The direct and delayed effects of exposure of subjects to a 50 Hz magnetic field on cognitive performance should be investigated.
The findings of Whittington et al. 1996, who found a significantly decreased reaction time in probands after exposure to a 50 Hz magnetic field, should be reproduced while being extended to investigate the delayed effects on recognition memory.
80 subjects participated in the study, 30 males and 50 females aged between 19 and 53 years, one half being exposed to the magnetic field (exposure group) and the other half being sham exposed (sham exposure group). Each group was subsequently equally divided into a morning and an afternoon session to account for potential time of day effects. A preliminary analysis revealed no time of day effects. Therefore, the data from morning and afternoon sessions were combined for the analysis of all test parameters.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
intermittent (1 s on, 1 s off) for 11 minutes
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | intermittent (1 s on, 1 s off) for 11 minutes |
| Exposure source | |
|---|---|
| Chamber | 4.5 x 5.5 m unshielded room, plastic chair with adjustable head rest |
| Setup | a set of Helmholtz coils (radius = 0.2 m) was suspended in each of four adjacent booths, such that each coil set was positioned at right angles to the sets on each side; the coils were wound onto a wooden form, each coil having 120 turns of 1.5 mm resin coated copper wire; the booths were constructed entirely from non-metallic materials; there was no detectable noise or vibration from the coils |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 100 µT | effective value | measured | - | - |
The recognition memory performance and decision confidence were significantly reduced in exposed subjects compared to sham exposed subjects.
No significant differences in reaction time and decision accuracy were found between exposed and sham exposed individuals in the visual duration discrimination assay. Hence, the results from Whittington et al. 1996 could not be confirmed.
Subjects and experimentators could not distinguish between exposure and sham exposure, thus ensuring the double-blind procedure.
As previous findings could not be reproduced but new possible effects were found, the authors conclude that it might be difficult to find reliable parameters for the investigation of effects of exposure to a 50 Hz magnetic field on the cognitive performance.
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