NEWS AND VIEWS 11 March 2026 As mice age, changes in the microorganisms in their guts contribute to cognitive decline by altering signalling between the gut and brain. By Yi-Ting Cheng Yi-Ting Cheng is in the Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, 91125, USA. Sarkis K. Mazmanian Sarkis K. Mazmanian is in the Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, 91125, USA. Progressive decreases in the ability to learn and remember are a normal consequence of healthy ageing. Severe cognitive decline is also seen in ageing-associated conditions such as dementia. Writing in Nature , Cox et al . 1 present evidence that links ageing, changes in the population composition of microorganisms in the gut and cognitive decline. Nature 652 , 304-305 (2026) doi: https://doi.org/10.1038/d41586-026-00492-1 References Cox, T. O. et al. Nature 652 , 442–450 (2026).…