Signals traveling from the gut through the vagus nerve may play a role in memory formation, according to research led by Scott Kanoski, professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences. The findings were published in Nature Communications and announced on July 27.
The study focused on how communication between the digestive system and brain via the vagus nerve influences memory. Researchers found that when rats consumed nutritious foods, neurons communicating with the hippocampus released higher levels of acetylcholine, a neurotransmitter that supports memory formation. This response depended on signals traveling from the gut through the vagus nerve; when this communication was interrupted, acetylcholine release decreased and rats performed worse on memory tests involving food location.
Researchers also observed that brain responses were linked to a food's nutritional value rather than just its taste. Rats given sugar or fat showed strong memory-related brain activity, while those given sweet-tasting but low-calorie liquids did not display similar responses. Study first author Logan Lauer said, "We think the mechanism likely evolved to help animals remember vital information about food sources." Lauer added that signals from the gut tell the brain, "This meal provided valuable nutrients, so remember where and how you got it."
However, chronic exposure to high-fat and high-sugar diets early in life weakened communication between the gut and hippocampus over time. Even after switching back to healthier diets, affected rats continued to show reduced memory-related responses in their brains.
The researchers noted these findings could have implications for human health because obesity and metabolic disorders are associated with cognitive decline. The study suggests constant exposure to junk foods might disrupt connections between gut and brain. The authors indicated further research is needed to determine if similar mechanisms exist in humans.
Other contributors included 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; Léa Décarie-Spain of Université de Montréal.
