304 N. I. GRASHCHENKOV 



cortical responses were at first enhanced when tested by photic stimulation, 

 but when the dose was increased to 7.8 r, cortical responsiveness and excita- 

 bility diminished to the point at which there was no response at all to light 

 stimulus. 



It follows from the research described above that even small doses of 

 radiation energy (0.05 to 2, 5, or 10 r) are sufficient to cause detectable trace 

 functional changes in the nervous system. The accumulation eflFect indicates 

 that physiologic changes are at the root of this phenomenon. It can be as- 

 sumed that even the natural level of radiation leads to similar changes, 

 although this will overlap with repair processes in the nerve tissues. 



The changes in the nervous activity described, occur under the eflFect of 

 whole body radiation and under local irradiation of the head (Meshchersky, 

 1958; Fanardzhyan et al., 1960). 



The dynamics of the EEC's display certain characteristic features which 

 make it possible to diflferentiate the reflex from the local responses of the 

 brain to irradiation. 



Grigoryev (1958) notes that a lowering of the electrical potentials is ob- 

 served following irradiation of the head. In whole body irradiation, the 

 EEG response depends on the initial background, and the variations in the 

 EEG are more generalized and as a rule localized in the opposite hemi- 

 sphere to the one which is irradiated. 



With local irradiation of the temporal regions, variation in the electrical 

 activity is observed within the irradiated zones of the brain or, at any rate, 

 predominantly in these. We can therefore assume that the variations ob- 

 served in the EEG's are both local and reflex in etiology. 



The considerable shifts observed in the interrelationship of the vegetative 

 and endocrine systems as a result of radiation lesions are naturally leading 

 investigators to pay attention to the influence of ionizing radiation on the 

 functions of the hypothalamic and diencephalic parts of the brain and on the 

 activities of the dififerent links in the vegetative nervous system. 



Work done in the laboratory of Livanov and Efremova (1957) has shown 

 that 1 to 3 days after single whole body exposure (1,000 r), there is an 

 abrupt change in the bioelectric activity of a rabbit hypothalamus. The 

 variations in potential become more intensive, and there are recurrent spas- 

 modic discharges in sharp waves. The response of the cerebral cortex to 

 hypothalamic stimulation undergoes sharp variations and at times is even 

 distorted. There is a lowering of the thresholds of the stimulations required 

 to elicit the characteristic behavior responses (sniflfing, licking the lips). The 

 rise in bioelectric activity is subsequently replaced by a lowering. 



Phase disturbance of the hypothalamic activity after mass irradiation of 

 experimental animals has also been noted by Smirnova (1958) and Kon- 

 drateva (1957). 



There is an increasing amount of evidence that other links in the vegeta- 



