Alterations in the circadian rest-activity rhythm in aging and Alzheimer's disease.

The suprachiasmatic nucleus, considered to be the endogenous circadian clock in the mammalian brain, shows morphological changes with aging, which become even more pronounced in Alzheimer's disease (AD). In order to assess possible functional implications of these alterations, circadian rest-activity rhythms of 6 young and 13 old volunteers and of 12 AD patients were studied with a recently developed ambulatory rest-activity monitor (RA24). Young and old volunteers showed no differences in their rest-activity rhythm in any of the variables studied. Comparison of old controls versus AD patients revealed that (1) rest-activity rhythm was markedly disturbed in many of the AD patients and tended to be correlated with the severity of the dementia; (2) disturbances were most pronounced in subjects using sedating drugs; (3) disturbances in the latter group did not result from medication as no differences were found in the rest-activity patterns before and after administration of sedating drugs; (4) negative findings reported in the literature concerning circadian disturbances in AD may well have resulted from selection criteria that excluded the group of patients with the most severely affected rest-activity rhythm; and (5) rest-activity monitors offer a practical and fruitful approach for the study of circadian rhythms in humans.