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Abstract
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.