PERFORMANCE AFTER IRRADIATION TO THE HEAD 707 



were determined by halving the head of one monkey midsaggitally. The 

 areas of radiation were identified, and holes that marked the corners of the 

 patterns were bored from the interior surface of the skull, through the skull 

 and through the skin. The external boundaries were drawn by connecting 

 the points made by the drilled holes. Each subject was prepared for irradia- 

 tion individually, and slight compensations were made for structural varia- 

 tions of individual skulls. 



The radiation source was a self-rectifying half-wa\e 260 kvp, 18 ma 

 Picker therapeutic x-ray machine with an inherent filtration of 0.25 mm Cu 

 plus 2 mm Al. The following radiation factors were employed : 1 mm Al and 

 0.25 mm Cu filtration added, voltage of 250 kvp, and current of 18 ma. Prior 

 to irradiation, each monkey was intravenously given 14 mg of sodium pheno- 

 barbital per kg of body weight, and almost instantaneously went into surgical 

 anesthesia. The monkey was placed on its back at right angles to and 100 cm 

 from the x-ray beam. Its body was shielded by two 0.25 in. lead sheets placed 

 at target-to-object distances of 80 to 87 cm. The x-ray beam was collimated 

 by directing it through rectangular holes in the lead sheets. The size of the 

 collimated beam at the exposure distance (100 cm) was checked several 

 times with film and was found to correspond to the size of the desired 

 pattern. The head was propped so that the beam completely covered the 

 area of the desired drawn pattern. The boundaries of the pattern were 

 further limited by 0.25 in. thick caps fashioned from lead sheeting, cut to the 

 particular pattern, and fitted over the head. The dose rate measured with 

 an NBS calibrated 25 r Victoreen Chamber was 20.5 r per min. The dose 

 rate measured with an Air Force water-equivalent chemical dosimeter was 

 21.8 r per min. The dose rate measured by the Air Force chemical dosimeters 

 was chosen, since this dosimeter was standard for the Radiobiological 

 Laboratory. 



Two periods of irradiation were preceded and separated by training. 

 During 6 months of preliminary training, the animals became proficient in 

 doing eight selected laboratory tasks, six given in the Wisconsin General Test 

 Apparatus, (VVGTA) (Harlow and Settlage, 1948), requiring the selection 

 of objects. 



After 12 days of massed practice on all eight tasks, each subject was anes- 

 thetized and restrained in the radiation chamber. The experimental animals 

 were irradiated with 3,000 r x-radiation. Controls were sham irradiated. On 

 the day following treatment, all were returned to the laboratory and trained 

 during each of the following 27 days. Those in the experimental groups were 

 irradiated with a second similar 3,000 r dose 28 to 30 days after the first 

 irradiation. Following the second irradiation, they were trained during 27 

 days spaced over 38 calendar days. 



