Project Summary / Abstract Abnormal interoceptive processing is observed across psychiatric and neurological conditions wherein core symptoms are motivated by diffuse bodily feeling: pervasive negative mood in Major Depression, compulsive urge in Obsessive Compulsive Disorder, urge to tic in Tourette Syndrome, and craving in addiction. Despite the prevalence of interoceptive abnormality, there is a scarcity of data on neurovisceral interactions in clinical populations. This knowledge gap can be attributed in part to a need for objective, neural measures of interoceptive processing. A candidate neural measure is the heartbeat evoked potential (HEP), a brain electrophysiological signal that is time-locked to the heartbeat and thought to index baroreceptor sensation in the chest cavity. While promising, basic characteristics of this signal are unknown, which limits its application to mechanistic and clinical research. Cortical sources of the HEP have been identified in the insula, yet spatial and temporal characteristics diverge across experimental paradigms. This suggests multiple functional correlates and cortical sources of the HEP index, including the insula. An added challenge is that the insula may be too deep for non-invasive recording and modulation, which necessitates invasive neural recording to explain non-invasive measures. Aim 1 validates neural source generators of the HEP with simultaneous invasive stereoelectroencephalography and dense array EEG on the scalp surface, while patients complete a battery of interoceptive tasks. Aim 2 investigates neural network dynamics during interoceptive attention, arousal and anticipation: theorizing that key clinical symptoms (e.g., tic, compulsions, negative mood) are learned behaviors in response to interoceptive cues, we test the specific hypothesis that interoceptive activity is a predictor of reward-based decisions, particularly when decision-making demands a go with your gut strategy as reward outcomes are learned. Critically, Aim 3 then applies a deep breathing strategy to strategically perturb cardiac dynamics and disambiguate functional correlates of the HEP signal. Outcomes define properties of the HEP signal that must be known for this measurement strategy to inform and validate models of abnormal interoceptive circuit dynamics involving maladaptive responses to bodily distress.