scholarly journals Prospects for transcranial temporal interference stimulation in humans: a computational study

2019 ◽  
Author(s):  
Sumientra Rampersad ◽  
Biel Roig-Solvas ◽  
Mathew Yarossi ◽  
Praveen P. Kulkarni ◽  
Emiliano Santarnecchi ◽  
...  
Keyword(s):  
Electric Fields ◽  
Computational Study ◽  
Human Head ◽  
Element Model ◽  
Brain Regions ◽  
Relative Strength ◽  
Human Model ◽  
Head Model ◽  
Direct Stimulation ◽  
Field Strengths

AbstractTranscranial alternating current stimulation (tACS) is a noninvasive method used to modulate activity of superficial brain regions. Deeper and more steerable stimulation could potentially be achieved using transcranial temporal interference stimulation (tTIS): two high-frequency alternating fields interact to produce a wave with an envelope frequency in the range thought to modulate neural activity. Promising initial results have been reported for experiments with mice. In this study we aim to better understand the electric fields produced with tTIS and examine its prospects in humans through simulations with murine and human head models. A murine head finite element model was used to simulate previously published experiments of tTIS in mice. With a total current of 0.776 mA, tTIS electric field strengths up to 383 V/m were reached in the modeled mouse brain, affirming experimental results indicating that suprathreshold stimulation is possible in mice. Using a detailed anisotropic human head model, tTIS was simulated with systematically varied electrode configurations and input currents to investigate how these parameters influence the electric fields. An exhaustive search with 88 electrode locations covering the entire head (146M current patterns) was employed to optimize tTIS for target field strength and focality. In all analyses, we investigated maximal effects and effects along the predominant orientation of local neurons. Our results showed that it was possible to steer the peak tTIS field by manipulating the relative strength of the two input fields. Deep brain areas received field strengths similar to conventional tACS, but with less stimulation in superficial areas. Maximum field strengths in the human model were much lower than in the murine model, too low to expect direct stimulation effects. While field strengths from tACS were slightly higher, our results suggest that tTIS is capable of producing more focal fields and allows for better steerability. Finally, we present optimal four-electrode current patterns to maximize tTIS in regions of the pallidum (0.37 V/m), hippocampus (0.24 V/m) and motor cortex (0.57 V/m).

scholarly journals A Software Toolkit for TMS Electric-Field Modeling with Boundary Element Fast Multipole Method: An Efficient MATLAB Implementation

2020 ◽  
Author(s):  
Sergey N. Makarov ◽  
William A. Wartman ◽  
Mohammad Daneshzand ◽  
Kyoko Fujimoto ◽  
Tommi Raij ◽  
...  
Keyword(s):  
High Resolution ◽  
Boundary Element ◽  
Electric Fields ◽  
Fast Multipole Method ◽  
Human Head ◽  
Head Model ◽  
Fast Multipole ◽  
Software Toolkit ◽  
Model Repository ◽  
Multipole Method

AbstractBackgroundTranscranial magnetic stimulation (TMS) is currently the only non-invasive neurostimulation modality that enables painless and safe supra-threshold stimulation by employing electromagnetic induction to efficiently penetrate the skull. Accurate, fast, and high resolution modeling of the electric fields (E-fields) may significantly improve individualized targeting and dosing of TMS and therefore enhance the efficiency of existing clinical protocols as well as help establish new application domains.ObjectiveTo present and disseminate our TMS modeling software toolkit, including several new algorithmic developments, and to apply this software to realistic TMS modeling scenarios given a high-resolution model of the human head including cortical geometry and an accurate coil model.MethodThe recently developed charge-based boundary element fast multipole method (BEM-FMM) is employed as an alternative to the 1st order finite element method (FEM) most commonly used today. The BEM-FMM approach provides high accuracy and unconstrained field resolution close to and across cortical interfaces. Here, the previously proposed BEM-FMM algorithm has been improved in several novel ways.Results and ConclusionsThe improvements resulted in a threefold increase in computational speed while maintaining the same solution accuracy. The computational code based on the MATLAB® platform is made available to all interested researchers, along with a coil model repository and examples to create custom coils, head model repository, and supporting documentation. The presented software toolkit may be useful for post-hoc analyses of navigated TMS data using high-resolution subject-specific head models as well as accurate and fast modeling for the purposes of TMS coil/hardware development.

scholarly journals tACS entrains neural activity while somatosensory input is blocked

2019 ◽  
Author(s):  
Pedro G. Vieira ◽  
Matthew R. Krause ◽  
Christopher C. Pack
Keyword(s):  
Electric Fields ◽  
Neural Activity ◽  
Alternative Hypothesis ◽  
Brain Regions ◽  
Nerve Fibers ◽  
Great Promise ◽  
Direct Stimulation ◽  
Topical Anesthetic ◽  
Somatosensory Stimulation ◽  
Somatosensory Input

AbstractTranscranial alternating current stimulation (tACS) modulates brain activity by passing electrical current through electrodes that are attached to the scalp. Because it is safe and non-invasive, it holds great promise as a tool for basic research and clinical treatment. However, little is known about how tACS ultimately influences neural activity. One hypothesis is that tACS affects neural responses directly, by producing electrical fields that interact with the brain’s endogenous electrical activity. Since the shape and location of these electric fields can be controlled, stimulation could be targeted at brain regions associated with particular behaviors or symptoms. However, an alternative hypothesis is that tACS affects neural activity indirectly, via peripheral sensory afferents. In particular, it has often been hypothesized that tACS acts on nerve fibers in the skin, which in turn provide rhythmic input to central neurons. In this case, there would be little possibility of targeted brain stimulation, as the regions modulated by tACS would depend entirely on the somatosensory pathways originating in the skin around the stimulating electrodes. Here, we directly test these competing hypotheses by recording single-unit activity in the hippocampus and visual cortex of monkeys receiving tACS. We find that tACS entrains neuronal activity in both regions, so that cells fire synchronously with the stimulation. Blocking somatosensory input with a topical anesthetic does not significantly alter these neural entrainment effects. These data are therefore consistent with the direct stimulation hypothesis and suggest that peripheral somatosensory stimulation is not required for tACS to entrain neurons.

scholarly journals Temporal interference stimulation targets deep brain regions by modulating neural oscillations

2019 ◽  
Author(s):  
Zeinab Esmaeilpour ◽  
Greg Kronberg ◽  
Davide Reato ◽  
Lucas C Parra ◽  
Marom Bikson
Keyword(s):  
Electric Fields ◽  
Modulation Frequency ◽  
Hippocampal Slices ◽  
Human Head ◽  
Gamma Oscillations ◽  
Brain Regions ◽  
Neural Oscillations ◽  
Neuronal Membrane ◽  
Underlying Mechanisms ◽  
Deep Brain

AbstractTemporal interference (TI) stimulation of the brain generates amplitude-modulated electric fields oscillating in the kHz range. A validated current-flow model of the human head estimates that amplitude-modulated electric fields are stronger in deep brain regions, while unmodulated electric fields are maximal at the cortical regions. The electric field threshold to modulate carbachol-induced gamma oscillations in rat hippocampal slices was determined for unmodulated 0.05-2 kHz sine waveforms, and 5 Hz amplitude-modulated waveforms with 0.1-2 kHz carrier frequencies. The neuronal effects are replicated with a computational network model to explore the underlying mechanisms. Experiment and model confirm the hypothesis that spatial selectivity of temporal interference stimulation depends on the phasic modulation of neural oscillations only in deep brain regions. This selectivity is governed by network adaption (e.g. GABAb) that is faster than the amplitude-modulation frequency. The applied current required depends on the neuronal membrane time-constant (e.g. axons) approaching the kHz carrier frequency of temporal interference stimulation.

Effects of Attached Body on Biomechanical Response of the Helmeted Human Head Under Blast

2013 ◽  
Author(s):  
M. Salimi Jazi ◽  
A. Rezaei ◽  
G. Karami ◽  
F. Azarmi ◽  
M. Ziejewski
Keyword(s):  
Boundary Conditions ◽  
Blast Wave ◽  
Computational Study ◽  
Human Head ◽  
Blast Waves ◽  
The Body ◽  
Head Model ◽  
Mechanical Responses ◽  
Dynamic Nonlinear Analysis ◽  
Head Neck

The results of a computational study on the effect of the body on biomechanical responses of a helmeted human head under various blast load orientations are presented in this work. The focus of the work is to study the effects of the human head model boundary conditions on mechanical responses of the head such as variations of intracranial pressure (ICP). In this work, finite element models of the helmet, padding system, and head components are used for a dynamic nonlinear analysis. Appropriate contacts and conditions are applied between different components of the head, pads and helmet. Blast is modeled in a free space. Two different blast wave orientations with respect to head position are set, so that, blast waves tackle the front and back of the head. Standard trinitrotoluene is selected as the high explosive (HE) material. The standoff distance in all cases is one meter from the explosion site and the mass of HE is 200 grams. To study the effect of the body, three different boundary conditions are considered; the head-neck model is free; the base of the neck is completely fixed; and the head-neck model is attached to the body. Comparing the results shows that the level of ICP and shear stress on the brain are similar during the first five milliseconds after the head is hit by the blast waves. It explains the fact that the rest of the body does not have any contribution to the response of the head during the first 5 milliseconds. However, the conclusion is just reasonable for the presented blast situations and different blast wave incidents as well as more directions must be considered.

scholarly journals Multi-channel transorbital electrical stimulation for effective stimulation of posterior retina

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sangjun Lee ◽  
Jimin Park ◽  
Jinuk Kwon ◽  
Dong Hwan Kim ◽  
Chang-Hwan Im
Keyword(s):  
Electrical Stimulation ◽  
Electric Field ◽  
Electric Fields ◽  
Anterior Part ◽  
Posterior Part ◽  
Human Head ◽  
Electrical Current ◽  
Field Analysis ◽  
Head Model ◽  
Stimulation Of

AbstractTransorbital electrical stimulation (tES) has been studied as a new noninvasive method for treating intractable eye diseases by delivering weak electrical current to the eye through a pair of electrodes attached to the skin around the eye. Studies have reported that the therapeutic effect of tES is determined by the effective stimulation of retinal cells that are densely distributed in the posterior part of the retina. However, in conventional tES with a pair of electrodes, a greater portion of the electric field is delivered to the anterior part of the retina. In this study, to address this issue, a new electrode montage with multiple electrodes was proposed for the effective delivery of electric fields to the posterior retina. Electric field analysis based on the finite element method was performed with a realistic human head model, and optimal injection currents were determined using constrained convex optimization. The resultant electric field distributions showed that the proposed multi-channel tES enables a more effective stimulation of the posterior retina than the conventional tES with a pair of electrodes.

Skull Deformation Has No Impact on the Variation of Brain Intracranial Pressure

2016 ◽  
Author(s):  
Asghar Rezaei ◽  
Hesam Sarvghad-Moghaddam ◽  
Ashkan Eslaminejad ◽  
Mariusz Ziejewski ◽  
Ghodrat Karami
Keyword(s):  
Intracranial Pressure ◽  
Brain Injuries ◽  
Computational Study ◽  
Human Head ◽  
Body Motion ◽  
Stress Wave Propagation ◽  
Head Model ◽  
The Impact ◽  
The Brain ◽  
Skull Deformation

Skull deformation and vibration has been hypothesized to be an injury mechanism when the human head undergoes an impact scenario. The extent that skull deformation may increase the risk of traumatic brain injury, however, is not well understood. This computational study explains whether skull deformation has any impact on the variation of intracranial pressure (ICP). To this end, a finite element head model including major anatomical components of the human head was employed. The head model has been validated against ICP variations on the brain. The impact simulations were carried out using a rigid cylindrical impactor. The scenarios were frontal impacts with the impactor hitting the forehead of the head model at two impact severity levels. In order to examine the effect of skull elasticity on the stress wave propagation inside the cranium under an external applied force, the skull was also taken as a rigid body with the same density as the elastic one, and the result were compared with those obtained with the deformable skull. For the two cases, the variation of ICPs at the coup and countercoup sites were recorded and compared. The results of the study showed that, for the case studies presented here, the deformation of skull didn’t increase the level of ICP inside the brain. It was concluded that the skull rapid body motion might be responsible for brain injuries.

scholarly journals Effects of transcranial alternating current stimulation on spiking activity in computational models of single neocortical neurons

2021 ◽  
Author(s):  
Harry Tran ◽  
Sina Shirinpour ◽  
Alexander Opitz
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Pyramidal Neurons ◽  
Computational Study ◽  
Experimental Studies ◽  
Alternating Current ◽  
Oscillatory Activity ◽  
Transcranial Alternating Current Stimulation ◽  
Spiking Activity ◽  
Field Strengths

AbstractNeural oscillations are a key mechanism for information transfer in brain circuits. Rhythmic fluctuations of local field potentials control spike timing through cyclic membrane de- and hyperpolarization. Transcranial alternating current stimulation (tACS) is a non-invasive neuromodulation method which can directly interact with brain oscillatory activity by imposing an oscillating electric field on neurons. Despite its increasing use, the basic mechanisms of tACS are still not fully understood. Here, we investigate in a computational study the effects of tACS on morphologically realistic neurons with ongoing spiking activity. We characterize the membrane polarization as a function of electric field strength and subsequent effects on spiking activity in a set of 25 neurons from different neocortical layers. We find that tACS does not affect the firing rate of investigated neurons for electric field strengths applicable to human studies. However, we find that the applied electric fields entrain the spiking activity of large pyramidal neurons at < 1mV/mm field strengths. Our model results are in line with recent experimental studies and can provide a mechanistic framework to understand the effects of oscillating electric fields on single neuron activity. They highlight the importance of neuron morphology in responsiveness to electrical stimulation and suggest that large pyramidal neurons are most likely the prime target for tACS.

Computational models of Bitemporal, Bifrontal and Right Unilateral ECT predict differential stimulation of brain regions associated with efficacy and cognitive side effects

2017 ◽  
Vol 41 (1) ◽  
pp. 21-29 ◽  
Author(s):  
S. Bai ◽  
V. Gálvez ◽  
S. Dokos ◽  
D. Martin ◽  
M. Bikson ◽  
...  
Keyword(s):  
Side Effects ◽  
Computational Models ◽  
Computational Modelling ◽  
Human Head ◽  
Distribution Patterns ◽  
Brain Regions ◽  
Electrode Placement ◽  
Direct Stimulation ◽  
Cognitive Side Effects ◽  
Stimulation Of

AbstractBackgroundExtensive clinical research has shown that the efficacy and cognitive outcomes of electroconvulsive therapy (ECT) are determined, in part, by the type of electrode placement used. Bitemporal ECT (BT, stimulating electrodes placed bilaterally in the frontotemporal region) is the form of ECT with relatively potent clinical and cognitive side effects. However, the reasons for this are poorly understood.ObjectiveThis study used computational modelling to examine regional differences in brain excitation between BT, Bifrontal (BF) and Right Unilateral (RUL) ECT, currently the most clinically-used ECT placements. Specifically, by comparing similarities and differences in current distribution patterns between BT ECT and the other two placements, the study aimed to create an explanatory model of critical brain sites that mediate antidepressant efficacy and sites associated with cognitive, particularly memory, adverse effects.MethodsHigh resolution finite element human head models were generated from MRI scans of three subjects. The models were used to compare differences in activation between the three ECT placements, using subtraction maps.Results and conclusionIn this exploratory study on three realistic head models, Bitemporal ECT resulted in greater direct stimulation of deep midline structures and also left temporal and inferior frontal regions. Interpreted in light of existing knowledge on depressive pathophysiology and cognitive neuroanatomy, it is suggested that the former sites are related to efficacy and the latter to cognitive deficits. We hereby propose an approach using binarised subtraction models that can be used to optimise, and even individualise, ECT therapies.

The Construction and Validation of a Finite Element Human Head Model for Skull Fracture

2014 ◽  
Vol 934 ◽  
pp. 20-25
Author(s):  
Dan Wang ◽  
Xue Wei Song ◽  
Xiao Yan Sun ◽  
Zhi Jun Du ◽  
Jun Yuan Zhang ◽  
...  
Keyword(s):  
Finite Element ◽  
Male Volunteer ◽  
Skull Fracture ◽  
Ct Scanning ◽  
Human Head ◽  
Element Model ◽  
Head Model ◽  
Good Consistency ◽  
The Impact ◽  
Chinese Male

In this paper, a finite element model of human head was established based on CT scanning on a 40-year-old and 50 percentile Chinese male volunteer, and the model was verified with the experiment conducted by Verschueren and skull fracture was investigated during the collision. The frontal of head was impacted with different velocities during the impact tests. A break-deletion element process was represented to simulate the pathological phenomena of skull fracture.The results showed that the simulation results and experimental results were in a good consistency on both mechanics and pathology.

scholarly journals Finite element head model for the crew injury assessment in a light armoured vehicle

2020 ◽  
Vol 22 (2) ◽  
Author(s):  
Michał Burkacki ◽  
Wojciech Wolański ◽  
Sławomir Suchoń ◽  
Kamil Joszko ◽  
Bożena Gzik-Zroska ◽  
...  
Keyword(s):  
Finite Element ◽  
Head Injury ◽  
Human Head ◽  
Element Model ◽  
Head Model ◽  
Dynamic Effects ◽  
Vehicle Model ◽  
Future Studies ◽  
Injury Assessment

Purpose: The aim of this paper was the development of a finite element model of the soldier’s head to assess injuries suffered by soldiers during blast under a light armoured vehicle. Methods: The application of a multibody wheeled armoured vehicle model, including the crew and their equipment, aenabled the researchers to analyse the most dangerous scenarios of the head injury. These scenarios have been selected for a detailed analysis using the finite element head model which allowed for the examination of dynamic effects on individual head structures. In this paper, the authors described stages of the development of the anatomical finite element head model. Results: The results of the simulations made it possible to assess parameters determining the head injury of the soldier during the IED explosion. The developed model allows the determination of the parameters of stress, strain and pressure acting on the structures of the human head. Conclusion: In future studies, the model will be used to carry out simulations which will improve the construction of the headgear in order to minimize the possibility of the head injury.

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