Obesity is a national epidemic. Among other maladies, obesity underlays most type 2 diabetes and a significant proportion of hypertension. Obesity occurs because individuals ingest more calories than they expend. This takes place when the reward value of the food is greater than the sum of the satiety signals arising in the gut. The goal of this research is to understand the neural mechanisms that govern the decision to ingest or reject the contents of the oral cavity, the fundamental act of feeding behavior. The neural substrates for this decision are complete in the brainstem. The oral tactile, thermal, and gustatory afferent activity that guides ingestive behavior first reaches the brain in the pons and medulla. The motor neurons that produce ingestive behavior also are located in the brainstem. The response elicited by these oral stimuli can be switched from ingestion to rejection by vagal visceral activity that first reaches the CNS in the medulla. Nevertheless, control of ingestion requires connections to and from the forebrain because disconnecting it from the brainstem eliminates voluntary eating. Using behavioral, neuroanatomical, neurochemical, and electrophysiological analysis, this project will test hypotheses about how the reward value of gustatory and other oral stimuli are elaborated in the brain. Specific experiments examine (1) how the gustatory sensory activity influences brain areas thought to be involved in producing reward, (2) the neural pathways for these rewarding sensory effects and (3) how other rewarding oral stimuli, such as temperature and texture, differ from taste in the hedonic domain. The answers to these questions will help us understand how a normally well regulated behavior, such as eating, can go so far awry as to cause an epidemic.
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