LESIONS WITH ACCELERATED PARTICLES 337 



In the course of localized irradiation of the brain, special attention is 

 given to the possibility that if the body and nucleus of neuronal cells are in 

 the radiation field, the effect might be more profoimd than if only nerve 

 trunks are irradiated. Unfortunately, so far there seems to be no definite 

 evidence for such effect: in fact, demyelinization of fibers seems to occur 

 chronologically earlier than some othe effects. However, it is possible that fol- 

 lowing proper doses, fibers recover or even regrow from initial damage, while 

 it is anticipated that neurons might not recover from nuclear damage. 



Early radiation-induced changes include alteration of the blood-brain 

 barrier. If the lesion is massive, increased intracranial pressure might be one 

 of the early gross signs of damage. It is possible that electric disturbances, 

 resembling epilepsy, which sometimes follow massive head irradiation are 

 in part due to the increased intracranial pressure. Tilsjar-Lentulis and 

 Tobias ( 1959) in our laboratory observed cortical potentials following radia- 

 tion in rats and foimd that the epileptic fits were absent when the brain was 

 decompressed due to opening a large bone flap. In fact, using the cyclotron 

 radiation technicjue it was foimd that irradiation of one cerebral hemisphere 

 with doses in excess of 100,000 rads leads to immediate cessation of elec- 

 trical activity in that hemisphere. The other irradiated hemisphere still had 

 some acti\ity, but the alpha i hythm was about three times slower than 

 normal. Changes in excitability and transmission as a result of local irradia- 

 tion in various parts of the brain are the object of current studies. 



Stiiml'l.\tion by Means of Ionizing Particles 



The usefulness of nuclear beams in neurology would become even greater 

 if one were able to use radiation to stimulate nerve discharge, perhaps in 

 well-defined locations inside the brain. Several classes of observed psycho- 

 logic effects of radiation (e.g., see Miller et ai, this conference) indicate 

 that neuronal function is altered in some way following radiation, and we 

 do know that the retina can be directly stimulated with low doses of x-rays 

 (Lipetz, 1955). Hug (1960) has recently demonstrated interesting responses 

 in snails. Conard (1957) followed radiation effects in muscles of rabbit 

 intestine following radiation exposure. In preliminary studies at Berkeley, it 

 was realized that instantaneous stimulation of action cinrents in nerve might 

 recjuire high instantaneous radiation intensity for a brief period of time in 

 a similar fashion as high electric current densities are required for brief 

 periods of time to stimulate action currents. 



The Heavy Ion Linear Accelerator was chosen because it could deliver 

 pulses of one millisecond duration, up to 10" rad/min in intensity. For the 

 initial work a reflex was chosen which can be very easily demonstrated : the 

 corneal blinking reflex. As seen in Fig. 6, the cornea of unanesthetized rabbits 



