46 



ROBERT H. BROWNSON 



90 120 150 



TIME IN DAYS 



240 



Fig. 1. Behavior reaction pattern demonstrated by control and experimental animals 

 for food reward during 45 minute test periods. Slope of line to right indicates a gradual 

 extinguishment of learned reaction. Bar [jresses are plotted against time in days. 



bar piessins^ acti\ ity for food reward (Fis^. 1). Those animals which re- 

 cei\ed 1.000 r showed only minor deviation and after 228 days equaled the 

 control animals. The 2,000 r animal group showed a more striking initial 

 decrease but they. too. ecjualed the control animal performance by 228 days. 

 Animals receiving the accumulated doses of 3,000 and 4,000 r both demon- 

 strated a severe decrease in activity which reached the lowest performance 

 rates 7 days after receixing their last exposmes. Dinging the remaining sur- 

 vival period the 3,000 and 4,000 groups demonstrated little tendency to 

 increase from this low level acti\ ity. The obvious decline of all animal 

 performance o\ er the 5 weeks of testing, including controls, was attributed 

 to gradual extinguishment of learned behavior. 



Purkinje cells and granule cells of the cerebellum appeared to have imder- 

 gone certain similar changes at the various le\els of exposiue and time 

 intervals. These changes appear to have in\oIved a mild to se\ere loss of 

 Purkinje and granule cells. Hyperchromatic neiuons and pyknosis were 

 prevalent throughout most exposure levels. These alterations (Figs. 2 and 3) 

 were scattered throughout the cerebellum. 



Cerebral neurons demonstrated pyknosis and hyperchromatosis in scat- 

 tered areas throughout all le\els of radiation. Mild neurofibrillarv or axonal 



