In experiments on rabbits, we studied patterns of impulse trains generated by limited populations of neurons in the sensorimotor cortex (recording by a relatively thick microelectrode) prior to, in the course of, and after 1-min-long extrahigh-frequency (EHF) electromagnetic irradiation (wavelength 37.5 cm, power rate density 0.2 to 0.3 mW/cm 2 ). It was demonstrated that irradiation resulted in appreciable rearrangements of the bursting activity. Modifications affected (i) number of bursts, (ii) frequency of intraburst impulses, (iii) number of impulses in such bursts, (iv) burst duration, and (v) duration of bursts/duration of interburst intervals ratio. The pattern of these shifts depended, to a considerable extent, on the duration of the selected time window identifying the impulses as belonging to the burst. The effects described demonstrated rather complex dynamics; they were observed not only in the course of EHF irradiation sessions but also after their cessation.
INTRODUCTIONWhen studying the biological effects of nonionizing radiations, their influence on the functioning of the brain attracts special interest. In our earlier experiments where we analyzed electrical potentials in different cerebral structures and used a number of surgical operations, we demonstrated that direct action of electromagnetic fields (EMFs) of different frequencies, as well as that of magnetic fields (MFs), on cerebral tissues plays a leading role in the genesis of electrical reactions of cerebral structures [1][2][3]. It is obvious that the effects of electromagnetic extrahighfrequency (EHF) radiation should be studied, first of all, at the level of the cerebral cortex, since such radiation cannot significantly influence deeper cerebral structures [4,5].Information on the effects of decimeter-range EHF radiation on the functioning of central neurons of mammals remains rather limited [6][7][8][9][10][11][12][13]; in some aspects, our studies are pioneering. The history of the problem was described in our earlier publication [14]. We found that 1-min-long EHF irradiation of the head of an experimental animal resulted in significant changes in the evoked impulse activity of cortical neurons and did not noticeably change the frequency of the background activity [6,7]. In our further studies, we examined impulse trains generated by neuronal populations and not by separate neurons; such an approach made it possible to smooth the effects of random fluctuations, as well as to reveal the importance of leading rearrangements in neuronal activity. It was demonstrated [15] that the variability of neuronal activity can be neutralized in the functioning of the brain as a whole and also of separate cerebral structures at the expense of averaging neuronal ensembles. This approach allowed us to find that EHF irradiation induced mild changes in the frequency but more significant structural rearrangements of background impulse successions produced by populations of cortical neurons [8,[10][11][12][13]. In these studies, interest was concentrated...