ACTION OF GAMMA RADIATION ON ELECTRICAL BRAIN ACTIVITY 613 



Weak irradiation with 400 r produces a marked acti\ation of the archi- 

 cortex (hippocampus) after only 30 minutes with faster rhythms, spike 

 potentials, and some sharp waves. These symptoms increase steadily, espe- 

 cially the spike potentials, during the experiment, 3—4 hours after 

 irradiation. Simultaneously, the neocortex shows early alterations. The 

 high voltage slow activities (3 cps) of the previous resting state are replaced 

 by low voltage faster activities with numerous sharp waves in the whole 

 neocortex and even in the subcortex (thalamus). These symptoms suggest 

 some early excitatory action of the gamma radiations (Fig. 4). 



Stronger irradiation with 600 r confirms the early hyperactivity of the 

 hippocampus with spike potentials of high amplitude and frequency. In 

 the neocortex and subcortex, there is a progressive tendency towards de- 

 synchronization. The previous "high voltage slow waves and spindles" activ- 

 ities are replaced more and more by low \oltage fast rhythms with sporadic 

 sharp waves ( Fig. 5 ) . 



Strong irradiation with 900 r shows a different electrographic picture: 

 after 30 minutes a '"high voltage slow wa\e syndrome*" de\elops with numer- 

 ous spindles. Fi\e per sec rhythms and sharp waves are also present in the 

 neocortex and thalamus. In the archicortex, there is strong hippocampal 

 hyperactix ity with series of spike potentials, sharp wa\es. and high voltage 

 slow wa\es. All these symptoms reach a maximum after 3 and 4 hours 

 (Fig. 6). 



From these obser\ations. we mav conclude that weak gamma irradiations 

 (400 and 600 r) tend to desynchronize the spontaneous electrical activity of 

 the neocortex. Low \oltage fast rhythms and sharp waves of irritative char- 

 acter replace the prc\ious high \oltage slow waxes and spindles syndrome 

 of the resting brain. In the archicortex. the hippocampus shows a marked 

 hyperactivity, with series of high and frequent spike potentials and sharp 

 waves. These alterations begin 30 minutes after irradiation and reach a 

 maximum after 3-4 hours, concomitant with a hyperactive motor behaxior 

 involving increased oral patterns. Strong gamma irradiation ( 900 r ) tends, 

 on the contrary, to synchronize the whole brain activity at a low frequency 

 (1-3 cps). Irritative symptoms, such as faster rhythms (5 cps), sharp waves 

 in the neocortex, and precritical hyperactivity in the hippocampus, persist. 

 These alterations reach a maximum alter 3-4 hours; simultaneously, an 

 abnormal passivity of beha\ior occms. 



