Abstract
Transcranial Electrical Stimulation (TES) continues to demonstrate success as a medical intervention for individuals with neurodegenerative diseases. Despite promising results from these neuromodulation modalities, the cellular level mechanisms by which this neurotherapy operates are not fully comprehended. In particular, the effects of TES on ion channel gating and ion transport are not known. Using the Poisson-Nernst-Planck model of electrodiffusion, coupled with a Hodgkin-Huxley based model of cellular ion transport, we present a model of TES that, for the first time, integrates electric potential energy, individualized ion species, voltage-gated ion channels, and transmembrane ionic flux during TES administration. Computational simulations are executed on a biologically-inspired domain with medically-based TES treatment parameters and quantify neuron-level electrical processes resulting from this form of neurostimulation. Results confirm prior findings that show that TES polarizes the cell membrane, however, these are extended as simulations in this paper show that polarization occurs in a location specific manner, where the type and degree of polarization depends on the position on the membrane within a node of Ranvier. In addition, results demonstrate that TES causes ion channel gating variables to change in a location specific fashion and, as a result, transmembrane current from distinct ion species depends on both time and membrane location. Another simulation finding is that intracellular calcium concentrations increase significantly due to a TES-induced calcium influx. As cytosolic calcium is critical in intracellular signaling pathways that govern proper neurotransmitter secretion as well as support cell viability, this alteration in calcium homeostasis suggests a possible mechanism by which TES operates at the neuronal level to achieve neurotherapeutic success.
Highlights
Transcranial electrical stimulation (TES) is a group of neurostimulation therapies that deliver low doses of electric current to targeted brain regions via noninvasive electrodes placed on a patient’s scalp
Of particular importance to applications focusing on neurodegenerative diseases, simulations of TES show calcium intracellular concentrations can increase by up to 71.65% along some regions of the node of Ranvier
This paper presents the first model of TES that incorporates neurophysiology with individual ion species and transmembrane ionic fluxes
Summary
Transcranial electrical stimulation (TES) is a group of neurostimulation therapies that deliver low doses of electric current to targeted brain regions via noninvasive electrodes placed on a patient’s scalp. The most common type of TES is transcranial direct current stimulation (tDCS), which administers a constant amount of electrical energy during therapy sessions. In addition to clinical findings, biological experiments have begun to show the effects of TES on membrane polarization (Liebetanz et al, 2002; Bikson et al, 2004; Stagg and Nitsche, 2011; Das et al, 2016) and calcium homeostasis (Islam et al, 1995; Nitsche et al, 2003; Adams et al, 2017), difficulties in capturing ion channel state, ionic flux, and intracellular calcium concentrations continuously over time with a high sampling frequency yields limited neurostimulation data at the cellular level (Adams et al, 2017). The direct influence of an applied TES electric current on voltage-gated ion channel states as well as other cellular level mechanism by which TES operates is largely unknown (Nitsche et al, 2008)
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