Microwaves modify thermoregulatory behavior in squirrel monkey

Abstract

Squirrel monkeys (Saimiri sciureus) trained to regulate environmental temperature (T_a) behaviorally were exposed in the far field of a horn antenna to ten-minute periods of 2,450 MH_z CW microwaves. Incident power density ranged from 1 to 22 mW/cm². The corresponding specific absorption rate (SAR), derived from temperature increments in saline-filled styrofoam models, ranged from 0.15 to 3.25 W/kg. Controls included exposure to infrared radiation of equivalent incident energy and no radiation exposure. Normal thermoregulatory behavior produces tight control over environmental and body temperatures; most monkeys select a T_a of 34–36°C. Ten-minute exposures to 2,450 MH_z CW microwaves at an incident power density of 6–8 mW/cm² stimulated all animals to select a lower T_a. This threshold energy represents a whole-body SAR of 1.1 W/kg, about 20% of the resting metabolic rate of the monkey. Thermoregulatory behavior was highly efficient, and skin and rectal temperatures remained stable, even at 22 mW/cm² where the preferred T_a was lowered by as much as 4°C. No comparable reduction in selected T_a below control levels occurred during exposure to infrared radiation of equal incident power density.