Defining How the Tongue Knows Sweet from Sour
He has helped identify the cells, receptors and signaling mechanisms that govern what we taste. He has mapped how the five basic tastes— sweet, sour, salty, bitter and umami (savory)—are represented by distinct areas of the brain, and showed that each taste is hard-wired for a specific response, sending the appropriate signal to the brain. For example, triggering appetitive—or satisfying—responses when we taste something sweet, but evoking aversive behaviors when we taste something bitter.
“We are all born with a hard-wired attraction to sugar and an aversion to bitters,” said Zuker. “An organism’s survival can depend on its ability to distinguish attractive tastes like sweet from aversive ones like sour and bitter.”
Now, research from his lab at Columbia University Medical Center reveals the existence of special molecules that help the tongue communicate with the brain to correctly identify each taste. The findings were published Aug. 17 in Nature.
“This is a significant issue because the taste cells on your tongue only live for 10-15 days, so as new ones are born they need to reconnect with the correct neurons,” said Hojoon Lee, a postdoctoral associate in Zuker’s lab and lead author of the study.
Based on those findings, Lee and co-workers were then able to genetically engineer mice with rewired taste systems, fooling them into thinking sweet stimuli were bitter tastes and vice versa. “Step-by-step studies like this one are helping us decipher the wiring rules of one of the most basic of our senses,” said Lee.
In a parallel set of studies exploring how tastes are represented in the brain cortex, Yuequing Peng, another postdoctoral associate in Zuker’s lab, showed that by manipulating the brain areas encoding sweet and bitter taste they could directly control an animal’s internal representation, sensory perception and behavioral actions. “These results illustrate the ability of the taste cortex to recapitulate complex behaviors in the total absence of sensory input. In essence, we can make animals “sense” sweet or bitter, in the absence of an actual taste, by simply going into their brain and activating the right region,” said Peng.
Zuker, who joined Columbia in 2009 from the University of California, San Diego, is a professor of biochemistry and molecular biophysics and of neuroscience. He is also a principal investigator at Columbia’s Zuckerman Mind Brain Behavior Institute and an Investigator of the Howard Hughes Medical Institute.
“The taste system gives us a unique window into the workings of the brain; how detection by the tongue is transformed into perception, action and behaviors. Or how our internal state—whether we are sated or hungry—impacts our perceptions. Or how taste memories are encoded and decoded, so that a unique flavor can evoke such strong memories and emotions,” said Zuker.
“Columbia is an extraordinary place to carry out these studies, the breadth and depth of the neuroscience community here, and the new Zuckerman Mind Brain and Behavior Institute, create nothing short of a magical environment,” he added.