A bad experience with a particular food triggers future aversion to that taste by depressing the activity of a group of brain cells, shows a study published today in eLife.
The results may help explain how a single bad experience, such as a bout of food poisoning after eating a particular food, changes the way a person or animal perceives the taste of that food. They also show that reduced activity in certain brain cells can contribute to avoiding the food.
Learning to avoid foods that cause harm is essential to survival. Scientists know that parts of the brain responsible for taste and for recognising threats are involved, but how the brain learns to associate a particular taste with a threat is unclear.
To find out more, Melissa Haley, a postdoctoral fellow in the Maffei lab at Stony Brook University, New York, US, studied rats that were conditioned to dislike the taste of sugar water. Haley and the team looked at the changes that occurred in the threat-sensing and taste centers of the brain.
Their experiments showed that the expression of genes associated with learning was reduced in the sugar-averse animals. Additionally, the connection between the threat-sensing brain cells and the taste-sensing brain cells was weakened.
The team then used a technique called optogenetics, which involves using light to control the activity of brain cells, to study these changes in the rat brain following conditioned taste aversion. They used the technique to artificially reduce the activity between the threat-sensing and taste-sensing brain cells, and found that this could cause normal rats to develop a taste aversion to sugar water.
“Our experiments provide the first direct evidence that learning to avoid certain tastes depends on the long-term reduction of activity in connections between the taste and threat sensors in the brain,” Haley says.
The findings also suggest that reducing activity between two brain centres can be an important way in which animals learn other behaviours, adding to our understanding of the processes that enable learning and lead to changes in behaviours. “This discovery could have important implications for helping people break addictions to harmful substances,” Haley adds.
Senior author Arianna Maffei, Professor at the Department of Neurobiology & Behavior, Stony Brook University, concludes: “Our results link reduced communication between the taste and threat-processing centres to a change in taste preference. This shows that changes in communication between brain centres can influence the way animals perceive and behave toward things that make them feel good or bad.”
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