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. 2015 Jul 27;10(7):e0132024.
doi: 10.1371/journal.pone.0132024. eCollection 2015.

Effects of a 60 Hz Magnetic Field Exposure Up to 3000 μT on Human Brain Activation as Measured by Functional Magnetic Resonance Imaging

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Free PMC article

Effects of a 60 Hz Magnetic Field Exposure Up to 3000 μT on Human Brain Activation as Measured by Functional Magnetic Resonance Imaging

Alexandre Legros et al. PLoS One. .
Free PMC article

Abstract

Several aspects of the human nervous system and associated motor and cognitive processes have been reported to be modulated by extremely low-frequency (ELF, < 300 Hz) time-varying Magnetic Fields (MF). Due do their worldwide prevalence; power-line frequencies (60 Hz in North America) are of particular interest. Despite intense research efforts over the last few decades, the potential effects of 60 Hz MF still need to be elucidated, and the underlying mechanisms to be understood. In this study, we have used functional Magnetic Resonance Imaging (fMRI) to characterize potential changes in functional brain activation following human exposure to a 60 Hz MF through motor and cognitive tasks. First, pilot results acquired in a first set of subjects (N=9) were used to demonstrate the technical feasibility of using fMRI to detect subtle changes in functional brain activation with 60 Hz MF exposure at 1800 μT. Second, a full study involving a larger cohort of subjects tested brain activation during 1) a finger tapping task (N=20), and 2) a mental rotation task (N=21); before and after a one-hour, 60 Hz, 3000 μT MF exposure. The results indicate significant changes in task-induced functional brain activation as a consequence of MF exposure. However, no impact on task performance was found. These results illustrate the potential of using fMRI to identify MF-induced changes in functional brain activation, suggesting that a one-hour 60 Hz, 3000 μT MF exposure can modulate activity in specific brain regions after the end of the exposure period (i.e., residual effects). We discuss the possibility that MF exposure at 60 Hz, 3000 μT may be capable of modulating cortical excitability via a modulation of synaptic plasticity processes.

Conflict of interest statement

Competing Interests: Funder of the authors' study include Electricité de France, Réseau de Transport d’Electricité and Hydro-Québec. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Time course of experiment.
Sequence of imaging and testing periods, including one hour of control or 60 Hz MF exposure to a 60 Hz MF at 3000 μT during one hour.
Fig 2
Fig 2. Magnetic field gradient.
The maximal MF level was obtained at the cortical level. The variation of the MF intensity depends on the position along the bore Z-axis and is shown in red. The MF intensity delivered by the gradient coil linearly decreases to reach zero at the isocentre (at the level of the first cervical vertebrae).
Fig 3
Fig 3. Functional brain activation—primary somatosensory cortex (S1).
S1: Top row—Tapping: pre-exposure group image (N = 9). Middle row—Tapping: post- minus pre-exposure condition (control, N = 5). Bottom row—Tapping: post- minus pre-exposure condition (60 Hz MF, N = 4). Results centered on the point of Talairach coordinates (X = -40, Y = -31, Z = 52).
Fig 4
Fig 4. Functional brain activation—anterior cingulate cortex.
AC: Top row—Tapping: pre-exposure group image (N = 9). Middle row—Tapping: post- minus pre-exposure condition (control, N = 5). Bottom row—Tapping: post- minus pre-exposure condition (60 Hz MF, N = 4). Results centered on the point of Talairach coordinates (X = -7, Y = -6, Z = 39).
Fig 5
Fig 5. Functional brain activation—cerebellum.
Cerebellum: Top row—Tapping: pre- exposure group image (N = 9). Middle row—Tapping: post- minus pre-exposure condition (control, N = 5). Bottom row—Tapping: post- minus pre-exposure condition (60 Hz MF, N = 4).
Fig 6
Fig 6. Pre-exposure finger tapping averaged activation map of the contralateral motor cortex regions (top row) and the ipsilateral cerebellum (bottom row) for 20 participants for the full study at 3000 μT.
The contralateral motor cortex images (top row) presented are centered on the Talairach coordinates corresponding to S1 (x = -41, y = -31, z = 53) for the motor cortex region. The ipsilateral cerebellum images (bottom row) presented are centered on the Talairach coordinates corresponding to the anterior lobe of the ipsilateral cerebellum (x = 18, 7 = -47, z = -15).
Fig 7
Fig 7. Increased activation in S1 in the 60 Hz MF exposure group.
*(All images were normalized in Talairach space—BrainVoyager GLM analysis). Results centered on the point of Talairach coordinates (X = -40, Y = -31, Z = 52). Fig 7. Top) Pre-exposure activation and deactivation for all subjects (N = 20). Fig 7. Middle) Post—minus- pre control exposure (N = 11). Fig 7. Bottom) Post- minus- pre 60 Hz MF exposure (N = 9).
Fig 8
Fig 8. Increased activation in the anterior lobe of the ipsilateral cerebellum in the 60 Hz MF exposure group (All images were normalized in Talairach space—BrainVoyager GLM analysis).
Results centered on the point of Talairach coordinates (X = 18, Y = -47, Z = -15). Fig 8. Top) Pre-exposure activation and deactivation for all subjects (N = 20). Fig 8. Middle) Post-minus-pre control exposure (N = 11). Fig 8. Bottom) Post-minus-pre 60 Hz MF exposure (N = 9).
Fig 9
Fig 9. Activation in the posterior cingulate during the mental rotation task.
Top) Pre-exposure (N = 21); Middle) Post- minus pre- exposure in the control group (N = 11); Bottom) Post- minus pre- exposure in the 60 Hz MF exposure group (N = 10). Results centered on the point of Talairach coordinates (X = -5, Y = -53, Z = 16).
Fig 10
Fig 10. Activation in the left intraparietal sulcus during the mental rotation task.
Top) Pre-exposure (N = 21); Middle) Post- minus pre- exposure in the control group (N = 11); Bottom) Post- minus pre- exposure in the 60 Hz MF exposure group (N = 10). Results centered on the point of Talairach coordinates (X = -30, Y = -84, Z = 18).
Fig 11
Fig 11. Activation in the right occipital cortex during the mental rotation task.
Top) Pre-exposure (N = 21); Middle) Post- minus pre- exposure in the control group (N = 11); Bottom) Post- minus pre- exposure in the 60 Hz MF exposure group (N = 10). Results centered on the point of Talairach coordinates (X = 27, Y = -59, Z = -23).
Fig 12
Fig 12. Time series of the magnetic induction measured during the 60 Hz and BOLD sequences.
Fig 13
Fig 13. Comparison of the magnetic induction power spectrum for the 60 Hz and BOLD sequences.

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