Adapting to heat and cold.

Setting the thermostat in a household or business so that everyone is comfortable usually is impossible. Husbands and wives fight over the setting on the electric blanket. The very young and very old suffer during the temperature extremes of both summer and winter. People going back and forth between outdoor heat and air-conditioned buildings report feeling sick and dizzy. All these examples illustrate demands made on a person's internal "thermostat"--a highly individual and complex system of blood vessels, nerves, and brain tissue that still is not well-understood, indicates Robert Foreman, chairman, Department of Physiology and Biophysics, University of Oklahoma Health Sciences Center. Although all human beings operate at an average ideal temperature of 98.6[degrees] Fahrenheit, each person has his or her unique tolerance level for heat and cold. "We all have the ability to make quick temperature adaptations. For example, when you step in the shower it immediately feels either too hot or too cold. For a moment, it's very uncomfortable, but that quickly changes. The receptors in the skin adapt very quickly to that stimulus."

The skin plays a key role in the body's reaction to temperature change. Heat and cold receptors convey information to the spinal cord, which passes it to the anterior hypothalamus in the brain. "That's where we think the so-called `thermostat' control is located," Foreman notes. "The fact that we call it a thermostat demonstrates how naive we still are about how it regulates temperature. From the central nervous system point of view, we simply don't know very much at all." What is...