EFFECTS OF PRENATAL RADIATION UPON LEARNING 647 



tical lesions and normal controls, investigators studying maze learning have 

 selected this instrument for examining irradiation effects on learning. Their 

 success in establishing differences in Lashley III maze performance in the 

 prenatally irradiated rat, exposed to 90-600 r, has been reported (Furchtgott 

 et al., 1958; Levinson, 1952; Tait et al., 1952). All these studies, however, 

 have utilized young animals in the learning experiments and have devoted 

 their attention to subjects irradiated on or beyond the 11th gestation day. 

 Therefore, no information exists to establish the nature of the learning 

 behavior resulting from these and smaller dose levels given prior to gestation 

 day 11. 



Since Hicks (1953), Rugh (1959a, b), and Rugh and Grupp ( 1959a, b) 

 have called attention to the radiosensitivity of embryonic tissue prior to this 

 day in rat and mouse gestation, it was considered important to investigate 

 these factors as they might be revealed in aberrant learning behavior. 



Apparatus and Procedure 



Subjects were given preliminary training in a six-ft-alley runway to estab- 

 lish a goal-directed running tendency. Each rat was placed on a 23/2 hour 

 food deprivation schedule 2 days prior to commencement of this training. 

 During this period they were handled so that they would become accus- 

 tomed to the experimenter. Subjects then were given two runs daily for 

 5 days, being allowed 30 sec at the end of each run to eat a wet mash food 

 placed at the end of the runway. Then they were returned to their cages 

 and given three Nutrena nuggets. This diet preserved the subjects' weights 

 and maintained a level of hunger drive to insure adequate motivation 

 throughout the experiment. 



One day after completion of preliminaiy training, all subjects were given 

 one trial daily in the Lashley III Maze (Fig. 1). They were scored for time 

 (opening of the starting box door to entry into the goal box) and for full 

 or partial forward going errors and retrace errors. 



Results 



Each group was tested for a significant difference from every other group 

 by a f-test for mean number of trials required to reach the trial which 

 preceded the criterion of mastery (4 out of 5 consecutive errorless trials). 

 The Mann-Whitney U test (Siegal, 1956) was used to test significance 

 between groups for mean number of errors and mean time for trials until 

 the criterion of mastery was achieved. Computations for trials and errors 

 to achievement of criterion excluded the scores for criterion trials, but in- 

 cluded mean time scores. 



