Newly Discovered Taste Map in the Brain

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By Keely Sudhoff, PhD

Sweet, salty, bitter, sour, and umami:  these are the five basic tastes our visitors learn about as part of the museum's Genetics of Taste research project.  It is the finely tuned array of these taste qualities which allows us to savor tasty meals or to take a sip of spoiled milk and toss it quickly down the drain.  We do not think about our actions; they are innate and we are primed to know the difference.  We taste for survival - bitter can alert us to poisons; sweet signals a large intake of energy (mmm, chocolate cake); umami informs us of savory proteins; salty helps us maintain cellular balance.

Scientists know we taste for survival but have wondered how taste messages are sent from the tongue to the brain.  Charles Zuker, a neuroscientist at Columbia University, is making breakthroughs in understanding this pathway.  He was responsible for discovering the "one taste, one cell" system in mammals (Chandrashekar et al. Nature 444, 288 (2006), Yamolinsky et al. Cell 139, 234 (2009)).  In short, he concluded that the taste cells in our tongue are highly specific, each cell expresses receptors that can only bind one basic taste.  After the target taste molecule binds it's receptor in the taste cell, a neural pathway then sends the signal to the brain.  But where in the brain? 

Previous brain models for taste identification suggested a broad pattern of neural recognition across taste qualities, but Zuker's most recent publication in Science this month (p. 1262) has shaken up the field of gustatory science. When artificial saliva containing different compounds was applied onto the tongues of anesthetized mice, Zuker's team was able to see discrete clusters of nerve cells fluoresce based on the selective response to the individual basic tastes of bitter, salt, sugar and umami. Moreover, these clusters of taste-specific neurons were located in precise and spatially segregated areas of the cortex (Figure 1).  Interestingly, the researchers did not find sour-selective neurons.  Zuker reasoned that this may be because those neurons exist outside the region of the cortex they surveyed.

So while we know for sure there is no taste map on the tongue, evidence suggests that there may be one in the brain.

blog post 09_2011

Figure 1: Labeled hot spots in the mouse gustatory cortex red (bitter), umami (yellow), sweet (green), and salty (orange).

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