Scientists trace the nerve pathway that links digestion to memory
A new small study in rats reveals that the digestive tract communicates with the brain during meals to help remember where food was found, a process that can be disrupted by an early-life junk food diet.
A recent study published in Nature Communications has uncovered a nerve pathway linking digestion to memory in rats. The research, conducted by scientists at the University of Southern California, reveals that nutrients consumed during meals trigger a nerve pathway that releases a memory-boosting chemical in the brain. This process, which involves the vagus nerve acting as an information highway, can be disrupted by a diet high in junk food during early life.
The vagus nerve transmits metabolic data from the gastrointestinal tract to the central nervous system, influencing energy balance and food intake. Sensory neurons within the vagus nerve may send messages to the hippocampus, a brain structure responsible for spatial navigation and forming episodic memories. In their study, researchers injected male rats with a hormone called cholecystokinin, which is released by the intestines during digestion and makes animals feel full.
They found that this hormone triggered a surge of cellular activity and acetylcholine release in the hippocampus. By destroying a specific group of cells in the medial septum, a region that connects lower brainstem regions to the hippocampus, the researchers demonstrated that this relay station is necessary for the gut hormone to trigger acetylcholine release.
Experiments with different liquids showed that only calorie-rich sugar and fat solutions caused the acetylcholine spike in the hippocampus, indicating that the brain is reacting to the presence of actual nutrients rather than just the taste or physical act of swallowing. Severing the vagus nerve in rats eliminated the acetylcholine spikes in response to the gut hormone and regular meal consumption.
Rats with severed vagus nerves also showed fewer transport proteins needed to package and release acetylcholine in the hippocampus. Furthermore, rats fed a junk food diet during early development lost the ability to maintain a post-meal acetylcholine spike and struggled with memory tasks, such as navigating a maze to find food. These findings suggest that a highly processed diet during early life can cause long-lasting damage to nerve pathways, impairing memory formation and retrieval.
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