Signals from the digestive system help the brain remember which tastes are associated with the intake of nutrients. Researchers at the University of California, San Francisco, and their colleagues have described the dopamine pathway involved in this learning process. The study was published in the journal Nature.
Unlike the brain's rapid response to the sight or taste of food, this signal develops after food enters the gastrointestinal tract. It allows the brain to link taste sensations with what the body actually receives from food.
In experiments, mice were given nutrient solutions directly into their stomachs, separating the effects of nutrients from those of taste. The researchers detected sustained dopamine release in a small region of the anterior basolateral amygdala, a brain area involved in learning and processing emotionally significant information.
When this pathway was disrupted, the animals continued eating but stopped learning to prefer tastes associated with calorie intake. The opposite intervention produced the reverse effect: artificially activating dopamine fibres created a taste preference even in the absence of nutritional reinforcement.
The response was predominantly observed on the left side of the brain. An additional analysis of human studies also revealed a response in the corresponding brain region following nutrient intake.
This mechanism may help explain why foods that initially seem unfamiliar can become more appealing over time. The authors cite bitter coffee as a possible example of this type of learning, although the development of a liking for coffee itself was not tested in the experiment. Practical ways of changing food preferences by targeting this pathway have yet to be developed.
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