We like to think of taste as working relatively simply: a sweet taste is recognized as sweet by virtue of activating certain parts of the tongue, and that information is used to drive neurons that cause us to eat more of whatever food is in our mouths. The truth, however, is much more interesting. A taste hits the tongue, and complex circuits in the brain go into action, passing food-related information back and forth as the system as a whole decides what to do, in light of experience and current conditions (e. g., hunger). My lab studies this process by recording from multiple parts of the taste system while active rats are sampling various tastes. Our work allows us to observe this decision-making process in action, as taste cortex realizes, sequentially, that a taste is on the tongue, that the taste is (say) sugar, and that it (the rat) currently likes the taste. The research that we're currently proposing will build on this foundation. First, we will do a direct, rigorous test of this characterization of taste processing in cortex, by measuring how cortical neurons handle salt. As the concentration of a salt solution increases, it becomes first more pleasing (just as a little salt on food is good) and then more aversive (like sea water);our Preliminary data shows us that, as expected, cortical neurons first code the concentration (what the taste is) and then its palatability (whether the taste is likeable). Our next experiment will look at where that information in cortex comes from, by recording from cortex and the amygdala (the seat of emotion in the brain) simultaneously. Does cortex figure this stuff out by itself, or does amygdala do the work, or do cortex and amygdala work hand-in-hand? This dual recording experiment will give us important clues. Finally, to test whether the clues that we observe mean what we think that they do, we will do one more experiment, in which we electrically stimulate the amygdala while the rat is in the midst of tasting;to the extent that the amygdala is important for the processing done by cortex, amygdalar stimulation should derail this cortical processing. As a whole, this research project has the potential to completely change the way we think about taste, and to usher in new thinking about perception in general-thinking that makes a great deal more biological sense, given the complexity of brain circuitry.
We decide whether a food is worth eating on the basis of a host of factors, including experience and our current physiological state, and as such these decisions involve a relatively large part of our brains. Using salt as a probe, we will gather novel data providing important clues to precisely how the many neurons, and multiple brain regions, that make up our taste system work together to perform this feat. The more systemic understanding of taste that will emerge from this research will help us to develop tools to fight a spectrum of eating disorders, to aid parents with child feeding issues, and to cure vexing taste abnormalities such as develop during pregnancy.
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