Mechanisms of Magnetic Stimulation of Central Nervous System Neurons

Abstract

Transcranial magnetic stimulation (TMS) is a stimulation method in which a magnetic coil generates a magnetic field in an area of interest in the brain. This magnetic field induces an electric field that modulates neuronal activity. The spatial distribution of the induced electric field is determined by the geometry and location of the coil relative to the brain. Although TMS has been used for several decades, the biophysical basis underlying the stimulation of neurons in the central nervous system (CNS) is still unknown. To address this problem we developed a numerical scheme enabling us to combine realistic magnetic stimulation (MS) with compartmental modeling of neurons with arbitrary morphology. The induced electric field for each location in space was combined with standard compartmental modeling software to calculate the membrane current generated by the electromagnetic field for each segment of the neuron. In agreement with previous studies, the simulations suggested that peripheral axons were excited by the spatial gradients of the induced electric field. In both peripheral and central neurons, MS amplitude required for action potential generation was inversely proportional to the square of the diameter of the stimulated compartment. Due to the importance of the fiber's diameter, magnetic stimulation of CNS neurons depolarized the soma followed by initiation of an action potential in the initial segment of the axon. Passive dendrites affect this process primarily as current sinks, not sources. The simulations predict that neurons with low current threshold are more susceptible to magnetic stimulation. Moreover, they suggest that MS does not directly trigger dendritic regenerative mechanisms. These insights into the mechanism of MS may be relevant for the design of multi-intensity TMS protocols, may facilitate the construction of magnetic stimulators, and may aid the interpretation of results of TMS of the CNS.

Spike-frequency adaptation of a two-compartment neuron modulated by extracellular electric fields

“…Although there are widespread applications of electromagnetic stimulation in cognitive research and disease treatment, many questions still remain about the mechanisms underlying the neuromodulation by electromagnetic fields (Wagner et al 2007;Peterchev et al 2012). It has been shown that the basic principle for these noninvasive techniques is that they induce an extracellular electric field around the brain tissue of interest to modulate corresponding neuronal activity and behavior (Peterchev et al 2012;Pashut et al 2011). Therefore, exploration of the neuromodulatory mechanism of electromagnetic fields requires knowledge of how an induced extracellular electric field interacts with and modifies neuronal dynamics (Peterchev et al 2012).…”

Modelling Dispersive Behavior of Excitable Cells

“…Since these criteria depend on the geometry of stimulators, most researchers do not introduce the best stimulator, but the results can be helpful in future designs [5][6][7][8][9]. Obtaining the thresholds of excitability, which depends on the stimulator parameters, is common in the literature [4,[10][11][12][13][14][15]. In all of these pieces of research, diagrams such as excitability thresholds and parameter impact are determined to help the design of stimulators and cognition of excitable cells.…”

Synchronization of neuron population subject to steady DC electric field induced by magnetic stimulation

“…Clinical evidences point out that magnetic field can induce an electrical field that modulates neuronal activity of special brain tissue (Legros et al 2010;Cook et al 2004). For example, transcranial magnetic stimulation (TMS) can disrupt or induce activity in a particular brain tissue (Pashut et al 2011;Kamitani 2011). It provides a valuable tool to map brain function, such as motor and sensory processes, attention, memory, language, and neuronal plasticity (Di Lazzaro et al 2004;Lisanby et al 2000;Terao and Ugawa 2002;Ziemann and Rothwell 2000).…”