Figure 1.--

Recent research has fond that light on the back of the knees can affect a oerson's biologial clock. This may seem unbelievable, but just such research results have been reported by competent scientists. Researchers at this time have no exoplanation of this surprising research. This is a relatively new deveopment and not a known to parents in earlier years when boys more commonly wore short pants. Notably the shorts that many boys now wear or so long and baggy that they actually cover a boys knees except when he is sitting down--and then light does not get to the back of the jnees anyway.

Chronology

The research in question has been reported in the late 1990s. The first reserch results were reported in 1997.

Researchers

The first major study was published during 12997 in the journal Science. The work was cairred out by Dr. Scott Campbell and Dr. Patricia Murphy of the Laboratory of Human Chronobiology at Cornell University Medical College in White Plains, N.Y.

Human Master Clocks

Researchers believe that people possess a single master clock in the brain that "gives temporal organization to everything that we do," Campbell said, "but no one ever imagined we had light sensitive cells on any part of our bodies" outside of the eye. Even the eye, however, presents a mystery, he said. It contains special cells that gather light and enable vision. But these cells, called rods and cones, have nothing to do with resetting biological clocks. Interestingly, many blind people experience jet lag hust as sited people do. This suggestsg that other as yet undiscovered light sensitive cells in the eyes are sending important information about day length to the brain. Despite years of looking, no one has ever found such cells in the eye.

Research

"We thought we should look on the skin," Campbell said. An experiment done a decade earlier by Wehr had found that a couple of people with winter depression got better when light was administered to their face, arms, legs and not to the eyes, he said. "Dr. Wehr said it was so interesting that someone should someday repeat the experiment," Campbell said. "So we did."

Researchers had 15 volunteers came to the laboratory for four days and nights. On the first night, researchers determined each person's biological rhythm using two standard measures: body core temperature and the rise in a hormone called melatonin. "Your body temperature rises throughout the day and begins to declin around 7 or 8 o'clock at night," Campbell said. It falls to its lowest point about 5 or half past 5 in the morning and slowly starts to go up again. In a similar vein, melatonin begins to increase around 10 p.m. and makes people feel sleepy. It falls off again during the day.

On the third and fourth nights, all subjects were told to stay in bed from midnight to noon and were allowed to sleep as their biological rhythms were measured. In similar experiments done with light to the eyes, body clocks are unstable on the third day and this was also the case with light to the knees. The fourth day was a surprise. For those treated with light, the timing of their minimum body temperature shifted by up to 3 hours. Those getting the sham treatment experienced small but statistically insignificant changes in their bodily rhythms, Campbell said.

Results

Researchers report that somehow the impact has been in some unknown way tp reset the individuals master biological clock in the human brain. In one study, those treated with the light had their biological clocks advanced or delayed up to 3 hours.

Practical Consequences

The practical consequences of such a result could be used in long airplan flights. It could be used to counter the consequences of jet lag. Reserchers report that a dose of light behind the knees is enough to overcome the fatigue associated with familiar forms of jet lag or insomnia. Scientists believe that if these preliminary finding do hold up, they will have profound implications for basic biology, overturning conventional ideas of how biological clocks are set. It may also lead to new treatments for seasonal depression, sleep disorders and jet lag. Airline passengers could wear a knee brace with a light source that would reset their biological clocks as they slept during the flight.

The reported findings may have practical applications. People with winter depression often have to rise before dawn to look into a light source to alter their biological clocks, Campbell said. Now they might get the light treatment while they sleep. And, when flying to Paris, Campbell said, "With a light to the back of the knees, you could sleep while your clock is being shifted and wake up in the new time zone, ready to go."

Explanation

Why shining light on the knee would have this effect is not well understood by researchers, but some theories have been proposed. When life began, primitive creatures needed to have a way of keeping time and of knowing when it is light or dark, Campbell said. And so they evolved a variety of internal biological clocks--cells or clumps of cells that oscillate every 24 hours, sending out signals that control a host of behaviors such as when to wake up, go to sleep, eat, mate, hibernate and the like.

Some creatures have light sensitive cells on various parts of their bodies that help regulate the master clock. Horseshoe crabs have clock sensors on their tail, swallows have them just inside their skull and, according to a recent finding, fruit flies have time-keeping genes active in their legs, wings and hair bristles, suggesting that the entire body helps keep track of time. Because day length changes through the seasons, every animal theoretically has to reset its clocks every day.

Processes

"This is the first demonstration that you can affect the human clock without going through the eyes," Campbell said. "We assume that somehow a message is getting from the back of the knee to the master clock" in the brain.

How this happens is a major challenge to biologists. It could be via skin cells, which are sensitive to light. But how the message would get back to the brain is puzzling. Dr. Dan Oren, a researcher at the Yale School of Medicine in New Haven, Conn., recently suggested a daring hypothesis involving blood as a carrier of the light signal. Hemoglobin responds to light in much the same way that chlorophyll does in plants, Oren said, and chlorophyll regulates plant circadian rhythms. Moreover, hemoglobin carries nitric oxide, a neurotransmitter that could carry information about day length to the master clock in the brain.

The back of the knee happens to have many blood vessels but it is usually covered by clothing, Oren said. Another place rich in blood vessels is the retina. Thus the time sensitive cells that everyone has been looking for in the eye might not be cells at all; they could be hemoglobin molecules.

Validity

The finding is so surprising that many experts said they were withholding judgment until the experiment was done again. But those who heard the study described at a meeting during mid-2000 was carefully done. Respected reserchers have been surprised by the results reported, but do take them seriously despite their preliminary nature. "We were all flabbergasted," said Dr. Michael Menaker, a biologist at the University of Virginia in Charlottesville. "For 3 days we tried to find flaws in the experiment and we couldn't." Dr. Al Lewy, an expert on circadian rhythms at the University of Oregon Health Sciences University in Portland, said: "We've taken it as received wisdom that such effects would have to be mediated through the eyes. I am very surprised. It is so revolutionary." Dr. Thomas Wehr, chief of the clinical psychobiology branch at the National Institute of Mental Health in Bethesda, Md., said: "There are more biological mechanisms underlying the human response to light than was dreamt of in our original hypothesis. Still, until others repeat the experiment, the findings have to be regarded as preliminary."

Sources

Sandra Blakeslee, "Study Suggests Light to Back of the Knee Alters Master Biological Clock," N.Y. Times, January 16, 1998.

Created: October 13, 2000
Last updated: October 13, 2000