Neuropsychological sequelae of 50 Hz magnetic fields

Purpose : The effects of occupational levels of 50 Hz magnetic fields on co gnitive function were studied on 30 human volunteers. Materials and methods : The exposure system consisted of Merrit-type modifi ed Helmholtz coils forming a 2 m cube, employing two orthogonal sets of coi ls producing a 28 muT (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 conc luded (similar to 30 min) subjects were either exposed or sham-exposed to f ields (double-blinded) for 50 min. A second set of tests (employing alterna te versions) was administered 20 min from the start of this period. Each su bject returned after 7 days to repeat the sequence, but with the opposite f ield/sham status. Results and conclusions : The majority of the results indicated no signific ant effect of exposure on cognition. However, verbal recall of a list of 15 words after an interference (the different list) was significantly impaire d in the 'field on' condition. This is indicative of a reduction in short-t erm memory of words. The mean baseline score was somewhat higher in the 'fi eld on' condition. However, this difference is within the parameters of nor mal 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 per formance as a result of exposure to the 50 Hz field. This task requires exe cutive functioning with a working memory load, involving parietal spatial p rocessing coordinated by prefrontal executive processing. In summary, the d ata are suggestive of detrimental effects on cognitive processes, particula rly short-term learning and executive functioning. However, larger sample s izes are required to demonstrate statistically a more specific pattern of c ognitive effects.