BEHAVIORAL EFFECTS OF CRANIAL IRRADIATION 671 



given 107 days after irradiation. On each test trial the rats were placed, one 

 at a time, in the center of the field, and the number of defecations and 

 urinations during a two minute interval was recorded. A dose of 2,000 r was 

 given in the first experiment; 2,500 r, in the second. 



Results 



In the first experiment, the irradiated male rats tended to be more emo- 

 tionally reactive than the controls, but no such tendency was found for the 

 females. The second experiment on males revealed a significant increase 

 in number of defecations after irradiation. The urination index did not yield 

 consistent results. These results indicate that in terms of the defecation index, 

 male rats show increased emotional reactivity during the first 30 days after 

 head irradiation. This was not true for females. 



Instrumental Learning 



The first experiment tested acquisition of an instrumental response after 

 2,000 r head irradiation administered 38 days prior to the beginning of the 

 experiment. In the second experiment, a dose of 2,500 r was given. In order 

 to have a battery of tests on the same animals, the same pied rats that had 

 been previously tested for emotionality were used in the first experiment. In 

 the second experiment, 40 Sprague-Dawley male albino rats were randomly 

 assigned to experimental and control groups of 20 rats each. 



In both experiments, a modified Skinner box with a horizontal bar extend- 

 ing through a hole in one side was used. When the rat pressed the bar, an 

 automatic feeding mechanism dispensed a small pellet of food into a food 

 pan below the bar. A shutter, which could be raised and lowered by the 

 experimenter, was located in front of the bar. 



The procedure was the same in both experiments except that, in the first 

 experiment, irradiation preceded acquisition, while in the second experiment, 

 irradiation occurred between acquisition and extinction. The dosage in the 

 first experiment was 2,000 r, and in the second it was 2,500 r. All animals 

 were run on a 22 hour hunger drive. In each trial, the animal was placed in 

 the box with the shutter lowered. The experimenter then raised the bar and 

 allowed the animal to make four bar-pressing responses, each of which was 

 reinforced by a pellet of food; the shutter was then lowered. The latency 

 of each response was automatically recorded by means of electrical time 

 markers and a Phipps-Bird polygraph. Training continued for 12 days (48 

 reinforced responses), and then extinction was begun. Each extinction trial 

 was the same as a training trial except that the feeding mechanism was 

 inoperative. The criterion of extinction was a period of 3 minutes in the box 



