Cellular and synaptic mechanisms of cortical taste coding in awake-behaving mice

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DESCRIPTION (provided by applicant): The exact nature and mechanism of encoding chemical stimuli in primary gustatory cortex is a matter of debate. Chronic extracellular recordings from awake-behaving rats suggest a dynamic and distributed code 4-10. This model emphasizes the unique spatio/temporal patterns of activity among groups of broadly tuned neurons acting as dynamic ensembles. However, recent data from anesthetized mice using in-vivo calcium imaging show a precise gustatopic map of primary tastes in the cortex 1. This suggests a coding scheme of sharply tuned gustatory cortical neurons arranged in topographically organized clusters. While the evidence for an organized cortical map representing primary tastes is intriguing, enthusiasm for such a map is tempered by the reliance on anesthetized animals 1-3. Anesthesia is well known to cause aberrant and artificial cortical network dynamics, significantly affecting processing of sensory stimuli 11. This proposal will resolve this problem by directly testing the general hypothesis that taste responsive neurons in gustatory cortex from awake-behaving mice are narrowly tuned and topographically organized. This will be accomplished by using a unique combination of in vivo extracellular and whole-cell patch-clamp electrophysiology, with a novel head-restrained mouse preparation that allows precise and systematic targeting of recordings throughout gustatory cortex in awake-behaving mice. The specific aims will study the functional organization of the gustatory cortex in awake-behaving animals with unprecedented detail, from the network-level to detailed synaptic mechanisms. Aim 1: Taste responses in gustatory cortex are narrowly tuned and functionally organized into topographic clusters in awake-behaving mice. Aim 2: Single-unit taste responses reflect mapped multi-unit activity. Aim 3: A balance of excitatory and inhibitory synaptic conductances drive taste responses in gustatory cortical neurons and shapes tuning.