Pulse modulated and continuous wave microwave radiation yield equivalent changes in operant behavior of rodents

Long-Evans rats were trained to the point of stable performance on a multicomponent (fixed-ratio, timeout) operant task. Different groups were exposed to continuous wave (CW) and to pulse modulated (PM) microwave radiation (MWR) during daily three-hour behavioral sessions. The rates of responding under actual and sham exposure conditions were noted. With comparable MWR dose rates, CW and PM MWR (5.8 and 6.7 mW/g, respectively) were equally effective in reducing response rates during both the fixed-ratio and the timeout components of the operant sessions. Dose rates of this order were associated with an elevation in body temperature of 0.5 to 1.0 degrees C. At 3.6 mW/g, whereas the mean rates of fixed-ratio responding were unchanged, the rates of responding during timeout were reduced significantly. Again, CW and PM MWR yielded essentially equivalent results. This MWR dose rate was not accompanied by a measurable increment in whole body temperature. It appears that (1) fixed-ratio operant responding of rats for food reward was more robust, that is, less subject to suppression by concurrent exposure to MWR than was bar-pressing during timeout, (2) PM and CW MWR, especially at the higher dose rate, effectively enhanced operant control over timeout responding and (3) the equivalent effects of CW and PM MWR support the hypothesis of a thermal basis for their effect despite the apparent inability to detect changes in whole body temperature.