Operant control of convective cooling and microwave irradiation by the squirrel monkey

Adult male squirrel monkeys ( Saimiri sciureus ) were individually chair‐restrained in an air‐conditioned Styrofoam box in the far field of a horn antenna. Each monkey first received extensive training to regulate the temperature of the air circulating through the box by selecting between 10 and 50°C air source temperatures. Then, to investigate the ability of the animals to utilize microwaves as a source of thermalizing energy, 2450‐MHz continuous wave microwaves accompanied by thermoneutral (30°C) air were substituted for the 50°C air. Irradiation at each of three power densities was made available, ie, at 20, 25, and 30 mW/cm 2 [SAR = 0.15 (W/kg)/(mW/cm 2 )]. The percentage of time that the monkeys selected microwave irradiation paired with thermoneutral air averaged 90% at 20 and at 25 mW/cm 2 . The mean percentage declined reliably (p < 0.001) to 81% at 30 mW/cm 2 , confirming the monkey's ability to utilize microwave irradiation as a source of thermal energy during the course of behavioral thermoregulation. All animals readily made the warm‐air to microwave‐field transition, regulating rectal temperature with precision by sequentially selecting 10°C air, then microwave irradiation accompanied by 30°C air. Although the selection of cooler air resulted in a slight reduction of skin temperatures, normal rectal temperature was maintained. The results indicate that the squirrel monkey can utilize a microwave source in conjunction with convective cooling to regulate body temperature behaviorally.