Our cognitive powers peak in autumn Andrey Bandurenko / Alamy

Human cognitive powers have a seasonal rhythm, and for those living in temperate regions in the northern hemisphere they are strongest in late summer and early autumn. The effect is large enough to tip some older people over the diagnostic threshold for dementia if their cognitive tests are carried out in winter or spring.

Andrew Lim, a neurologist at the Sunnybrook Health Sciences Centre at the University of Toronto, and his colleagues analysed data from 3500 participants aged 60 or over. All of them had undergone tests of their thinking …