Neural Processing of Taste-Related Signals in the Mediodorsal Thalamus of Mice

Abstract

Our consummatory decisions depend on the taste of food and the reward experienced while eating, which are processed through neural computations in interconnected brain areas. Although many gustatory regions of rodents have been explored, the mediodorsal nucleus of the thalamus (MD) remains understudied. The MD, a multimodal brain area connected with gustatory centers, is often studied for its role in processing associative and cognitive information and has been shown to represent intraorally delivered chemosensory stimuli after strong retronasal odor-taste associations. Key questions remain about whether MD neurons can process taste quality independently of odor-taste associations and how they represent extraoral signals predicting rewarding and aversive gustatory outcomes. Here, using C57 male and female mice we present electrophysiological evidence demonstrating how MD neurons represent and encode 1) the identity and concentrations of basic taste qualities during active licking, and 2) auditory signals anticipating rewarding and aversive taste outcomes. Our data reveal that MD neurons can reliably and dynamically encode taste identity in a broadly tuned manner and taste concentrations with spiking activity positively and negatively correlated with stimulus intensity. Our data also show that MD can represent information related to predictive cues and their associated outcomes, regardless of whether the cue predicts a rewarding or aversive outcome. In summary, our findings suggest that the mediodorsal thalamus is integral to the taste pathway, as it can encode sensory-discriminative dimensions of tastants and participate in processing associative information essential for ingestive behaviors.

Significance Statement Dietary decisions are driven by the taste of the food and the reward experienced while eating. This information is processed through neural computations across interconnected brain areas. Given its neural connections, the mediodorsal thalamus (MD) could be part of this network. However, its involvement in gustatory processing is largely ignored. This study examines how MD neurons respond to taste quality, intensity, and expectation by analyzing the electrical activity of MD neurons in mice allowed to freely lick a spout to obtain different tastes. Our findings support the idea that the MD is part of the brain network responsible for processing sensory and associative information relevant to eating.