A new Yale study shows the brain responds to taste and calorie counts in fundamentally different ways. And only one of these responses explains why most New Years’ resolutions have already disappeared under a deluge of Boston Crème Pies. It’s the brain’s desire for calories – not sweetness – that dominates our desire for sugars.
“It turns out the brain actually has two segregated sets of neurons to process sweetness and energy signals,” said Ivan de Araujo of the John B. Pierce Laboratory. “If the brain is given the choice between pleasant taste and no energy, or unpleasant taste and energy, the brain picks energy.”
Both sweet taste and nutrient value register in the striatum, an ancient region of the brain involved in processing rewards. Humans have a sweet tooth as one way to ensure we eat enough to give our large brains enough calories to operate at peak efficiency. However, the Yale team studying the brains of mice showed signals for taste and nutrients are processed in 2 separate areas of the striatum, the ventral and dorsal, respectively. Signals about the value of taste are processed in the ventral striatum while nutritional value was processed in the dorsal striatum. The dorsal striatum remained responsive to energy even when calories fed to mice were paired with a very aversive taste.
Mice fed both sugar with sweet taste but no calories or sugar that contained calories but was altered to taste horribly preferred the sugar with energy. When neurons in dorsal striatum were activated by optogenetics, mice also ate copious amounts of bad-tasting sugar.
During sugar intake, suppressing hedonic value inhibited dopamine release in ventral, but not dorsal, striatum, whereas suppressing nutritional value inhibited dopamine release in dorsal, but not ventral, striatum. Ablation of dopamine-excitable cells in dorsal, but not ventral, striatum inhibited sugar’s ability to drive the ingestion of unpalatable solutions. Conversely, optogenetic stimulation of dopamine-excitable cells in dorsal, but not ventral, striatum substituted for sugar in its ability to drive the ingestion of unpalatable solutions. ie Sugar recruits a distributed dopamine-excitable striatal circuitry that acts to prioritize energy-seeking over taste quality. The authors hope findings help spur new strategies aiming at curbing excess sugar intake. http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.4224.html http://news.yale.edu/2016/01/25/yale-team-deciphers-sugar-s-siren-song
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