The effects of a weak, extremely low frequency pulsed magnetic field upon human brain electrical activity.

摘要

Electroencephalography (EEG) is a method of indirectly measuring human brain electrical activity from the scalp. It is a fast and informative way to examine brain responses to various sensory stimuli. In this thesis, I have investigated how a weak (+/- 200 muTesla) pulsed, extremely low frequency (< 300 Hz) magnetic field (ELF MF) affects human brain electrical activity. Normal subjects were assigned to receive both a 15 minute pulsed MF and a sham, randomized for order. Possible differences in the EEG induced by the pulsed MF were compared to the sham exposure.;In Experiment 2, the EEG was assessed during the pulsed MF exposure period. I found that occipital alpha activity was again affected, significantly lower after 5 min of pulsed magnetic field compared to sham. The pulsed MF sequence was slightly modified for this experiment, which seemingly induced problems in replication of some of the results found in experiment 1.;In Experiment 3, an attempt was made to replicate the results found in experiments 1 and 2 by using the two different pulsed MF sequences used previously. Subjects who participated in Experiments 1 and 2 were recruited and assigned to receive the other sequence to which they had not been exposed. I found that occipital alpha activity was yet again significantly affected by the pulsed MF after 5 min of exposure. The direction of the effect was different for the two pulsed MF sequences. I found that the subject's EEG response to the newer sequence was determined by their first exposure.;This thesis has demonstrated that pulsed MFs, known to affect aspects of animal and human behaviour, can affect human brain electrical activity after 5 min of exposure.;In Experiment 1, I found that the pulsed MF affects the EEG in a manner consistent with the results of other published studies. Alpha activity (8-13 Hz) measured over the occipital region was found to be higher in the 1 st minute post-MF exposure compared to sham exposure. This effect was also found to persist for several minutes into the post-exposure period, highlighting a need to assess for possible 'wash-out' effects of the MF.