MORPHOLOGIC AND PATHOPHYSIOLOGIC SIGNS 303 



co-workers (1959) and several other authors have described results obtained 

 by using ordinary EEG and corticogram traces or from investigations per- 

 formed with implanted electrodes. EEG's show that in rabbits and dogs 

 expMDsed to whole body irradiation in large doses (about 1,000 r), the bio- 

 electric activity and the irritability of the brain tissue are at first heightened 

 and subsequently lowered. Hypnotic phases are also observed in various parts 

 of the brain. 



Grigoryev (1958) found that variations in the EEG's of human subjects, 

 taken during therapeutic exposure to x-rays, could be detected 18 sec after 

 the beginning of the treatment. This effect occurred irrespective of whether 

 the head, abdomen, or whole body was exposed to the x-rays. After the first 

 exposures, however, the excitability of the nervous system was observed to 

 increase: subliminal (3-irradiation) stimuli gave distinct physiologic effects, 

 and the stimulation thresholds fell from between 6 and 12 sec to between 2 

 and 4 sec. 



Further irradiation led to a drop in the responsiveness of the cortex. The 

 number of paradoxical and ultraparadoxical responses to a strong light 

 stimulus increased. Stimulation by caffeine, instead of ordinary activation 

 of the electrical potentials, lowered the bioelectric activity; this indicates a 

 lowering of the working capacity of the nerve cells. Toward the end of 

 treatment, depression of the bioelectric activity usually set in, and the alpha 

 rhythm became faster and more widely diffused throughout the cortex. The 

 results of the first exposures were not stable and soon disappeared. Subse- 

 quent exposures produced radiation effects which lasted much longer. Com- 

 paring his findings with the dynamics of the excitation and inhibition 

 processes discovered by other methods, Grigoryev (1958) says that after ir- 

 radiation, the stimulatory process intensifies first, then diffuse inhibition 

 occurs. 



On the theoretical level, Grigoryev's observation that vegetative rhythms 

 appear in the cortex after irradiation, duplicating in frequency the cardiac 

 and respiratory rhythms, is of distinct interest. In his opinion and in that of 

 several other authors, the emergence of this rhythm indicates that the cerebral 

 cortex is being more intensively influenced by excited subcortical formations. 



Geinisman and Zhirmunskaya (1953) and Grigoryev (1958) stress the fact 

 that variations in the EEG are less pronounced after each consecutive x-ray 

 sitting and regard this as a manifestation of the central nervous system's 

 adaptation to repeated exposures by developing compensatory mechanisms. 

 Nevertheless, along with the adaptation phenomena there cannot fail to be 

 an accumulation of the variations occurring in the central nervous system 

 under the effect of ionizing radiation. 



Grigoryev (1956) and Tsypin (1956) found that when rabbits were 

 exfKDsed to whole body gamma radiation, even doses of 0.05-1.3 r caused 

 distinct changes in the electric activity of the brain. In many animals the 



