New research on taste aversion clarifies how a stomachache can turn a food from must-have to must-avoid.
The study, published in eLife, involved conditioning rats to dislike the taste of sugar water, something they would normally enjoy, by creating a mild digestive discomfort after they consumed it.
A powerful memory forms when a pleasant taste is associated gastrointestinal pain, similar to an experience with food poisoning that results in an aversion to that food. Scientists have debated how the brain works in this process to form a long-lasting memory.
According to Arianna Maffei, senior author and professor in the neurobiology and behavior department at Stony Brook University, the areas of the brain involved in this form or learning—the basolateral amygdala and the portion of the insular cortex involved in taste processing (gustatory cortex) have been known for some time, but there is no clear understanding of how they may work together during learning.
Maffei, Melissa Haley, a postdoctoral fellow in the Maffei Lab, and colleagues investigated the neural mechanisms behind the taste aversion response. They used optogenetics, a technique that combines light and genetic information to control neurons in the brain and recorded behavioral reactions and neural pathways involved in taste and threat.
They discovered that conditioned taste aversion learning decreases the strength of the synaptic connection between basolateral amygdala and gustatory cortex and leads to an overall decreased activation of neurons in the gustatory cortex—a different process from the widely accepted idea that to form a memory, neurons need to be active at the same time.
“Our experiments provide the first direct evidence that learning to avoid certain tastes depends on the long-term reduction in the activity in connections between taste and threat sensors in the brain,” Haley says.
“The findings also suggest reducing the activity between two brain centers can be an important way in which animals learn other behaviors, which adds to our understanding of the processes that enable the formation of memories and lead to changes in behavior.”
“These results link reduced communication between the taste and threat-processing centers to a change in taste preference and shows that changes in communication between brain centers can influence the way animals perceive and behave toward things that make them feel good or bad,” Maffei says.
Both Haley and Maffei emphasize that the discovery could have broader implications in the area of neurobiology intervention for helping people to break addictions to harmful substances. They say additional research may provide further evidence on how these regions of the brain work toward taste and other related aversions.
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