To examine the possibility of different pattern of brain heating by high-powered microwave exposure in rats. Temperatures were measured directly in the hypothalamus and cortex during heating by high-powered microwaves, warm water immersion (WWI), environmental heating (warm ambient environment, WSED), or exercise-induced heating (exercised on a treadmill in a warm ambient environment, WEX).
Exposure duration: 240 s
Exposure duration: 30 s
Experiment 1: rats were implated with rectal and brain temperature probes in the hypothalamus and cortex. Experiment 2: rats were implated with a single brain temperature probe , either in the hypothalamus or cortex.
The increase in hypothalamic temperature was significantly greater than those in cortical or rectal temperatures when animals were exposed to high-power density. Low-power density produced more homogenous heating. Quantitatively similar results were observed whether animals were implanted with probes in two brain sites or a single probe in one or the other of two sites. WWI produced uniform heating in the regions measured. Similar rates of temperature increase occured among regions following WSED or WEX, thus maintaining the pre-existing gradient between hypothalamic temperature and cortical temperature. The results indicate that high-power density produced a 2-2.5-fold difference in the rate-of-heating within brain regions that were separated by only a few millimeters. In contrast, more homogenous heating was found during low-power density or nonmicrowave modalities of heating.