A madeleine dipped in tea famously transported French writer Marcel Proust back to vivid childhood memories. New research suggests that food-related memories may involve more than the brain alone. Signals sent from the digestive system could help determine which experiences involving food are stored as long-term memories.
A study led by Scott Kanoski, professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences, suggests that the gut may play an important role in memory formation, especially when an experience involves locating and eating food.
Published in Nature Communications, the research focused on the vagus nerve, a major communication pathway connecting the digestive system and the brain. Although the vagus nerve is already known to influence digestion, appetite, and feelings of fullness, the new findings suggest that it may also transmit signals that help the brain create and store memories.
How Gut Signals Influence Memory
In experiments involving rats, researchers found that eating nutrient-rich food increased the release of acetylcholine in neurons connected to the hippocampus. This brain region plays a central role in learning, memory, and spatial navigation.
Acetylcholine is a neurotransmitter that helps the brain process new information and form memories. According to the study, the increase in acetylcholine depended on signals traveling from the gut to the brain through the vagus nerve.
When researchers interrupted communication along the vagus nerve, acetylcholine levels did not increase after the rats ate. The animals also performed worse on memory tests that required them to remember where they had recently found food.
Nutrients May Matter More Than Taste
The experiments showed that the brain’s memory system responded to the nutritional value of food rather than simply to its sweetness or pleasant taste.
Rats that consumed sugar or fat showed strong activity in brain pathways associated with memory. However, rats given low-calorie or noncaloric liquids with a sweet taste did not show the same response.
These findings suggest that the brain can distinguish between flavor and nutrition. Sweetness alone was not enough to activate the gut-brain pathway linked to food-related memory.
“We think the mechanism likely evolved to help animals remember vital information about food sources,” says study first author Logan Lauer, a PhD student in Kanoski’s lab. Remembering where nutritious plants grow, for example, could help animals locate essential food during times of scarcity. Signals from the gut may tell the brain, “This meal provided valuable nutrients, so remember where and how you found it.”
Why Food-Location Memories Are Important
For animals living in the wild, remembering the location of a dependable food source can be critical for survival. When a meal provides valuable nutrients, signals from the digestive system may encourage the brain to store information about where the food was found and how it was obtained.
This gut-to-brain process could help explain why some eating experiences become especially memorable. The body may prioritize memories connected to foods that provide energy and essential nutrients.
Unhealthy Diets May Disrupt the Gut-Brain Memory Pathway
Although sugar- and fat-rich foods produced strong short-term memory responses, frequent exposure to these foods appeared to have negative effects over time.
Rats that consumed high-fat and high-sugar diets early in life later showed weaker communication between the gut and the hippocampus. Their memory-related brain activity remained reduced even after they returned to a healthier diet.
The animals also performed worse on tasks that tested their ability to remember where food had been located. The findings suggest that long-term consumption of unhealthy foods may interfere with the gut-to-brain communication system that helps create food-related memories.
Potential Connections to Cognitive Decline
The study may have broader implications for human health. Obesity, poor nutrition, and metabolic conditions such as diabetes have been associated with an increased risk of cognitive decline.
The research points to one possible biological explanation: repeated exposure to unhealthy foods may disrupt communication between the gut and the brain, making it more difficult for memory systems to function normally.
The findings may also provide clues about neurodegenerative diseases, including Alzheimer’s disease.
“The disruption of acetylcholine signaling in the hippocampus is one of the earliest neurochemical changes in Alzheimer’s disease,” says Kanoski. “By revealing that this system is boosted by gut signaling from the vagus nerve, novel therapeutic targets could leverage this information to explore vagus nerve-based approaches, such as vagus nerve stimulation.”
Could Vagus Nerve Stimulation Support Memory?
The discovery raises the possibility that future treatments could focus on improving communication between the digestive system and the brain.
Therapies designed to stimulate the vagus nerve or support gut health may eventually be investigated as potential ways to protect memory and cognitive function. Vagus nerve stimulation is already being studied for several neurological and psychiatric conditions, and these findings suggest that memory could become another area of interest.
Researchers caution that additional studies are needed to determine whether the same gut-brain memory process occurs in humans. For now, the findings add to growing evidence that the digestive system and the brain work together more closely than previously understood.
About the Study
In addition to Kanoski and Lauer, the study’s authors include Anna Hayes, Andrea Suarez, Alexander Bashaw, Molly Klug, Alicia Kao, Robert Cheng, Jessica Rea, Keshav Subramanian, Anna Nourbash, Kristen Donohue, and Lindsey Schier of USC Dornsife; Kevin Myers of Bucknell University; and Léa Décarie-Spain of Université de Montréal.
The research was supported by National Institute of Diabetes and Digestive and Kidney Diseases grants DK104897, DK123423, and F31AG092136; a Postdoctoral Ruth L. Kirschstein National Research Service Award from the National Institute on Aging, grant F32AG077932; Quebec Research Funds postdoctoral fellowship 315201; and an Alzheimer’s Association Research Fellowship to Promote Diversity.
Source: www.sciencedaily.com