Behavioral thermoregulation in the squirrel monkey: adaptation processes during prolonged microwave exposure.

During 10-min exposures to 2450-MHz microwaves at a power density of 6-8 m W/cm2, squirrel monkeys reliably select a cooler environment. Exposure duration, at power densities above and below this threshold, was the parameter investigated in these experiments. Monkeys were restrained in the far field of a horn antenna inside a 1.8 x 1.8 x 2.5 m anechoic chamber which was heated and cooled by forced convection. The animals learned to control the temperature of the circulating chamber air by selecting between cold (10-15 degrees C) and warm (50-55 degrees C) air sources. During the experiments, they were exposed to 12.4-cm (2450-MHz) continuous-wave microwaves for periods from 5 to 150 min. Microwave power densities explored were 4, 10, and 20 mW/cm2 which represent rates of whole-body energy absorption that range from approximately, .6 to 3.0 W/kg. No microwaves were present during 4-hr control experiments. The 4 mW/cm2 microwave exposure did not modify thermoregulatory behavior, no matter how long it lasted. The 10 and 20 mW/cm2 exposures stimulated the monkeys to select ambient temperatures 1.5 and 3.0 degrees C cooler than control levels, respectively. Except during the first microwave presentation of a series, or during the early minutes of a single long exposure, duration had no significant effect on selection of air temperature or on the body temperatures achieved thereby.