BEHAVIORAL EFFECTS OF CRANIAL IRRADIATION 679 



Motivation — Visual Exploration 



Subjects were 20 pied rats 90 days old. The experimental group contained 

 6 males and 5 females, and the control group contained 5 males and 4 

 females. The apparatus consisted of a plywood box, lOXlOXlOin. with a 

 a wire mesh floor and a translucent plastic top. In one wall, a 2 X 2 in. 

 window, located 1 in. above the floor, was covered by a door hinged so that 

 an easy push on the inside would cause it to fall and to open the window. 

 A guillotine door inside the box could be lowered to deny the rat access to 

 the window. 



Throughout the experiment, the rats lived in home cages plentifully sup- 

 plied with food and water. On each experimental trial, the latency of open- 

 ing the window was recorded. When it opened the window, the rat was 

 allowed to look out for 30 seconds. If the rat did not respond within 5 

 minutes, the trial was recorded as a failure. Ten trials per day were given on 

 the 7 days prior to irradiation. After irradiation with 5,000 r to the brain, 

 10 trials per day were given for the first 30 days. Testing then continued 

 every 5th day for the next 50 days. Next, massed satiation trials were given, 

 i.e., each rat was given continuous trials until it failed to respond on three 

 successive trials. Finally, long term tests were made 190-200 days after 

 irradiation. 



Results 



During the first 5 days after irradiation, the average latency of the experi- 

 mental group was virtually the same as that of the control group. Then, 

 beginning with the 6th postirradiation day, there was a sharp increase until, 

 by the 11th postirradiation day, the average latency for the experimental 

 group was 10 times that of the control group. Thereafter, there was a sharp 

 decrease in the latency of the irradiated group to a level about 2.5 times 

 greater than that of the control group, and this differential continued 

 through the remainder of the test trials. 



The results of the massed satiation trials are intriguing. Two of the male 

 rats (one irradiated and one control) were still responding after 5 hours of 

 testing — at which time the experimenter extinguished. During this time, the 

 control rat made 212 responses and the experimental rat made 192 responses. 

 All the other rats stopped responding. The difference in trials to satiation 

 for experimental and control groups was not significant. On the long term 

 tests, there was no significant difference between irradiated and control 

 animals. 



