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. 2013 Apr 11;7:34.
doi: 10.3389/fncom.2013.00034. eCollection 2013.

Neural Mass Modeling of Power-Line Magnetic Fields Effects on Brain Activity

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Free PMC article

Neural Mass Modeling of Power-Line Magnetic Fields Effects on Brain Activity

J Modolo et al. Front Comput Neurosci. .
Free PMC article

Abstract

Neural mass models are an appropriate framework to study brain activity, combining a high degree of biological realism while being mathematically tractable. These models have been used, with a certain success, to simulate brain electric (electroencephalography, EEG) and metabolic (functional magnetic resonance imaging, fMRI) activity. However, concrete applications of neural mass models have remained limited to date. Motivated by experimental results obtained in humans, we propose in this paper a neural mass model designed to study the interaction between power-line magnetic fields (MFs) (60 Hz in North America) and brain activity. The model includes pyramidal cells; dendrite-projecting, slow GABAergic neurons; soma-projecting, fast GABAergic neurons; and glutamatergic interneurons. A simple phenomenological model of interaction between the induced electric field and neuron membranes is also considered, along with a model of post-synaptic calcium concentration and associated changes in synaptic weights Simulated EEG signals are produced in a simple protocol, both in the absence and presence of a 60 Hz MF. These results are discussed based on results obtained previously in humans. Notably, results highlight that (1) EEG alpha (8-12 Hz) power can be modulated by weak membrane depolarizations induced by the exposure; (2) the level of input noise has a significant impact on EEG power modulation; and (3) the threshold value in MF flux density resulting in a significant effect on the EEG depends on the type of neuronal populations modulated by the MF exposure. Results obtained from the model shed new light on the effects of power-line MFs on brain activity, and will provide guidance in future human experiments. This may represent a valuable contribution to international regulation agencies setting guidelines on MF values to which the general public and workers can be exposed.

Keywords: brain stimulation; electroencephalogram (EEG); neural mass models; power-line magnetic fields; synaptic plasticity.

Figures

Figure 1
Figure 1
Proposed extension of the Sotero et al. model of cortical dynamics (figure modified from (Sotero and Trujillo-Barreto, 2008); with permission). The inclusion of the new population of fast GABAergic neurons and its connectivity with other neuronal populations is highlighted in red.
Figure 2
Figure 2
Example of neurophysiological signals (EEG, post-synaptic calcium concentration, synaptic weight) simulated using the model, both without and with exposure to a 60 Hz MF.
Figure 3
Figure 3
(A–D): Spectral power in the EEG alpha (8–12 Hz) band as a function of the MF-induced membrane polarization dV; before (blue), during (red) and after (blue) the 1-h 60 Hz MF exposure period. (A) dV = 125 μV; (B), dV = 250 μV; (C) dV = 500 μV; (D) dV = 1000 μV. A decrease in EEG alpha power is observed as the value of dV (proportional to the MF flux density) increases. (E) Example of average power spectrum before, during and after exposure to the 60 Hz MF, for dV = 500 μV.
Figure 4
Figure 4
Effect of the input noise level variance on EEG alpha power modulation caused by the 60 Hz MF exposure in the presence of the simplified synaptic plasticity model. Noise variance σ was varied as follows: yellow, 120 spikes/s; orange: 150 spikes/s; red, 180 spikes/s; blue: 210 spikes/s. The value of dV was fixed to 500 μV in all simulations. The EEG alpha power is presented for each noise variance value before, during and after 60 Hz MF exposure. The impact of the 60 Hz MF exposure on EEG alpha power decreases with increased input noise amplitude, likely since the weak 60 Hz membrane potential perturbation becomes “buried” in noise.
Figure 5
Figure 5
Effect of synaptic plasticity on EEG alpha power modulation by 60 Hz MF exposure compared to the case where synaptic plasticity is not taken into account. The conditions are Before, During, and After 60 Hz MF exposure, with (1, 3, 5) and without (2, 4, 6) synaptic plasticity. (A) dV = 125 μV; (B) dV = 250 μV; (C) dV = 500 μV; (D) dV = 1000 μV.
Figure 6
Figure 6
Effect of the 60 Hz MF exposure on EEG alpha power depending on which populations of neurons are modulated by the induced electric field. The exposure protocol is the same than previously (1-h exposure, with 30 min before and after without exposure). The maximal value of the MF-induced membrane depolarization was dV = 1 mV. Pyramidal neurons are considered to be modulated in each scenario. Pyr, pyramidal neurons only; slow+fast, pyramidal neurons, slow and fast GABAergic interneurons; slow, pyramidal neurons, slow GABAergic neurons; fast, pyramidal neurons, fast GABAergic neurons.
Figure 7
Figure 7
MF flux density curves as a function of the MF-induced membrane depolarization dV, computed for different values of the polarization time constant τ. The input noise variance to the model was taken as 180 spikes/s. Different noise variance values will result in different MF threshold curves.
Figure A1
Figure A1
Function Ω used in our model as a piecewise-linear approximation of the function used by Shouval et al. (2002b), preserving the main properties of this function, i.e., the level of post-synaptic calcium concentration regulating LTP and LTD processes.

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