French writer Marcel Proust famously recalled the vivid memories of his childhood when he heard the taste of madeleines. New research suggests there may be more to this type of reminiscence than just the brain. Signals from the digestive system may also help determine which food-related experiences become memories.
The study, led by Scott Kanosky, a professor of biology in the USC Dornsif College of Letters, Arts and Sciences, shows that the gut may contribute to memory formation, especially when it comes to the experience of finding and consuming food.
Published in nature communicationsthe study looked at the vagus nerve, one of the body’s main communication pathways between the digestive system and the brain. Nerves are already known to influence digestion, appetite, and satiety. New findings suggest that the brain may also carry information that helps us store memories.
How intestinal signals reach memory centers
In experiments with rats, researchers found that eating nutrient-rich foods increased the release of acetylcholine in neurons connected to the hippocampus. The hippocampus is a region of the brain that plays a central role in learning and memory.
Acetylcholine is a neurotransmitter that helps the brain record new information and form memories. This increase depended on messages traveling from the intestine through the vagus nerve.
When the researchers blocked communication along the vagus nerve, acetylcholine levels no longer rose after the animals ate. The rats also struggled more on tests that required them to remember where they had recently found food.
Nutrients are more important than sweetness
The experiment also showed that the brain’s memory system responds not just to the taste or sweetness of food, but also to the nutritional content of the food.
Rats that consumed sugar and fat showed stronger activity in brain pathways involved in memory. In contrast, animals given sweet-tasting low- or non-caloric liquids did not have the same response.
This result suggests that the brain distinguishes between taste and actual nutritional value. Sweet taste alone was not enough to activate memory-related pathways.
“This mechanism likely evolved to allow animals to remember important information about food sources,” says study lead author Logan Lauer, a doctoral student in Kanosky’s lab. Remembering where certain plants first sprout in the spring can help hungry animals find important nutrients. Signals from the gut tell the brain, “This meal contains valuable nutrients, so remember where and how you took it.”
Why memory of food location is important
For animals in the wild, remembering the location of reliable food sources is essential to survival. A diet that provides useful nutrients can cause your gut to send messages that prompt your brain to remember details about where that food was found and how it was obtained.
This process may help explain why certain food experiences are particularly memorable. Your body may be designed to place more emphasis on foods that deliver energy and valuable nutrients.
Unhealthy diet can weaken the pathway
Foods rich in sugar and fat triggered strong short-term memory responses, but frequent exposure to these foods had the opposite effect over time.
Rats that ate high-fat and high-carbohydrate diets early in life were shown to have weaker communication between the gut and hippocampus later in life. Their memory-related brain responses remained reduced even after returning to a healthier diet.
These animals also performed poorly on tasks that tested their ability to remember where food was. The results suggest that long-term consumption of unhealthy foods may interfere with the gut-to-brain system that helps record food-related memories in the first place.
Possible association with cognitive decline
This discovery could have broader implications for human health. Metabolic disorders such as obesity, malnutrition, and diabetes are already associated with an increased risk of cognitive decline.
This study points to one possible biological explanation. Repeated exposure to unhealthy foods gradually damages or disrupts communication between the gut and the brain, making it difficult for the memory system to function properly.
The results may also provide clues about neurodegenerative diseases.
“Disruption of acetylcholine signaling in the hippocampus is one of the earliest neurochemical changes in Alzheimer’s disease,” says Dr. Kanosky. “By revealing that this system is facilitated by intestinal signaling from the vagus nerve, new therapeutic targets could leverage this information to explore vagus nerve-based approaches such as vagus nerve stimulation.”
New possibilities for memory treatment
This finding raises the possibility that future treatments will focus on strengthening communication between the digestive system and the brain.
Approaches that stimulate the vagus nerve or improve gut health may eventually be investigated as ways to support memory and preserve cognitive function. Vagus nerve stimulation has already been studied for several neurological and psychiatric conditions, and new findings suggest that memory may be another area of interest.
The researchers caution that further research is needed to determine whether the same process occurs in humans. So far, the experiment provides further evidence that the gut and brain are much more closely linked than once thought.
About research
In addition to Kanosky and Lauer, study authors include Anna Hayes, Andrea Suarez, Alexander Bashaw, Molly Klug, Alicia Cao, Robert Chen, Jessica Rea, Keshav Subramanian, Anna Nuavash, Kristen Donahue, and Lindsay Shea of Dornsaif University of Southern California. Kevin Myers of Bucknell University. Léa Decary España of the University of Montreal.
This research was supported by National Institute of Diabetes and Digestive and Kidney Diseases grants DK104897, DK123423, and F31AG092136. Postdoctoral Researcher Ruth L. Kirschstein received a National Research Service Award from the National Institute on Aging Grant F32AG077932. Quebec Research Fund Postdoctoral Fellowship 315201; and the Alzheimer’s Association Research Fellowship to Promote Diversity.
