Department of Neuropsychiatry
Akita University School of Medicine
ncreased daytime napping, early morning awakening, frequent nocturnal sleep interruptions, and lowered amplitude and phase advance of the circadian sleep-wake rhythm are characteristic features of sleep-waking and chronobiological changes associated with aging. The chronobiological changes are probably caused by one or more of the following factors: 1) functional and/or organic deterioration of the suprachiasmatic nucleus which is believed to be the center of the mammalian circadian time keeping system (disturbed oscillation), 2) decreased exposure to time cues due to environmental causes, such as social isolation (disturbed entrainment), 3) lowered sensitivity of sensory organs to time cues due to physical and mental disorders (disturbed entrainment), and 4) reduced ability of peripheral effector-organs to express circadian rhythms (disturbed manifestation). Especially in elderly patients with dementia, severely fragmented sleep-waking patterns are frequently observed, being associated with circadian rhythm disorder of other physical functions, such as autonomic and endocrine functions. For example, disorganized body temperature rhythm and suppressed nocturnal melatonin secretion are often observed in patients with multi-infarct dementia. In addition, institutionalization for taking care of such elderly patients often causes further exacerbation of their circadian rhythm disorders through insufficient "social interaction" and reduced "environmental light" in the daytime, both of which act as strong synchronizers for the human circadian time keeping system. Recent researches have disclosed that increased social interaction and intensification of environmental light in the daytime, and supplementary administration of melatonin exhibit favorable effects on disturbed circadian rhythms among institutionalized elderly patients with dementia. Both bright light and melatonin appear to modulate directly various physical and mental functions including autonomic, thermoregulating, and sleep-waking functions, in addition to their phase shifting action on circadian rhythms. These indicate that bright light and melatonin are potent therapeutic means for the disturbed sleep-wake rhythm in demented elderly patients. It is important to find most effective therapeutic design and most suitable type of diseases associated with dementia for using bright light and melatonin.
