Jet-lagged travelers who can no longer tell what time it is may be tuning in to a confusion rooted deep in their biology. The brain contains at least two separate internal clocks that can fall out of sync; when that happens, the result is that sleepless, disoriented feeling that long-distance travelers know only too well.
As is often the case, Horacio de la Iglesia of the University of Washington in Seattle tackled a human problem by studying its equivalent in rats. He and his colleagues exposed a group of the animals to a 22-hour day, then checked gene activity within a clump of brain neurons called the suprachiasmatic nucleus, the site of the master clock. Some of the cells had realigned to the artificial 22-hour light-dark cycle while others were still keeping pace with the animals’ internal period of approximately 24 hours. In short, the cells followed separate biological clocks—one set by daylight, one not. Competition between the two could produce a confused internal time signal that is at the root of jet lag and some sleep disorders, says de la Iglesia: “If we can determine how the clocks are communicating, we might be able to figure out ways to improve it and treat these disorders.”