The broad, long term objectives of this project are to discover how neurons in the brain encode information about taste stimuli. Since the taste of food is a major determinant of food intake, this knowledge is an important foundation for understanding abnormalities of food intake, e.g. anorexia, obesity, etc. In addition, the study of how neurons convey information is crucial to the rational design of sensory prosthetics. To further our understanding of taste processing, the present project is focused on temporal coding in the nucleus of the solitary tract (NTS) and the parabrachial nucleus of the pons (PbN), respectively the first and second central relays in the rat taste system. HYPOTHESES are 1) Temporal characteristics of cooperative firing patterns among taste-responsive and mechanosensitive neurons in the NTS provide the basis for rapid assessment of taste stimuli 2) PbN activity will mirror activity of NTS cells in the initial response interval for all tastants, but become progressively more decorrelated as the response unfolds over time. Further, we propose that distinctions between hedonically positive and negative tastants will become more definitive in the later portions of the response. 3) The temporal patterns of taste responses in the PbN are both necessary and sufficient to convey a taste sensation of an identifiable quality. 4) Electrical stimulation of the waist area will evoke a taste-like sensation, but stimulation of the external lateral nucleus will evoke avoidance without a specifiable taste quality.
SPECIFIC AIMS : 1) Information contributed by temporal coding will be quantified by analyses of electrophysiological responses to taste stimuli recorded from ensembles of NTS cells in awake, behaving rats Taste stimuli and their binary mixtures, as well as tastants at varying concentrations will be presented. 2) Taste responses will be recorded simultaneously from ensembles of neurons in the NTS and PbN of awake behaving rats and the transfer of information between these two structures will be characterized. 3) Generalization of a conditioned aversion to lick-contingent electrical stimulation of the PbN will be used to a) demonstrate that the temporal pattern of electrical stimulation can mimic the perceptual properties and behavioral reactivity of either quinine or sucrose and b) construct a temporal sequence of electrical pulses which incorporates the critical features of the temporal pattern of electrical stimulation that, when used to drive activity in the PbN, will evoke specific taste sensations and appropriate behavioral reactions. We will electrically stimulate the waist area and external lateral subnuclei of the PbN in awake rats with pulse trains that mimic the PbN response to quinine (quinine simulation) or sucrose (sucrose simulation).
Since the sense of taste is at the core of our decisions of what to eat and what not to eat, the study of how the brain processes taste will advance our understanding of how these decisions are made and how they can go awry, as in obesity, for example, and adversely affect our health. In addition, the results of our proposed studies will provide basic principles about how neurons in the brain convey information about the world around us. These principles can then be applied to the design and implementation of brain-machine interfaces, such as sensory prostheses that are used to improve the lives of people with severe injuries to their limbs or spinal cord.
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