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. Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any time Subscribe to this journal Receive 51 print issues and online access $199.00 per year only $3.90 per issue Rent or buy this article Prices vary by article type from$1.95 to$39.95 Prices may be subject to local taxes which are calculated during checkout doi: https://doi.org/10.1038/d41586-026-00492-1 Cox, T. O. et al. Nature https://doi.org/10.1038/s41586-026-10191-6 (2026). Article Google Scholar Yassa, M. A., Mattfeld, A. T., Stark, S. M. & Stark, C. E. L. Proc. Natl Acad. Sci. USA 108, 8873–8878 (2011).…