Circadian rhythms, aging and memory

In human beings and animal models, cognitive performance is often impaired in natural and experimental situations where circadian rhythms are disrupte d. This includes a general decline in cognitive ability and fragmentation o f behavioural rhythms in the aging population of numerous species. There is some evidence that rhythm disruption may lead directly to cognitive impair ment; however, this causal link has not been made for effects due to aging. We have tested this link by examining rhythms and performance on contextua l conditioning with the conditioned place preference task, in elderly, age- matched hamsters. Young healthy hamsters developed a preference for a conte xt that is paired with the opportunity to engage in wheel-running (experime nt 1). Aged animals with consolidated locomotor rhythms developed similar d egrees of preference, whereas the age-matched hamsters with fragmented rhyt hms did not (experiment 2). The degree of preference was also correlated wi th activity amplitude. These results support the notion that age-related rh ythm fragmentation contributes to the age-related memory decline. (C) 2000 Elsevier Science B.V. All rights reserved.