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Before 2 p.m. EST Thursday, February 7, 2002

News Service Contact: Scott Turner



Mary Carskadon

Berson’s findings are important in understanding this vital system

Mary Carskadon, an internationally recognized researcher in the biology of sleep and circadian rhythms, comments on the discovery by David Berson and colleagues of a third light-transducing cell in the eye. Carskadon is professor of psychiatry and human behavior at Brown University. The research is reported in the Feb. 8, 2002, issue of Science.


Scientists have known for a long time that there is a direct neural pathway between the retina and the clock (the suprachiasmatic nucleus of the hypothalamus, or SCN). It was thought that some folks who were blind, yet able to synchronize their clocks, had damage somewhere else in the visual system beyond this tract, such as in the visual cortex.

Assuming that this system is actually involved in resetting the clock, the finding is important in providing another link in understanding this vital system. Virtually every one of our biological processes has a daily rhythm, and it is the SCN that synchronizes these rhythms using light as the major signal.

Even in humans, light input is crucial. By identifying the key light-receiving cells, we can learn more clearly how the system is put together, since scientists can be looking at the correct machinery. Questions about the critical features of light input (e.g., wave length, brightness, length of exposure) required to reset the clock and so forth might be better addressed by examining the properties of this cell type rather than rods and cones. Furthermore, for people who have trouble resetting their clocks, a better understanding of this critical step in the synchronizing mechanism may lead to clinical interventions. Thus, for example, a certain neurotransmitter or enzyme or other process that might not be relevant for the vision aspects of the visual system could now be identified as important.

Ultimately, a full understanding of the light-transducing mechanism has the potential to provide insights that may help humans work more congenially with the brain’s 24-hour clock and may lead to interventions to improve defects in the system. The more scientists know about a system, the more they are able to figure out how it fails and how to correct failures.

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