This work aims to develop a model for brainstem taste processing that takes account of the full array of sensory influences, and relates sensory responsiveness to functionally significant anatomy. Unlike most studies of central gustatory processing, our investigations make a targeted effort to analyze neurophysiological responses in the rostral nucleus of the solitary tract (rNST) and parabrachial nucleus (PBN) arising from each of several taste bud groups on the tongue and palate, and from oral somatosensory receptors. A comprehensive analysis is crucial. Both taste and somatosensory modalities are represented in these classical """"""""gustatory"""""""" relays. Investigating the representation of different taste bud groups is vital due to their heterogeneous chemosensitivities and distinctive effects on feeding. Our previous studies demonstrated that these varied influences are organized into orderly topographies in rNST and PBN, topographies characterized both by orotopy and partial segregation between modalities. More recent evidence is suggestive of further segregation by chemical sensitivity (chemotopy). Despite orderly mapping, convergence of afferent influences onto single cells is a salient feature of processing. Convergence is important because a myriad of taste, tactile, and thermal signals combine to elicit the complex experience of flavor and influence ingestion. The proposed experiments build on these observations. In rNST, we will specify the relationship between response topography and anatomy more precisely by relating sensory characteristics to subnuclear organization and connectivity, and further investigate the topographic organization of chemosensitivity. In PBN, we will elucidate the principles by which convergent neurons sum information, and also define sensory signals impinging on the 2nd-order relay from a recently described source, the paratrigeminal nucleus. Taste and oral somatosensory information interact with visceral signals, homeostatic state, and learning to regulate eating. In particular, orosensory signals influence the amount and type of food eaten.
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