A new study of the brain's master circadian clock known as the suprachiasmatic nucleus, or SCN reveals that a key pattern of rhythmic neural activity begins to decline by middle age. The study, whose senior author is UCLA Chancellor Gene Block, may have implications for the large number of older people who have difficulty sleeping and adjusting to time changes.
"Aging has a profound effect on circadian timing," said Block, a professor of psychiatry and biobehavioral sciences and of physiological science. "It is very clear that animals' circadian systems begin to deteriorate as they age, and humans have enormous problems with the quality of their sleep as they age, difficulty adjusting to time-zone changes and difficulty performing shift-work, as well as less alertness when awake. There is a real change in the sleepwake cycle.
"The question is, what changes in the nervous system underlie all of that? This paper suggests a primary cause of at least some of these changes is a reduction in the amplitude of the rhythmic signals from the SCN."
The SCN, located in the hypothalamus, is the central circadian clock in humans and other mammals and controls not only the timing of the sleepwake cycle but also many other rhythmic and non-rhythmic processes in the body.
The UCLA research team examined the SCN in mice and found that while critical neural activity rhythms were already disrupted in middle age, the molecular mechanisms that generate these rhythms were not significantly altered.
"These results indicate that the outputs of the central circadian clock start to decline in middle age and suggest that the same may be true in humans," said study co-author Christopher Colwell, a UCLA professor of psychiatry and biobehavioral sciences who has conducted research with Block for many years. "Before this study, we did not know that the SCN was the site where the decline occurs."
In a technical tour de force, th
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University of California - Los Angeles