A new study published in the journal Nature Neuroscience reveals that sugar stimulates two different parts of one brain region in order to encourage you to eat more. By creating a desire for both its high calorie content and the need to taste something sweet, sugar proves to be virtually irresistible. However, it is the need for calories that appears more important than the desire for sweetness.
Anything that gives us an incredibly rewarding feeling, one that makes us want to repeat the procedure that generated it, is known as a reinforcing mechanism. It’s well-established that sugar causes the release of significant levels of dopamine, a neurotransmitter that plays a role in reward-motivated behaviors, within the brain. It’s this dopamine release that ensures that sugar’s reinforcing mechanism is potent, to say the least.
For this new study, a team of researchers decided to investigate if the rewarding feeling of both tasting sweetness and obtaining a lot of calories from sugar originates from the same region of the brain. By carefully observing 170 laboratory mice as they encountered a range of sugary treats and artificial sweeteners, and monitoring their brains’ dopamine production and electrical activity, they hoped to find an answer.
They found that both the sweet taste and the nutrient value of sugar register in the striatum, an ancient region of the brain that evolved before many other components, and one generally linked to rewarding behaviors. However, the team noted that two different parts of the striatum separately registered the sweetness and the high calorie content.
The ventral striatum generated the sweetness reward, whereas the dorsal striatum was found to be associated with the calorific reward. The former is part of the brain’s reward system, whereas the latter is more commonly linked to parts of the brain that activates motor behavior – essentially, the ability to physically respond to external stimuli by moving parts of the body.
The striatum (red) within the brain, imaged using an MRI scanner. Lindsay Hanford, Geoff B Hall/Wikimedia Commons; CCO
This shows that the part of the brain normally linked to motor behavior has an additional role in generating new behaviors as well as reinforcing them, specifically in response to rewards found in the environment.
Remarkably, the dorsal striatum had the ability to override the primarily reward-focused ventral striatum. When the researchers laced a sugary drink with a bitter, disgusting-tasting chemical, and then used focused light to stimulate cells within the dorsal striatum, the mice actually licked more of it than the tasty, calorie-free artificial sweetener. This shows that their brains prioritize the high calorie content of sugar far more than the taste of something sweet.
“We show that this area [of the brain] basically commands the behavior of the animal,” said senior author Ivan de Araujo, an associate fellow at the Yale University-affiliated John B. Pierce Laboratory in New Haven, Connecticut, and co-author of the study, according to TIME Magazine. The dominance of the dorsal striatum “allows the animal to disregard any aversions in order to prioritize energy-seeking.”
In order to confirm this finding, the researchers surgically removed the dopamine-responsive parts of the dorsal striatum from the mice. When the experiment was repeated, they only went for the artificial sweetener, not the bad-tasting sugar, indicating that the ventral striatum was now the commanding reward force in the brain.