Two previous studies (see publication 11906 and publication 10628) determined that exposure to pulsed extremely low frequency electromagnetic fields can affect the EEG, notably the alpha wave frequency (8-13 Hz). In the present study 22 participants from two previous studies (see publication 11906 [sequence 2 with a refractory period of 5000 ms] and publication 10628 [sequence 1 with a refractory period of 1200 ms]) and 10 additional subjects were randomly assigned to two different pulsed magnetic field sequences, used in the previous studies. Participation consisted of two sessions (exposure and sham exposure), separated by approximately 1 week (7+/-2 days).
|Exposure duration||continuous for 15 min|
|Pulse width||853 ms|
|Rise time||1 ms|
|magnetic flux density||200 µT||peak value||measured||-||-|
Compared to sham exposure, alpha wave activity was lowered over the occipital-parietal regions of the brain during exposure to sequence 1, while alpha wave activity over the same regions was higher after sequence 2 exposure. The effects occured after 5 min of exposure and were dependent on the order of exposure (magnetic field followed by sham exposure).
This study supports previous observations of EEG changes after 5 min pulsed extremely low frequency magnetic field exposure. The results also suggest that a previous exposure to the pulsed magnetic field sequence determined subjects´ responses in the present experiment, i.e. subjects previously exposed to sequence 1(and now to sequence 2) displayed higher occipital alpha wave activity after magnetic field exposure. Subjects previously exposed to sequence 2 (and now sequence 1) displayed lower alpha wave activity over posterior scalp regions in the present study.