Effect of low-frequency magnetic fields on brain electrical activity in human subjects

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Abstract

Objective: To measure the response rate of normal human subjects to a low-strength, low-frequency magnetic field (MF), using nonlinear quantitative analysis of the electroencephalogram (EEG).

Methods: Eight subjects were exposed to a series of trials, each consisting of the application of the MF (1 G, 60 Hz) for 2 s followed by a field-free period of 5 s, and the EEG was analyzed statistically using phase-space methods to assess whether the subject detected the MF.

Results: Each subject exhibited statistically significant changes in the EEG during presentation of the MF, as evidenced by increases in percent determinism and percent recurrence, two different measures of deterministic structure in the recorded signal, thereby indicating that the MF had been detected.

Conclusions: The 100% response rate manifested by the study group suggested that the ability to detect low-strength, low-frequency MFs is a common property of the human nervous system.

Introduction

A deeper understanding of the changes in brain electrical activity produced during application of magnetic fields (MFs) is the goal of different lines of research including transcranial stimulation (TS) (Terao and Ugawa, 2002), and evaluation of the public-health significance of fields in the environment (Portier and Wolfe, 1998). The major unresolved issues regarding TS relate primarily to therapeutic consequences, because the detection process is reasonably well understood. For environmental MFs, however, which typically are 3 or more orders of magnitude smaller than those used for TS, the central question concerns whether the fields are actually detected by human subjects. Effects of low-strength MFs on brain electrical activity were found in some studies; for example, subjects exposed to 3 Hz, 1 G, and to 50 mG, pulsed at 6–20 Hz exhibited significantly reduced spectral power, on average (Schienle et al., 1996, Heusser et al., 1997). In another study, however, no average effect on spectral power was found after exposure to 100 mG, 60 Hz (Lyskov et al., 2001).

Mixed results also occurred when the effect of MFs on brain electrical activity was assessed within individual subjects. Exposure to 0.25–5.0 G, 35–40 Hz produced changes in the EEG in only 7 of 14 subjects (Bell et al., 1991). Application of 10–40 G DC altered the epileptiform spike activity in only 5 of 10 patients in the period immediately following application of the field (Dobson et al., 2000). Eleven subjects exposed to 0.8 G, 1.5–10 Hz exhibited increased spectral power, but 8 subjects exhibited no effect (Marino et al., 1996). These and other pertinent studies have been reviewed recently (Cook et al., 2002)

Various explanations could account for why MFs altered the EEG in some studies or subjects, but not others. The apparent inconsistencies could have arisen from inter-subject variations in sensitivity to the MF (Lyskov et al., 2001). The spectral properties of the MF may be important in determining its biological effect, with the result that field effects occur only within particular windows of frequency or field strength (Gartzke and Lange, 2002). Another possibility is that the absence of an effect in some subjects or some groups of subjects was due to a relative insensitivity of the methods used to analyze the EEG, which in all the previous studies were linear methods. Recent studies suggested that the EEG can exhibit nonlinear determinism (law-like behavior) due to low-dimensional chaotic sources (Krystal et al., 1996, Theiler and Rapp, 1996, Micheloyannis et al., 1998, Marino et al., 2002). An analytical approach that also took nonlinear effects into consideration might lead to a more consistent picture of the changes in brain electrical activity produced during application of MFs, possibly indicating that magnetodetection is a common human characteristic.

Our aim was to test the magnetodetection hypothesis by showing that detection of an arbitrary but environmentally relevant MF occurred in each subject in a representative test group. To accomplish this purpose, we compared the EEG within individual subjects obtained during the presence and the absence of the MF, using a novel method of analysis that was capable of capturing both linear and nonlinear effects that might be present (Marino, 2003).

Section snippets

Subjects

Eight clinically normal subjects were studied; their age in years and gender were 27/M, 34/F, 31/M, 18/F, 23/M, 45/F, 29/M, 28/F, for subjects 1–8, respectively. All procedures involving human subjects were reviewed and approved by the Institutional Review Board at our institution, including written informed consent. Scalp electrodes (Grass Instrument Co., Quincy, MA) were attached at C3, C4, P3, P4, O1, and O2 (International 10–20 system) and referred to linked ears; the ground was placed on

Results

Recurrence plots constructed from the EEG (Fig. 2) were similar to the complex two-dimensional patterns typical of physiological time series (Webber, 2003) and chaotic deterministic systems (Eckmann et al., 1987). The essential feature of the plots was that their texture resulted directly from the dynamical electrical activity of the brain; when the dynamical correlations in the EEG were reduced by randomizing the signal (Fig. 2B), the mean and standard deviation of the resulting signal were

Discussion

We assumed that a method of analyzing the EEG that did not parse its activity into linear and nonlinear parts but rather characterized the determinism actually present in the signal would facilitate detection of the effects of MFs. Based on that assumption, we used a novel analytical method (Marino, 2003) to compare the EEG within individual subjects in the presence and absence of the field. In each subject, %R and %D calculated from the occipital EEG at 120–310 ms from the onset of field

References (31)

  • J.P. Zbilut et al.

    Embeddings and delays as derived from quantification of recurrence plots

    Phys Lett A

    (1992)
  • G.B. Bell et al.

    Exposure system for the production of uniform magnetic fields

    J Bioelectricity

    (1989)
  • G.B. Bell et al.

    Frequency-specific blocking in the human brain caused by electromagnetic fields

    Neuroreport

    (1994)
  • M.R. Cook et al.

    A replication study of human exposure to 60-Hz fields: effects on neurobehavioral measures

    Bioelectromagnetics

    (1992)
  • C.M. Cook et al.

    Human electrophysiological and cognitive effects of exposure to ELF magnetic and ELF modulated RF and microwave fields: a review of recent studies

    Bioelectromagnetics

    (2002)

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