Real-time recording of neuropsychophysiological parameters during 50 Hz magnetic field exposure

In order to assess the possible effects of occupational levels of 50 Hz magnetic fields (MF) on human performance it is preferable to monitor performance during rather than subsequent to MF exposure. We previously reported studies of heart rate and cognitive behaviour where the issue of contamination was not a serious one. Our present study involves electrophysiological measures, which have a greater capacity to identify the effects and assist in localising them. The contamination of EEG signal by the MF exposure is clearly a problem in this type of study. Previous investigators have not reported these types of measurement concurrent with MF exposure due to the contamination difficulty; but this paper reports means of accomplishing this. Overall a combination of 12 methods for reducing pickup were employed. These were: 1) Distancing recording instruments from the MF source; 2) Shielding the devices and wiring; 3) Appropriate choice of cables; 4) Grounding the instrumentation; 5) Orientation of conduits; 6) Isolation of electrical mains power supplies; 7) Balancing the input impedances; 8) Applying a driven shield technique; 9) Improved electronics design incorporating pre-amplification and circuit impedance level control; 10) Analogue filtering; 11) Signal Averaging; and 12) Post acquisition digital filtering using frequency and time domain techniques.