Signals from the intestines control brain youth

Traditionally, there are five main senses, but there is also interoception — the brain’s ability to subconsciously perceive the state of internal organs. The main channel of this connection is the vagus nerve, which connects the intestine to the brain and transmits the data necessary for the regulation of cognitive functions. The study showed that it is the signals from the digestive system to the brain that protect the body from memory loss. With age, this connection is disrupted due to a decrease in interoceptive sensitivity, however, stimulation of certain sensory neurons in the intestine allowed old mice to regain cognitive functions at the level of young individuals.

The key factor in these changes was the aging microbiome. To test its impact on the brain, scientists transplanted the microbiome of older mice into younger mice, and the younger mice began to show memory impairment. The main culprit was the bacterium Parabacteroides goldsteinii. The memory blockage mechanism is triggered when the aging microbiome produces an excess of medium-chain fatty acids. These molecules activate immune cells in the gut, which in turn release the pro-inflammatory molecule IL-1β. This substance suppresses the sensory neurons of the vagus nerve, preventing critical signals from reaching the hippocampus, the center of memory formation in the brain.

The most encouraging result of the study was the proven reversibility of the process. The researchers successfully tested several methods for restoring memory in mice, including the use of bacteriophages to suppress harmful microbes and direct stimulation of the vagus nerve. This was achieved using GLP-1 receptor agonists, which are similar to modern weight-loss medications. These interventions completely eliminated age-related memory deficits in the experimental animals.

Although the study was conducted on mice, scientists see great potential for future medicine. It is already known that people undergoing vagus nerve stimulation in the treatment of epilepsy often report improved memory. This discovery proves that the processes we are used to calling brain aging can be controlled and corrected outside the skull – through manipulation of the intestines and its microflora.