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Your Brain Can Manipulate Tastes Such As Bitter And Sweet

Update Date: Nov 24, 2015 09:15 AM EST
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We have always given the credit of tasting to our tongues. However, scientists show that they can change the way mice can perceive taste just by manipulating brain cells.

As they found out how the brain transformed chemical stimuli into perception, their findings could change our entire approach, according to Columbia University Medical Center 

"Taste, the way you and I think of it, is ultimately in the brain," said study leader Charles Zuker, a professor of biochemistry and molecular biophysics and of neuroscience, a member of the Kavli Institute for Brain Science and the Mortimer B. Zuckerman Mind Brain Behavior Institute, and a Howard Hughes Medical Institute Investigator at Columbia University Medical Center (CUMC). "Dedicated taste receptors in the tongue detect sweet or bitter and so on, but it's the brain that affords meaning to these chemicals."

As every taste receptor is able to identify a different category of flavor, every class of receptors transmits a different signal to the brain. Hence, each taste is identified by diverse types of brain cells that are in diverse parts of the brain's cortex. All of them create a "map" of taste qualities.

With optogenetics the scientists could stimulate diverse neurons with a laser. Their aim was to manipulate the neurons in order to make the mice feel that they were tasting something either sweet or bitter, even though they were not exposed to either taste.

"In this study, we wanted to know if specific regions in the brain really represent sweet and bitter. If they do, silencing these regions would prevent the animal from tasting sweet or bitter, no matter how much we gave them," Zuker said. "And if we activate these fields, they should taste bitter or sweet, even though they're only getting plain water."

Hence, the scientists injected something into the mice to silence the sweet neurons, and found that the rodents could not identify sweet food, although they could find out bitter food. The opposite effect was achieved when the bitter neurons were blanked out.

Hence, the team could make the mice think that they were tasting something sweet or bitter even when they were just drinking water, and found that the mice could show increased or decreased licking or even gagging. Even when conducted on animals that had never tasted anything that was either sweet or bitter, the team found similar reactions.

"These experiments formally prove that the sense of taste is completely hardwired, independent of learning or experience," Zuker said. "Which is different from the olfactory system. Odors don't carry innate meaning until you associate them with experiences. One smell could be great for you and horrible to me."

Finally, the team trained mice to "perform a cue" when they tasted something that was bitter or sweet. They either fed them some food that had these qualities or made them believe they were tasting them. In both the situations, the mice's responses remained the same.

"In other words, taste is all in the brain," Zuker concluded.

The study was published in the journal Nature.

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