory, cortical neurons are viewed as the decoders of “sound objects”: specific spectrotemporal patterns. In this thesis, I assess both theories in a set of longitudinal experiments with simple and complex sounds presented to awake and isoflurane-anesthetized mice. For the feature detection theory, the auditory cortex (AC) maps of tone frequency and frequency modulation (FM) rate are updated. In these maps, new areas and topographic gradients are discovered. The maps are stable across a recording period and reproducible between brain states. Moreover, a region in the primary AC encodes for the FM direction, crucial in the perception of complex sounds. Finally, fast FM rate topographic areas are the most involved in processing MVocs. For the prediction theory, both AC and the dorsal neocortex (DC) were considered. First, network analysis revealed that AC and DC work together to process sounds, with the interaction level determined by acoustic complexity and brain state. Second, a classification analysis showed that both cortices are informative of the stimuli, with AC twice as informative as DC. Isoflurane-anesthesia maintains the informative power of AC but vanishes the power of DC, except for simple sounds. Lastly, a regression analysis between sounds and behavior (predictors) and the cortical activity (response) was performed to assess the power of stimuli to explain the cortical activity. The sound stimuli could explain AC and DC activity up to 68% and 32%, respectively. The higher explanation power of sound is observed for more complex sounds in the awake state. To conclude, despite the simplicity of the feature detection theory, the detection theory provides a superior understanding of the neocortical functions in auditory processing.
anesthesia , auditory object , auditory system , awake , brain state , calcium imaging , cortex , cortical activity estimation , cortical streams theory , evoked cortical activity , feature map , frequency modulations , functional characterization , functional connectivity , functional map , GCaMP , mesoscale , mouse , neuroscience , object theory , optical imaging , response modeling , sensory processing , sound classification , sound decoding theory , sound processing , Spatiotemporal structure , stimulus complexity , tonotopy , vocalization , widefield , rodents , hearing , computational neuroscience , systems neuroscience , spectrotemporal , acoustic feature , sensory perception , Mice--Nervous system--Research , Neocortex--Research , Auditory cortex--Research , Auditory pathways--Research , Auditory perception--Research , Brain--Research , Neurosciences , Mice as laboratory animals , Dissertations, Academic