Can We Switch Off Our Sweet Tooth in Our Brains?

A study describes the complex brain circuitry that lets us identify, savor (or recoil from) a taste. (Credit: Pixabay)

Imagine how easy it would be to stick to a diet if we could rewire our brains so that tastes we usually crave became unpleasant. 

New research from a team led by neuroscientist Charles Zuker of Columbia University’s Zuckerman Institute suggest this may be possible. 

Their research in mice reveals that the brain’s underlying desire for sweet, and its distaste for bitter, can be erased by manipulating neurons in the amygdala, which is the emotion centre of the brain.

When removing an animal’s capacity to crave or despise a taste, it had no impact on its ability to identify it, the study showed. 

These findings, published in Nature, suggest that the brain’s complex taste system — which produces an array of thoughts, memories and emotions when tasting food — are actually discreet units that can be individually isolated, modified, or removed alltogether. 

“When our brain senses a taste it not only identify its quality, it choreographs a wonderful symphony of neural signals that link that experience to its context, hedonic value, memories, emotions, and the other senses, to produce a coherent response,” Dr. Zuker said. 

The study builds on previous work by Dr. Zuker and his team, to map the brain’s taste system. Previously, the researchers revealed that wen the tongue encounters one of the five tastes — sweet, bitter, salty, sour, or umami — specialised cells on the tongue send signals to specialised regions of the brain so as to identify he taste, and trigger the appropriate actions and behaviours. 

“Our earlier work revealed a clear divide between the sweet and bitter regions of the taste cortex,” said Li Wang, PhD, a postdoctoral research scientist in the Zuker lab and the paper’s first author. “This new study showed that same division continued all the way into the amygdala. This segregation between sweet and bitter regions in both the taste cortex and amygdala meant we could independently manipulate these brain regions and monitor any resulting changes in behavior.”

The scientists performed several experiments in which the sweet or bitter connections to the amygdala were artificially switched on, like flicking a series of light switches. When the sweet connections were turned on, the animals responded to water just as if it were sugar. And by manipulating the same types of connections, the researchers could even change the perceived quality of a taste, turning sweet into an aversive taste, or bitter into an attractive one.

In contrast, when the researchers instead turned off the amygdala connections but left the taste cortex untouched, the mice could still recognise and distinguish sweet from bitter, but now lacked the basic emotional reactions, like preference for sugar or aversion to bitter.

“It would be like taking a bite of your favorite chocolate cake but not deriving any enjoyment from doing so,” said Dr. Wang. “After a few bites, you may stop eating, whereas otherwise you would have scarfed it down.”

Usually, the identity of a food and the pleasure one feels when eating it are intertwined. But the researchers showed that these components can be isolated from each other, and then manipulated separately. 

In the immediate future, Drs. Zuker and Wang are investigating additional brain regions that serve critical roles in the taste system. For example, the taste cortex also links directly to regions involved in motor actions, learning and memory.

“Our goal is to piece together how those regions add meaning and context to taste,” said Dr. Wang. “We hope our investigations will help to decipher how the brain processes sensory information and brings richness to our sensory experiences.”