The temperature hovers around freezing, but the sun is up for 24 hours each day. How do animals living in the continuous light of the Arctic summer know when to sleep and when to be active? Do they maintain a 24-hour cycle of rest and activity, or does living in continuous light alter their circadian rhythm?
Answering these questions may improve our understanding of biological clocks -- the internal, genetically programmed cycle of rest and activity that affects the behavior, metabolism and physiology of all animals, including humans. A better understanding may also help solve problems -- such as shift-work fatigue, jet lag and even seasonal affective disorder -- that are associated with disruptions of biological clocks.
One scientist who has spent a lifetime pursuing these questions and finding answers that have helped build the field of biological clock research is G. Edgar Folk, Ph.D., emeritus professor of molecular physiology and biophysics at the University of Iowa Roy J. and Lucille A. Carver College of Medicine.
Folk notes that humans have a natural circadian rhythm of close to, but not exactly, 24 hours. Importantly, all biological clocks are adjustable and respond to environmental cues such as sunrise or sunset, which continuously reset the clock and keep us on a regular 24-hour schedule.
However, previous research, including studies in Folk's lab, has shown that lab rats kept in continuous light develop a 26-hour cycle of rest and activity, meaning their peak of activity travels around our usual daily 24-hour clock. This phenomenon is called the Aschoff Effect after a German scientist who first recorded it in the 1960s. Folk sometime ago set out to determine if this effect was also seen in wild animals during the continuous light of the Arctic summer.
"In continuous light in the lab, the animal's clock changes depending on the intensity of the light," Folk explained. "We thought that would also happen i
Contact: Jennifer Brown
University of Iowa