Does deterioration of the gut microbiome age the brain? Transplanting gut bacteria from old mice impairs memory in young mice, study published in Nature: Innovative Tech

Nature paper links age-related gut dysfunction to cognitive decline in mice.

Transplanting or co-housing with aged mice altered young mice's gut microbiota and reduced hippocampal function and memory (both sexes).

Young-to-young co-housing did not impair memory; germ-free co-housing prevented decline, implicating microbiota rather than social factors.

Specific bacteria (e.g., Parabacteroides goldsteinii) increased with age, overproducing medium-chain fatty acids that activate GPR84 on immune cells, trigger inflammation, suppress vagus nerve signaling, and weaken hippocampal stimulation.

Impairment was reversible; reducing gut-derived medium-chain fatty acids led to recovery of function.