The internal clock that controls the biological rhythms that in turn control so much of our lives — everything from determining whether we are morning or night people to what time we sag in the afternoon — does not tick the way scientists have long believed, according to mathematicians at the University of Michigan in Ann Arbor.

The location of the clock, in a region of the central brain called the suprachiasmatic nuclei has long been known. For decades scientists have believed the clock time is determined by the rate at which the cells fire their electrical pulses — fast during the day, slow at night.

The clock plays a role in cell division, heartbeat rates and a myriad other biological functions. Anyone who has experienced serious jet lag or a sleep disorder knows how bad your body can feel when your clock is out of sync with your surroundings. Understanding the clock is important in treating a host of diseases, including cancer. Doctors sometimes try to time a dose of chemotherapy medicine so that it enters the body when cancer cells are dividing at their fastest and normal cells are dividing at their slowest in a 24-hour cycle.

The new research, published in the current issue of the journal Science, developed a mathematical model showing that the suprachiasmatic nuclei cells don’t fire faster during the day and slower during the night, as had been assumed. Instead, the model predicted that the cells would only fire in brief bursts a couple of times in a 24-hour cycle.

The Michigan mathematicians, working with scientists from the University of Manchester in the U.K., then examined mice and found that the suprachiasmatic nuclei cells remained in an electrically excited state during the day, but did not fire. Then, around dusk, they would fire for a brief period, then go quiet again. At dawn, there would be another burst of activity, with signals being sent from the cells.

The findings “force us to completely reassess what we thought we knew about electrical activity in the brain’s circadian clock,” said Manchester’s Hugh Piggins. The work raises, but doesn’t answer, the question about whether the brain’s clock works in an analog or digital way, another researchers said.

This article was provided by Inside Science News Service, which is supported by the American Institute of Physics, a not-for-profit publisher of scientific journals.