Neuropsychological sequelae of 50 Hz magnetic fields

The effects of occupational levels of 50 Hz magnetic fields on cognitive function were studied on 30 human volunteers.

The exposure system consisted of Merrit-type modified Helmholtz coils forming a 2 m cube, employing two orthogonal sets of coils producing a 28 microT (resultant) circularly polarized 50 Hz magnetic field. Subjects sat at a desk within the coils where they undertook a series of verbal and written tests of cognitive function. After these tests were concluded (approximately 30 min) subjects were either exposed or sham-exposed to fields (double-blinded) for 50 min. A second set of tests (employing alternate versions) was administered 20 min from the start of this period. Each subject returned after 7 days to repeat the sequence, but with the opposite field/sham status.

The majority of the results indicated no significant effect of exposure on cognition. However, verbal recall of a list of 15 words after an interference (the different list) was significantly impaired in the 'field on' condition. This is indicative of a reduction in short-term memory of words. The mean baseline score was somewhat higher in the 'field on' condition. However, this difference is within the parameters of normal variation. The other significant result occurred during performance of a trail-making task (alternating 1-A-2-B-3-C, etc.), with a decrease in performance as a result of exposure to the 50 Hz field. This task requires executive functioning with a working memory load, involving parietal spatial processing coordinated by prefrontal executive processing. In summary, the data are suggestive of detrimental effects on cognitive processes, particularly short-term learning and executive functioning. However, larger sample sizes are required to demonstrate statistically a more specific pattern of cognitive effects.