Weak electric field interactions in the central nervous system.

Exposure to extremely low frequency electric and magnetic fields will induce electric fields and currents within the body, but these are almost always much lower than those that can stimulate peripheral nerve tissue. Guidance on exposure to such fields has been published by NRPB and ICNIRP, which is based on the avoidance of acute effects in the central nervous system. Weak electric field effects, below action potential thresholds, have been demonstrated in vitro in brain slice preparations; thresholds can be estimated to be above about 1 mV mm(-1) (around 100 mA m(-2), taking a brain tissue conductivity of around 0.1 S m(-1)), depending on stimulus conditions. Some studies suggest possible effects at lower induced field strengths. The intact nervous system might be expected to be more sensitive to induced electric fields and currents than in vitro preparations, due to a higher level of spontaneous activity and a greater number of interacting neurons. There is good evidence that electrically excitable cells in the retina can be affected in vivo by induced currents as low as 10 mA m(-2). It has been suggested that induced current densities above 10 mA m(-2) may have effects on other central nervous system functions but few studies have been carried out. Further research in experimental animals using both in vitro and in vivo approaches is needed to clarify this issue.