MORPHOLOGIC AND PATHOPHYSIOLOGIC SIGNS 301 



Pathologic Signs of the Action of Ionizing Radiation 



One cannot discuss the effect of ionizing radiation on the functioning of 

 the nervous system without mentioning the early research on this subject 

 in the Pavlov-Nemenov laboratories in the late 1920's. This was the period 

 when the view that the nervous system is highly radioresistant was widely 

 propagated in the literature — an opinion held to this day by a great many 

 foreign authors, but based on the morphologic research of that time. 



Nemenov (1932, 1950), however, by using the conditioned reflex method 

 was able to demonstrate that this view was incorrect and to provide con- 

 firmation that the nervous system is radiosensitive. Today we have accumu- 

 lated extensive information on disturbances of the higher nervous activity by 

 exposing various experimental animals and human subjects to radiation and 

 studying its effect on their conditioned reflex activity. As this material has 

 been dealt with in a number of reviews and monographs, I shall confine 

 myself to outlining the results obtained from work done in the last few years. 



These researches have shown that various types of ionizing radiation lead 

 to phase changes in the neurodynamics of the cortex. During the initial 

 periods the cortical activity is stimulated, but later, depression sets in. The 

 duration of each period depends both on the condition of the nervous system 

 and on the dose and characteristics of the radiation. 



In recent years the work of Kotlyarevsky and co-workers (1957), Livshits 

 (1955, 1956a, b), Lomonos (1953), and Piontkovsky and co-workers (1957) 

 has provided confirmation that phase changes occur in the higher nervous 

 activity after whole body exposure of experimental animals to small or 

 medium doses of radiation. Lomonos (1959) noted phase changes in the 

 conditioned reflex activity after the body of a dog had been exposed first to 

 a single and then to repeated doses of radiation with its head shielded. In 

 several cases, prolonged disturbances of the conditioned reflex activity have 

 been observed without any clinical signs of radiation sickness. 



Klimova (1957) observed persistent changes in the higher nervous activity 

 without clinical symptoms of radiation sickness following internal irradiation 

 of animals (dogs) fed 1 ^c each of radioactive strontium for 6 months. She 

 found that the conditioned reflex activity was at first heightened, then 

 depressed, and that phase conditions appeared in the cerebral cortex. Four 

 to 6 months after irradiation, similar disturbances were observed in the 

 unconditioned reflexes. Restoration of the nervous activity took place un- 

 evenly. The motor defense reflex was the first to return to normal at the end 

 of the 1st month, followed by the motor food reflex, and 2-2/2 months later 

 by conditioned reflex activity. Various defects were still observed in the 

 dogs' higher nervous activity even 6 months after the exj>eriment. 



With large doses of ionizing radiation, the initial phase of cortical activa- 



