Lynn Hasher, PhD
David Goldstein, PhD
Baycrest Centre for Geriatric
Care and University of Toronto,
A variety of important biological, physiological and psychological functions show regular peaks and declines across 24-hour cycles. Such rhythms are present in plants and animals, from the cellular level to the level of organs and even entire organisms.1 The characteristics and implications of these circadian rhythms have been the focus of a growing body of literature in the fields of chronobiology, chronopathology and chronotherapy. For example, because of underlying circadian rhythms in cortisol concentration in the blood stream, histamine, epinephrine, pulse rate, blood pressure and clotting factors, treatment efficacy varies with the time of administration for diseases such as arthritis, asthma, cancer and cardiovascular disease.2-5 Recent work in the newly emerging area of chronocognition also shows that behavioural efficacy varies depending on the time of administration of tasks.6 Of special relevance is the clear suggestion of age differences in circadian arousal patterns, differences that raise a number of important issues for both research and clinical practice, including what patients are likely to understand and remember from a medical appointment.