Daniel Foley, MS, National Institute on Aging, National Institutes of Health, Bethesda, MD.

Introduction
It is well known that sleep disturbances can occur secondary to the onset and progression of Alzheimer disease (AD) and related dementias in many patients.¹ In the community setting, sleep disturbances in AD patients can disrupt the sleep of caregivers and other family members and increase the risk of institutionalization.² In the institutional setting, sleep disturbances and other behavioural features known generally as "the sundown syndrome" present management problems for nurses and other attending staff in the late evening and at night.³

In contrast, few studies have reported on the possible neuropsychological deficits that may arise from disrupted sleep. However, because sleep complaints are common among elderly persons, clinical and epidemiological studies are now beginning to address the association between sleep disorders and cognitive function.⁴ Prevalence data show that a majority of older adults without dementia have one or more complaints, including difficulty initiating sleep, early morning awakening, daytime sleepiness and feeling unrested in the morning. These complaints may be attributable to underlying medical conditions that are common in old age such as hypertension, diabetes, depression and arthritis, or they may stem directly from the effects of common primary sleep disorders such as sleep-disordered breathing and restless leg syndrome.