BEHAVIORAL EFFECTS OF CRANIAL IRRADIATION 673 



irradiation. All irradiated groups learned the maze in fewer trials, had faster 

 running times, and were less variable in performance than control groups. 

 In trials to learn, the differences between experimental and control groups 

 became smaller as a function of delay in beginning training. Although 

 histologic examination revealed that brain tissue in some of the irradiated 

 rats had been damaged, it was suggested that a combination of increased 

 hunger motivation and reduced exploratory drive produced the differences 

 in performance. 



The last experiment was designed to test ( 1 ) whether increased hunger 

 following radiation sickness adequately accounted for facilitation of maze 

 performance, (2) whether possible detrimental effects of brain irradiation 

 might be masked by increased hunger motivation following radiation sickness, 

 and (3) whether radiation sickness and/or facilitation of maze performance 

 might be produced by irradiating a body area other than the head with a 

 dose equivalent to that applied to the brain area. This experiment compared 

 the performance in a 14-unit multiple T-maze of 110 rats divided into the 

 following four matched weight groups: a brain-irradiated group, a group 

 that received an equivalent dose of irradiation to the right hind leg, a group 

 starved so as to lose the same amount of weight lost by the brain-irradiated 

 group, and a control group. The animals were weighed each day and those 

 in the starv-ation group were given the appropriate amount of food to main- 

 tain their weight at the same level as that of the brain-irradiated group. 



Results 



As in previous experiments, the brain-irradiated animals lost weight 

 rapidly and reached a minimum 12-15 days after irradiation. Weight loss 

 of the starved animals matched that of the brain-irradiated animals; how- 

 ever, the leg-irradiated animals did not lose weight. In each experiment, the 

 average weight of the leg-irradiated group closely matched that of the 

 control group. These findings, along with daily observations of behavior, 

 clearly indicated that the radiation sickness syndrome obsened in the brain- 

 irradiated animals was not produced by an equivalent dose of irradiation 

 applied to another part of the body, specifically, to the hind leg. 



Both stai-vation and brain-irradiated animals perfonned better than the 

 controls. The starvation animals performed better than the brain-irradiated, 

 but the difference fell short of statistical significance. The performance of 

 the leg-irradiated animals was erratic. In the first experiment, it approxi- 

 mated that of the starvation animals and was significantly better than that 

 of the controls while, in the third experiment, it approximated that of the 

 controls. 



Considering these results in the light of our previous maze learning test 



