Differing molecular processes in an area of the brain is likely to play a significant role in the difference in intensity of jet lag, says a new study.
The human circadian clock operates on a period about 20 minutes longer than one day, which must be synchronized according to the light-dark cycle of the solar day, due to which someone whose clock runs faster than a solar day must delay it on a daily basis, and vice versa.
Although these daily adjustments happen naturally, yet the process is disrupted by sudden large shifts in the light-dark cycle because of a radically new geographic location.
The researchers, including a University of Washington biologist, exposed hamsters to two light-dark cycles, one of 23.33 hours and the other at 24.67 hours, to test the mechanisms that advance and delay the circadian clock.
A one-hour light pulse in the shorter cycle acted as dawn, but in the longer cycle it acted as dusk and the scientists confirmed that the pulse of light at dawn advanced the animals' circadian clocks, while the light at dusk delayed the clocks.
"We have known for decades that, in humans and other organisms, advances are always much harder to achieve than delays. For example, compare jet lag going to Europe with that coming back," Horacio de la Iglesia, a UW associate professor of biology, said.
"One of the reasons may be that these two forms of resetting the clock involve different molecular mechanisms at the clock level," he stated.
The results of the experiment suggest that different molecular mechanisms in the suprachiasmatic nucleus are at work when the circadian clocks are advanced than when the clocks are delayed.
The study has been published online in the Proceedings of the National Academy of Sciences.