Neural representation of intraoral olfactory and gustatory signals by the mediodorsal thalamus in alert rats

Abstract

The mediodorsal thalamus is a higher-order thalamic nucleus involved in a variety of cognitive behaviors, including olfactory attention, odor discrimination, and the hedonic perception of flavors. Although it forms connections with principal regions of the olfactory and gustatory networks, its role in processing olfactory and gustatory signals originating from the mouth remains unclear. Here, we recorded single-unit activity in the mediodorsal thalamus of behaving rats during the intraoral delivery of individual odors, individual tastes, and odor-taste mixtures. Our results are the first to demonstrate that neurons in the mediodorsal thalamus dynamically encode chemosensory signals originating from the mouth. This chemoselective population is broadly tuned, responds with excitation and suppression, and represents odor-taste mixtures differently than their odor and taste components. Furthermore, a subset of chemoselective neurons encoded taste palatability. Our results further demonstrate the multidimensionality of the mediodorsal thalamus and provides additional evidence of its involvement in processing chemosensory information important for consummatory behaviors. SIGNIFICANCE STATEMENTThe perception of food relies upon the concurrent processing of olfactory and gustatory signals originating from the mouth. The mediodorsal thalamus is a higher-order thalamic nucleus involved in a variety of chemosensory-dependent behaviors and connects the olfactory and gustatory cortices with prefrontal cortex. However, it is unknown how neurons in the mediodorsal thalamus process intraoral chemosensory signals. Using tetrode recordings in alert rats, our results are the first to show that neurons in the mediodorsal thalamus dynamically represent olfactory and gustatory signals from the mouth. Our findings suggest that the mediodorsal thalamus is a key node between sensory and higher-order cortical areas for processing chemosensory information underlying consummatory behavior.