656 SYLVAN J. KAPLAN 



Summary and Conclusions 



In two learning experiments, 114 normal control and prenatally irradiated 

 albino rats were divided into two age groups (90 and 400 days) at the 

 beginning of psychologic testing. 



All subjects were trained to a criterion of learning of 4 out of 5 consecutive 

 errorless trials on a Lashley III maze. Then 59 were randomly selected from 

 their respective radiation and control groups and trained on a bar pressing 

 instrument to measure experimental conditioning and extinction ability. 



The results indicated that while the data obtained from the maze study 

 yielded differences between groups receiving various doses of irradiation at 

 differing period^- in utero, data obtained from the conditioning study did not. 



No differences were found in the two groups of normal controls, but the 

 older irradiated animals exposed to 25-100 r were found to be significantly 

 inferior to normal control groups in maze learning ability. Learning deficit 

 was prominent in the 90-day-old groups only where conditions included 

 50 r at 7.5 days and 150 r at 8.5 days. A 90-day-old group given 200 r at 

 1.5 days was not adversely affected in learning in comparison to controls. 



The results lend credence to the hypothesis that magnitude of dose has a 

 functional relationship to relative radiosensitivity of tissue at all periods 

 throughout gestation, the function being revealed on the dimension of the 

 age at time of testing. 



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