Information on Oral Temperature is More Robustly Encoded Than Taste in Neurons of the Mouse Gustatory Cortex

The gustatory cortex (GC) has traditionally been studied for its role in processing taste stimuli at a fixed temperature. The GC neurons respond to compounds representing different taste qualities and their hedonic value with time-varying and lick-related patterns of activity. However, a growing body of experimental work indicates that GC neurons can also respond to non-gustatory components of oral stimuli, including temperature, a prominent feature of the sensory properties of food and beverages. In this study, our objective is to evaluate the neural saliency of GC neurons in encoding chemosensory taste information at room temperature compared to their responsiveness to oral thermal information, specifically deionized water in the absence of classical taste qualities. To address this question, we recorded spiking activity from over 900 single GC neurons in mice allowed to freely lick to receive four liquid gustatory stimuli at room temperature or deionized water at different non-nociceptive temperatures. We then used a Bayesian analysis approach to determine classification scores for spike trains, considering both the rate and phase codes in response to the different stimuli. Our findings suggest that a classification approach that relies primarily on rate information, with a secondary contribution from phase, is optimal to distinguish between gustatory stimuli or water temperature. Surprisingly, we also observed that the number of GC neurons correctly classifying the stimulus is larger for thermal stimuli than for chemosensory stimuli, indicating that fluid temperature is more strongly encoded and thus more neurally salient than taste information.