REVIEW OF RESEARCH IN U.S.S.R. 477 



and dogs and is typified by the work of Livshits (1956), Yarullin (1959), 

 and Lomonos (1957, 1959). These experiments may show a slight stimula- 

 tory efTect initially, but more commonly they show depression of the CRs 

 a few weeks after exposure. The possibility of an indirect somatic effect, 

 such as suppression of salivatory activity, must enter into the interpretation 

 of these findings. Most studies suggest depression of CRs after several 

 hundred r, at some time after exposure. 



However, quite a few Soviet authors, such as Korol'kova (1958) and 

 Biryukov (1957), noted slight or insignificant alterations in certain CR 

 experiments after 1,300-5,000 r (chronic exposure, usually). It is doubtful 

 that these authors would deny any effect on a CR with low doses, but in 

 some studies they were able to produce quite normal new CRs even after 

 thousands of r. 



Thus, it is apparent that there is no unanimity at present as to whether 

 the CR method shows very low level radiation alterations or whether it is 

 a highly sensitive indicator of damage. More work will have to be done on 

 this matter, and it will have to be fully controlled statistically; the interpre- 

 tation must differentiate between direct effects on the CNS and indirect 

 actions through somatic organs. 



Other types of tests of general higher nerve functioning after radiation 

 include studies on experimental neuroses following exposure. Korol'kova 

 (1958), workers at the Sukhumi primate laboratory in the U.S.S.R. (per- 

 sonal communication), and others indicate that experimental neuroses 

 develop quicker, are more severe, and last longer after irradiation. In a 

 general way, some researchers indicate a "weakening" of higher nervous 

 activity, particularly in regard to inhibitory control. Livanov (1957, 1959; 

 Livanov et al., 1960a, b) has stressed repeatedly that such injury may be 

 hard to detect because the CNS compensates for the insult almost immedi- 

 ately; he feels CNS radiation damage is nonthreshold and cumulative. 



Substantial portions of the cortex have been removed in experimental 

 animals without drastic, sometimes without any discernible, effects on CR 

 and behavioral tests. These techniques would hardly be expected to reveal 

 damage to a small percentage of neurons in the cortex or elsewhere. One 

 can probably speculate that negative feedback, compensatory mechanisms 

 are present in all parts of the CNS, as are nonlocalized pattern transfer 

 systems. As pointed out by von Neumann, one can make reliable devices out 

 of unreliable components by multiplexing circuits, and, therefore, it seems 

 that slight damage in the CNS will be exceedingly hard to demonstrate by 

 ordinary methods. 



Special test methods may turn out to be of the greatest interest from this 

 viewpoint. For example, one may mention the report on audiogenic seizures 

 in mice, presented at this conference, and work by Biryukov (1957) showing 



