Numerical analysis of recurrence plots to detect effect of environmental-strength magnetic fields on human brain electrical activity.

Environmental magnetic fields may activate the neuroendocrine stressor system leading to some human diseases. The stressor theory predicts that the fields can trigger changes in brain electrical activity, like known stressors. We exposed subjects to 1 and 5 μT, 60 Hz while recording electroencephalograms (EEGs) from six derivations, and used a novel method based on numerical analysis of recurrence plots computed from the signals to detect brain electrical potentials evoked by onset and/or offset of the field. The EEGs were also analyzed using linear methods (time averaging). Evoked potentials occurred in all 22 subjects (family-wise error rate less than 0.05 for each subject); the average latency was 250 ms, as expected based on earlier studies using stronger magnetic fields. Field-induced changes in brain electrical activity were not found using time averaging. Control procedures and measurements obtained from electrical phantoms reasonably excluded recording artifacts or chance as explanations for the effects. Onset and offset of magnetic fields produced immediate changes in brain electrical activity, suggesting that the fields were detected by sensory transduction, like ordinary somatic stressors.