Effects on the nervous system by exposure to electromagnetic fields: experimental and clinical studies

Exposure to electromagnetic fields may cause various types of effects on nervous tissue, in severe cases even irreversible damage. The exposure conditions, i.e. frequency including type and extent of modulation, time, intensity, wave form, as well as shape, size and position of exposed subject and possible treatment with drugs, are factors determining if damage, acute or chronic, ultimately result. Long term exposure of newborn rabbits, rats and mice to electromagnetic fields of power frequency (10-14 kV/m; 50 or 60 Hz; sinusoidal wave form; 21-24 h per day) may cause affection and even damage to the nervous system. Large nerve cells showed reactive changes such as lamellar bodies and cytoskeletal alteration to an extent varying with exposure conditions. Reactive neuroglial changes as well as increase in neuroglial marker proteins could concomitantly be demonstrated. The changes seemed to be reversible although we only have incomplete data available. Exposure in vitro of frog sciatic nerve to 16-60 Hz sinusoidal low current (50-1000 nA) for 17 h induced cytoskeletal changes. Exposure of rabbits to pulsed microwaves of moderate to high intensity (3.1 GHz; 300 Hz modulation; peak duration 1.4 usec with maximal peak intensity about 1000 times average; 55 mW/cm; SAR in the brain cortex about 20 W/kg; increase of temperature as measured by lightguide-equipped instruments in right brain hemisphere about 1-2 degrees C) during 1 h per day during three days resulted in no obvious initial changes in behaviour. Minimal acute dam- age could be demonstrated. However, after two to four months and later on both structural, immunohistochemical and biochemical changes could be documented. Radar technicians accidently and/or occupationally exposed to microwaves showed psychoneurological signs of affection as well as changes in cerebrospinal fluid protein pattern. No related changes have been noticed among matched controls. Exposure of nervous tissue to electromagnetic fields ranging from power frequency to microwaves may thus exert a wide range of effects, mostly by mechanisms we know little about.