Computational analysis of non-invasive deep brain stimulation based on interfering electric fields

Abstract

Neuromodulation modalities are used as effective treatments for some brain disorders. Non-invasive deep brain stimulation (NDBS) via temporally interfering electric fields has emerged recently as a non-invasive strategy for electrically stimulating deep regions in the brain. The objective of this study is to provide insight into the fundamental mechanisms of this strategy and assess the potential uses of this method through computational analysis. Analytical and numerical methods are used to compute the electric potential and field distributions generated during NDBS in homogeneous and inhomogeneous models of the brain. The computational results are used for specifying the activated area in the brain (macroscopic approach), and quantifying its relationships to the stimulation parameters. Two automatic algorithms, using artificial neural network (ANN), are developed for the homogeneous model with two and four electrode pairs to estimate stimulation parameters. Additionally, the extracellular potentials are coupled to the compartmental axon cable model to determine the responses of the neurons to the modulated electric field in two developed models and to evaluate the precise activated area location (microscopic approach). Our results show that although the shape of the activated area was different in macroscopic and microscopic approaches, it located only at depth. Our optimization algorithms showed significant accuracy in estimating stimulation parameters. Moreover, it demonstrated that the more the electrode pairs, the more controllable the activated area. Finally, compartmental axon cable modeling results verified that neurons can demodulate and follow the electric field modulation envelope amplitude (MEA) in our models. The results of this study help develop the NDBS method and eliminate some limitations associated with the nonautomated optimization algorithm.

Biophysics of Temporal Interference Stimulation

“…This approach was termed temporal interference (TI) (Grossman et al, 2017) and had been proposed decades earlier under different names, such as interferential current therapy and interferential stimulation (Agharezaee and Mahnam, 2015;Goats, 1990). Translating these pivotal studies into successful clinical therapies requires an understanding of how TI fields are modulated within the human body (Cao and Grover, 2020;Karimi et al, 2019;Rampersad et al, 2019). In consequence, there is an ongoing healthy debate examining the clinical utility of this technology when considering the challenge of inefficient current penetration in large structures, such as the human head (Cao and Grover, 2018; Howell and McIntyre, 2020; Rampersad et al, 2019).…”

Improving the Effect of Transcranial Alternating Current Stimulation (tACS): A Systematic Review

“…In addition, because different neurons have different excitability, the interaction between these neurons and extracellular stimulation is complex. Therefore, the biological mechanism of neuroregulatory methods such as tACS is not completely clear (Cubo et al, 2018 ), and many factors need to be analyzed to understand the effect of a given brain stimulation approach (Karimi et al, 2019 ). Therefore, this section summarizes the computer simulation results of electrode parameters, high-definition electrical stimulation, and interference modulation stimulation.…”

“…Studies have shown that only focus montages such as circular montages or high-definition montages can specifically manipulate the phase relationship between two target regions without injecting unwanted electric fields into other regions (Saturnino et al, 2017 ; Karabanov et al, 2019 ). Moreover, the more electrode pairs there are, the more the activation region can be targeted accurately (Karimi et al, 2019 ). Compared with the classical electrode montage, the ring electrode montage can stimulate the target region more intensively and significantly reduce neurosensory side effects (Heise et al, 2016 ).…”

Focusing the temporally interfering electric fields in non‐invasive deep brain stimulation

“…Second, by a simple electrostatic analysis, it can be shown that the vanishes on the y ‐axis. Thus where can be obtained from the classic modal solution of (1 ) based on the methods of separation of variables, as reported in [20 ]. Noting that all of the quantities in (4 ) are real‐valued, minimising (maximising) of (4 ) is equivalent to minimising (maximising) of .…”

“…To date, no regularised procedure is introduced to focus the amplitude‐modulated (AM) electric field at the desired location even from the mathematical standpoint at the simulation level. In [20 ], some algorithms were developed to precisely locate the activated region in a homogeneous brain model for TI electrical fields produced by two and four electrode pairs. Though, they have not proposed any solution to increase the spatial resolution.…”