Participants in this research study have been determined to have approximately 24-hour (circadian) rhythms that are """"""""free-running."""""""" That is, they are not synthesized to the 24-hour day. Circadian rhythms are generated by an area of the brain, sometimes called the """"""""circadian clock."""""""" These rhythms include body temperature, sleepiness and the secretion of certain hormones. The circadian clock is ordinarily synchronized to the light-dark cycle; this is probably the reason that free-running (non 24-hour) circadian rhythms occur commonly in people who are totally blind. It has been assumed that the effect of light was completely mediated through the eyes; however, it has recently been reported that bright light exposure to the skin is able to reset the circadian clock in humans. The purpose of this study is to determine whether extraoccular light exposure can synchronize the circadian clock to a 24-hour cycle in totally blind people with free-running circadian rhythms. The light treatment will be for one week, but it may take up to six weeks to complete the entire study. We can tell the timing of the circadian clock by measuring the timing of melatonin secretion in hourly blood samples. In other words, melatonin can be thought of as the """"""""hands of the clock.
Showing the most recent 10 out of 336 publications
