MUNsolved Mysteries

(Gazette, March 20, 1997)

Have a burning question pertaining to science, engineering, medicine, the arts, music, humanities, social sciences, physical education, or any other field? Let us know; we'll do our best to find the answers for you, drawing upon the expertise of members of the university community.

Remember the question we ran in MUNsolved Mysteries about how females in close proximity can end up with synchronized menstrual cycles?

Dr. Terry O'Grady, an assistant professor of obstetrics and gynecology in the Faculty of Medicine, explained at the time that the phenomenon involves pituitary hormones, and chemical substances which are secreted and released, called pheromones.

Dr. John de Bruyn, Department of Physics and Physical Oceanography {who holds the 1996 President's Award for Outstanding Research} said the phenomenon has also been used as an example of something called "mode locking."

"In the Gazette of Feb. 20, 1997, MUNsolved Mysteries contained a discussion of the synchronization of menstrual cycles among groups of women living in close proximity. Dr. O'Grady pointed out that this is viewed simply as a curiosity from the medical point of view. This phenomenon has in fact been cited as an interesting example of the general phenomenon of mode locking," Dr. de Bruyn said. "Mode locking can occur in a wide variety of physical, chemical, biological and other systems. The essential ingredients are two or more things which oscillate in time, and feedback or coupling between them. Depending on the periods of oscillation and the strength of the coupling, the oscillators can adjust themselves so that their periods become the same, or simply related, even though they may have been quite different originally."

Tick, tick, tick

Dr. de Bruyn used the example of synchronization occuring between two ticking clocks to explain how mode locking happens.

"Imagine two pendulum clocks hanging on a wall. The clocks initially tick at slightly different rates. When the first clock ticks, some of the energy produced by the tick is transmitted through the wall to the second clock. Similarly, when the second clock ticks, energy is transmitted to the first clock. This coupling between the clocks causes their [ticking pattern] to change slightly until they are 'in resonance,' that is, until they are the same, or in a simple ratio like 1/2, 1/3, 2/3...

Slime mold and satellites

"Mode locking occurs in mechanical systems, fluid flow, chemical reactions, electric circuits, charge transport in solids, cardiac cells, slime mold colonies, the brain, and satellite orbits: the moon always has the same side towards the earth because its period of rotation is in a 1/1 resonance with it orbital period.

"In the case of menstruating females, the oscillators are the hormonal cycles of the women, and the coupling results from the secretion of pheromones, as Dr. O'Grady explained. The remarkable thing is that despite the huge variety of systems which exhibit this behavior, a single, simplified mathematical model can describe them all."

There must be zillions of puzzling questions out there! Send yours to MUNsolved Mysteries, Gazette, Arts and Administration Building, Memorial University of Newfoundland, St. John's, Nfld., A1C 5S7; e-mail gazette@morgan., or fax 709-737-8699. Please include your name and telephone number.