Greater daytime sleepiness in subcortical stroke relative to Parkinson's disease and Alzheimer's disease.

Deficits in daytime alertness in the elderly may reflect, in part, deterioration of the critical neural systems modulating circadian control of sleep and wakefulness. In this study, 47 patients with subcortical stroke (n = 9), Alzheimer's disease (n = 6), and parkinsonism (n = 32) underwent a 24-hour in-laboratory evaluation consisting of overnight polysomnography and next-day evaluation of daytime sleep tendency with the Multiple Sleep Latency Test. Patients with stroke were significantly sleepier during the daytime relative to the Parkinson's and Alzheimer's disease patients. Nocturnal sleep parameters did not account for these differences. In the stroke patients, some infarcts occurred in the vasculature, impacting blood supply to the hypothalamus. We interpret these effects as representing functional interruptions of the suprachiasmatic nucleus (SCN). These results are also compatible with a wake-promoting function of the human SCN.