Microbes Can Exacerbate Cognitive Decline

Researchers recently found that gut microbes can exacerbate the effects of cognitive impairment because of how they affect the hippocampus, the region of the brain that is critical for memory and learning. They found that the concentration of one group of bacteria called Bilophila increased dramatically in the gut microbiota of mice that were fed a ketogenic diet and were intermittently deprived of oxygen, creating a condition called hypoxia.

The researchers gave several mice a ketogenic diet and others a standard diet. Then, all of the mice received reduced levels of oxygen for five consecutive days and then were given four days to recover. 

Next, the scientists observed their ability to navigate a maze. When trying to find their way out of a maze, mice on the ketogenic diet made an average of 30% more errors than mice given the standard diet.

The researchers also investigated what would happen if they depleted the mice’s microbiota before administering a ketogenic diet and exposing them to hypoxia. Interestingly, mice that had their microbiota depleted first made significantly fewer errors in the maze than mice that were exposed to hypoxia and given a ketogenic diet but had not had changes to their microbiota first.

“This suggests that the microbes associated with the ketogenic diet and hypoxia could contribute to the detrimental effects on cognitive impairment,” Olson said.

The authors determined that Bilophila wadsworthia changes which genes are turned on or off in the hippocampus, and that the bacterium reduces normal cellular signaling in the hippocampus.

“Bilophila wadsworthia disrupted hippocampal activity and cognitive behavior in ways similar to how hypoxia and the ketogenic diet together did,” Olson said. 

“Identifying early risk factors is critical to enabling early detection and interventions for cognitive impairment,” said Hsiao, the paper’s senior author.

Hsiao added that more research is needed to determine whether other gut microbes besides Bilophila might also affect cognitive ability and whether the microbiota could influence cognitive decline in humans.


Christine A. Olson, Alonso J. Iñiguez, Grace E. Yang, Ping Fang, Geoffrey N. Pronovost, Kelly G. Jameson, Tomiko K. Rendon, Jorge Paramo, Jacob T. Barlow, Rustem F. Ismagilov, Elaine Y. Hsiao. Alterations in the gut microbiota contribute to cognitive impairment induced by the ketogenic diet and hypoxia. Cell Host & Microbe, 2021; DOI: 10.1016/j.chom.2021.07.004

University of California – Los Angeles. “How microbes can exacerbate cognitive decline.” ScienceDaily. ScienceDaily, 17 August 2021. <www.sciencedaily.com/releases/2021/08/210817131335.htm>.

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