Furthermore, the relation between response rate and power densitiy was investigated by using a complex schedule of reinforcement that generates both low- and high-response rates. Lever pressing was reinforced by food pellets on a fixed-interval schedule and produced for initial values without irradiation (baseline measurement) high rates of responding in two rats and low rates of responding in the other two rats.
Exposure at 37.5 mW/cm² disrupted the lever response in the two animals that responded at high rates during baseline measures. Exposure at the two lower power densities had no observable effect on the rate of responding. For the two animals that responded at low rates, no effects on rate of lever pressing were observed at any of the power densities. However, ambulatory activity of all animals decreased during exposure at 18.4 and 37.5 mW/cm². This decrease was associated with a tendency of the animals to remain in areas of the response chamber with lower power densities. The data are believed to be due to an interaction between higher metabolic rates in the more frequently responding rats and exogenous heating by microwaveirradiation.
