PROJECT SUMMARY Eating and drinking are rapid processes, but their postingestive effects are slow and delayed. How do animals correctly associate these delayed effects (detection of nutrients or toxins in the gut) with transient stimuli like tastes and smells that precede them by minutes or hours? To gain insight into this question, I leveraged the fact that mice learn to associate novel, but not familiar, foods with gastric malaise signals to investigate what distinguishes the neural representations of flavors that promote learning versus those that do not. I surveyed brainwide expression of the immediate early gene Fos during drinking and during postingestive malaise and discovered that distinct functional networks of flavor-selective brain regions are recruited at different phases of postingestive learning. This led to two key hypotheses about how the brain is able to link tastes and flavors to delayed postingestive feedback. During the postdoctoral phase (K99/Aim 1) of this proposal, I will test the hypothesis that an amygdala network centered on the central amygdala (CEA) represents novel flavors during drinking and that this representation is then reactivated when postingestive feedback signals from the gut arrive, providing temporal overlap between the flavor representation and feedback that promotes learning. I will first use high-density Neuropixels recordings to demonstrate that CEA novel flavor representations are reactivated during postingestive malaise (Aim 1.1) and then use optogenetic activation of CEA novel flavor ensembles to show that these postingestive reactivations are sufficient to drive learning (Aim 1.2). In the independent phase (R00/Aim 2), I will test the hypothesis that a limbic network centered on the lateral septum (LS) blocks these novel flavor reactivations to gate the formation of postingestive associations when flavors are recognized as familiar and safe. I will first use axon terminal photostimulation to identify the specific LS projection that gates learning (Aim 2.1) and then combine this manipulation with high-density neural recordings in downstream regions (Aim 2.2) and brainwide Fos imaging (Aim 2.3) to investigate how LS activity blocks the formation and reactivation of novel flavor representations. These experiments will generate key insights into the cross-region neural mechanisms that support conditioned taste aversion and postingestive learning. During the K99 phase, I will gain crucial technical expertise — in Neuropixels electrophysiology, advanced computational tools, and activity-dependent genetic labeling — and professional development that will be essential for my independent lab’s mission. Our ultimate goal will be to uncover general principles by which interoceptive signals engage the brain to control behavior and how the mechanisms underlying postingestive learning go awry in eating disorders and obesity.