PROJECT SUMMARY Cortical taste responses reflect sensory stimulation, perception, and behavioral decisions. These responses are the result of interactions among several brain areas. Ascending signals from the thalamus provide information from the periphery, but there are also recurrent interactions among several forebrain areas, including massive descending feedback connections to thalamus. Using this circuitry, animals must rapidly decide whether they will consume or expel a substance applied to the tongue. This behavior is natural, requires no training, and has obvious behavioral correlates that reflect the consumption or expulsion decision. Understanding how multiple brain areas interact to produce responses, perception, and behavior is a major goal of systems neuroscience, and the gustatory system is well suited to this pursuit. Recent work from a number of labs has gone far to characterize the nonlinear population dynamics of cortical taste activity, and has begun to unravel the inter-regional interactions that generate said dynamics, most notably with regard to the basolateral amygdala (Lin, et al., 2021; Mahmood, et al., 2023). Thalamo-cortical interactions have been slower to yield to scrutiny, however, because of the intense difficulty of even recording from taste thalamus in awake animals—something that has only been done a few times (e.g., Liu and Fontanini, 2015). We propose to explore the relationship between ensemble activity in the gustatory thalamus and ensemble activity in the gustatory cortex. There have been few studies of physiological responses in gustatory thalamus, and no studies where gustatory thalamus neurons have been recorded simultaneously with gustatory cortical neurons. New methods using high-density silicon electrodes now allow action potentials of afferent neurons and local neurons to be distinguished, allowing thalamic axons and cortical neurons to be recorded at a single site in the cortex. We will validate and employ these methods to simultaneously record thalamic and cortical neurons in the gustatory system of awake behaving rats during taste deliveries followed by consumption or expulsion. By examining these structures in a system with tight linkages between cortical activity and behavior, we expect to uncover new principles of interaction between thalamus and cortex.