The effect of exposure to impulse X rays on normal and epileptic activity in rabbit brain.

Exposure to X rays (20 impulses of 4 Hz frequency, total dose 0.6-1.1 mGy) increased the epileptic activity of a focal area, which was produced in the visual cortex of rabbit brain by freezing with liquid nitrogen, and by stimulating with flashes of light at frequencies of 5-6 Hz. The number of seizure complexes during photostimulation for 5 s increased by 80% compared with the initial level, and this effect continued for 15 min. In control animals (with no epileptic foci), a decrease was observed in the main frequencies of the delta rhythm and the theta rhythm (by 90% and by 10%, respectively) over the cortex as a whole. In rabbits with experimental epilepsy, the delta rhythm decreased only in the frontal lobes and in the lateral geniculate body (by 30%), whereas the theta rhythm decreased only in the visual cortex (by 10%). Possible mechanisms for these effects are discussed.