occurred an interval of decreased total integrated EEG that persisted for up to 15 minutes. The authors
reported that the observed changes in the EEG resembled those induced by hallucinogenic drugs.
The nature of the EMF-induced EEG after-effect is determined by the exposure conditions and
the physiological characteristics of the subject (6-11). For example, following a 30 minute exposure at
100 µW/cm2, 3 GHz, most of the rabbits tested exhibit either depressed or elevated slow-wave activity,
and the relative number in each group varied with the location from which the EEG was recorded (6)
(Fig. 5.3). The activity in the hypothalamus and the cortex was highly correlated in individual animals-
it was either elevated or depressed simultaneously in both regions. After a 1 week exposure (1 hr./day)
depressed EEG activity was the characteristic response (6), and after 3-4 weeks the after-effect
phenomenon was no longer present (7). Dumanskiy observed a similar pattern in rabbits from exposure
to 1.9-10 µW/cm2, 50 MHz (8); after 2 weeks, EEG activity was elevated, but after 2. months'
exposure significant slowwave inhibition occurred. Such inhibition was also found after 4 months'
exposure at 1-10.5 µW/cm2, 2.5 GHz (9).
Fig. 5.3. Relation of EEG response from the cortex, hypothalamus, and brainstem due to exposure at 3
GHz. The numbers indicate rabbits with a given response.
Servantie showed that the EEG could be entrained by a pulsed EMF (10). For 1-2 minutes after
a 10-day irradiation period at 5000 ,µW/cm2 the EEG of rats exhibited the pulse-modulation frequency
of the applied 3-GHz field. Bawin (44) also observed the production of specific EEG rhythms, and the
reinforcement of spontaneous rhythms, by pulsed EMFs. Effects of EMFs have been reported on other
aspects of neuroelectric behavior, such as evoked potentials (12, 13, 73), neuronal firing rate (14, 15),
latency and voltage threshold (16),and response to drugs (73).
One of the American scientists who pioneered the study of EMF effects on the nervous system
is Allen Frey; his work has induded studies of the effects on evoked potentials (12.), behavior (17), and
hearing phenomena (18). In 1975 Frey reported an increase in the permeability of the bloodbrain
barrier (the selective process by which capillaries in the brain regulate transport of substances between
the blood and the surrounding neuropil) of rats exposed to 2400 µW/cm2 (continuous) or 200 µW/cm2
(pulsed) at 1.2 GHz (19). Frey found that dye injected into the bloodstream appeared in the brain of
exposed animals, but not the control animals, and that the pulsed EMF was more effective than the
continuous signal in opening the barrier, even though the average power level of the pulsed signal was
only one-tenth that of the continuous signal. Frey's findings were confirmed and extended by Oscar and
Hawkins in 1977 (20). They reported that continuous and pulsed EMFs both increased brain-tissue
ELECTROMAGNETISM & LIFE - 73