484 WALTER R. STAHL 



histologic brain atrophy. No Soviet papers demonstrate such changes 

 following small antenatal doses. 



The fact that a CR stereotype could be produced at all under these 

 conditions raises the question of the sensitivity of the CR method. Pavlov 

 noted that the conditional reflex is a basic type of reaction which can occur 

 in primitive animals and after extirpation of substantial portions of the 

 cortex. After radiation the question is clearly not one of complete failure 

 of CR production, but rather of subtle disturbances in higher nervous 

 activity which are nearly, but not quite fully, compensated by feedback 

 mechanisms. 



Antenatal irradiation is of particular interest in that it makes possible the 

 production of nonspecific functional brain damage. The work on CRs sug- 

 gests that inhibitory control is damaged particularly, and one might speculate 

 that psychopathic personalities also lack normal inhibitory control. Further 

 experimentation on emotional or motivational control following antenatal 

 irradiation appears promising. 



Conclusion 



It does not seem possible to provide a simple, satisfying summary of the 

 multitude of complex experiments discussed. Clearly any definitive statement 

 about CNS sensitivity must go into considerable detail concerning the mech- 

 anism involved and the form of sensitivity under consideration. 



A final conclusion concerning CNS radiosensitivity must also take cogni- 

 zance of certain clinical observations on radiation exposures, namely : pjersons 

 receiving even high doses feel no pain and only equivocal mild sensations; 

 humans getting doses of 500-1,000 r do not ordinarily show any obvious 

 neurologic disturbances, and treatments directed at the nervous system have 

 not been helpful in combatting radiation sickness. Many ordinary virus 

 infections appear to produce more obvious encephalopathy than radiation, 

 and numerous chemicals now used in the environment might evoke CNS 

 reactions as great or greater than those seen after radiation exposures at 

 moderate levels. 



Not all Soviet radiobiologists place special stress on CNS mechanisms in 

 radiation sickness. They point out, however, that the nervous system is a 

 major organ system and ought to be given attention in radiation studies, 

 during the last two years, there has been a relative decrease in the Soviet 

 literature of papers stressing CNS effects, particularly those works citing the 

 formal Pavlovian view on the pathophysiology of radiation sickness. 



Following exploration for damage from radiation, certain interesting 

 questions of basic biology have now become apparent in connection with 

 CNS radiation exposures: 



