THALAMO-INSULAR BASIS FOR UPDATING PHYSIOLOGICAL NEEDS

Physiological needs, such as thirst and hunger, produce powerful motivation for behaviors that are essential for survival. Yet, how the brain estimates these needs remains unknown. It is unclear whether the brain continuously monitors bodily signals to create real-time representations, or if existing internal representations are only updated when meaningful changes occur. Understanding such processes is essential for revealing how physiological needs shape behavior. To address this question, we developed a novel behavioral apparatus and combined it with longitudinal microprism-based two-photon imaging of the insular cortex to track its activity dynamics across conflicting physiological needs and need-fulfilling rewards. We then used optogenetic inhibition to manipulate thalamic internal sensory inputs to the interoceptive insular cortex. We found that this prevents the updating of insular cortex representations of thirst and hunger, thereby keeping its activity in its initial physiological need state. Consequently, cue-driven feeding and drinking become stuck in the initial thirsty or hungry state, preventing behavioral expression of satiety. In further support of the updating model, insular cortex activity represents need-specific predictions as well as sensory information when learned expectations are met. Moreover, violating these learned expectations evokes widespread need-specific prediction error signals. Our results thus reveal a thalamo-cortical basis for updating physiological needs in the brain.