Selective stimulation of rat sciatic nerve using an array of mm‐size magnetic coils: a simulation study

Kosta, Pragya; Warren, David J.; Lazzi, Gianluca

doi:10.1049/htl.2018.5020

Cited by 9 publications

(9 citation statements)

References 25 publications

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“…The first would be to include a threshold for DTDI (e.g., DTDI ≥ 0.75) as a precautionary measure when individualizing the current dose. We recommend this value because studies pertaining to peripheral nerve stimulation have also found that such a threshold value (≥ 0.75) for the ‘selectivity index’ could ensure that the targeted region of the nerve is well activated [ 28 , 30 ]. While this may narrow down the suitability of subjects, such inclusion criteria could reduce the variability of tDCS.…”

Section: Discussionmentioning

confidence: 99%

“…It has been found that some brain regions may act as conduits, clustering most of the current to a specific location that can deter the intensity of the stimulation expected at the target ROI [ 6 , 26 ]. At this point, it is important to mention that other stimulation techniques (like peripheral nerve stimulation) are also intended to increase the stimulation intensity at target region while minimizing the stimulation received at non-target regions [ 27 , 28 , 29 , 30 ]. With tDCS, poor focality in stimulating the target region has constrained its efficacy.…”

Section: Introductionmentioning

confidence: 99%

“…With i-SATA(MNI), we introduce the dose–target determination index (DTDI), a simple estimate that will quantify the focality of stimulation and facilitate the selection of optimal current dose required to stimulate the target ROI in an individual’s brain. A similar metric defined as the ‘selectivity index’ that measures the recruitment of the targeted region compared to other non-targeted regions is used to quantify the effectiveness of peripheral nerve stimulation [ 27 , 28 , 29 , 30 ]. For tDCS, the DTDI will aim to provide a comprehensive overview of the intensity of the stimulation received by the target ROI and intermediary regions after a montage has been postprocessed in i-SATA(MNI).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Focality-Oriented Selection of Current Dose for Transcranial Direct Current Stimulation

Kashyap

Bhattacharjee

Arumugam

et al. 2021

JPM

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Background: In transcranial direct current stimulation (tDCS), the injected current becomes distributed across the brain areas. The objective is to stimulate the target region of interest (ROI) while minimizing the current in non-target ROIs (the ‘focality’ of tDCS). For this purpose, determining the appropriate current dose for an individual is difficult. Aim: To introduce a dose–target determination index (DTDI) to quantify the focality of tDCS and examine the dose–focality relationship in three different populations. Method: Here, we extended our previous toolbox i-SATA to the MNI reference space. After a tDCS montage is simulated for a current dose, the i-SATA(MNI) computes the average (over voxels) current density for every region in the brain. DTDI is the ratio of the average current density at the target ROI to the ROI with a maximum value (the peak region). Ideally, target ROI should be the peak region, so DTDI shall range from 0 to 1. The higher the value, the better the dose. We estimated the variation of DTDI within and across individuals using T1-weighted brain images of 45 males and females distributed equally across three age groups: (a) young adults (20 ≤ x ˂ 40 years), (b) mid adults (40 ≤ x ˂ 60 years), and (c) older adults (60 ≤ x ˂ 80 years). DTDI’s were evaluated for the frontal montage with electrodes at F3 and the right supraorbital for three current doses of 1 mA, 2 mA, and 3 mA, with the target ROI at the left middle frontal gyrus. Result: As the dose is incremented, DTDI may show (a) increase, (b) decrease, and (c) no change across the individuals depending on the relationship (nonlinear or linear) between the injected tDCS current and the distribution of current density in the target ROI. The nonlinearity is predominant in older adults with a decrease in focality. The decline is stronger in males. Higher current dose at older age can enhance the focality of stimulation. Conclusion: DTDI provides information on which tDCS current dose will optimize the focality of stimulation. The recommended DTDI dose should be prioritized based on the age (>40 years) and sex (especially for males) of an individual. The toolbox i-SATA(MNI) is freely available.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Focality-Oriented Selection of Current Dose for Transcranial Direct Current Stimulation

Kashyap

Bhattacharjee

Arumugam

et al. 2021

JPM

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“…This maximizes patient comfort and also eliminates risks from potential surgical interventions. Another advantage compared to electric stimulation is the relatively uniform distribution of magnetic permeability in the tissue, which makes it possible to control the magnetic field distribution precisely [18]. However, one large disadvantage comes from the fact that a considerably higher amount of energy is required for magnetic stimulation, therefore devices are large and expensive.…”

Section: Introductionmentioning

confidence: 99%

Coil Efficiency for Inductive Peripheral Nerve Stimulation

Braun

Rapp

Hemmert³

et al. 2022

IEEE Trans. Neural Syst. Rehabil. Eng.

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Magnetic stimulation of peripheral nerves is evoked by electric field gradients caused by high-intensity, pulsed magnetic fields created from a coil. Currents required for stimulation are very high, therefore devices are large, expensive, and often too complex for many applications like rehabilitation therapy. For repetitive stimulation, coil heating due to power loss poses a further limitation. The geometry of the magnetic coil determines field depth and focality, making it the most important factor that determines the current required for neuronal excitation. However, the comparison between different coil geometries is difficult and depends on the specific application. Especially the distance between nerve and coil plays a crucial role. In this investigation, the electric field distribution of 14 different coil geometries was calculated for a typical peripheral nerve stimulation with a 27 mm distance between axon and coil. Coil parameters like field strength and focality were determined with electromagnetic field simulations. In a second analysis, the activating function along the axon was calculated, which quantifies the efficiency of neuronal stimulation. Moreover, coil designs were evaluated concerning power efficacy based on ohmic losses. Our results indicate that power efficacy of magnetic neurostimulation can be improved significantly by up to 40 % with optimized coil designs.

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“…The age cut-off points of the present sample were kept same as in our previous study (Kashyap et al, 2021) to have a consistency in the findings. Although the threshold of DTDI at 0.75 was inspired from previous nerve stimulation studies that found this threshold to be optimal in stimulating the target region (Tigra et al, 2016;Kosta et al, 2019), additional analysis was performed here to determine the optimality of DTDI (please see methods section "Additional analysis of focality").…”

Section: Introductionmentioning

confidence: 99%

Variation of cerebrospinal fluid in specific regions regulates focality in transcranial direct current stimulation

Kashyap

Bhattacharjee

Bharath

et al. 2022

Front. Hum. Neurosci.

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BackgroundConventionally, transcranial direct current stimulation (tDCS) aims to focalize the current reaching the target region-of-interest (ROI). The focality can be quantified by the dose-target-determination-index (DTDI). Despite having a uniform tDCS setup, some individuals receive focal stimulation (high DTDI) while others show reduced focality (“non-focal”). The volume of cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM) underlying each ROI govern the tDCS current distribution inside the brain, thereby regulating focality.AimTo determine the regional volume parameters that differentiate the focal and non-focal groups.MethodsT1-weighted images of the brain from 300 age-sex matched adults were divided into three equal groups- (a) Young (20 ≤ × < 40 years), (b) Middle (40 ≤ × < 60 years), and (c) Older (60 ≤ × < 80 years). For each group, inter and intra-hemispheric montages with electrodes at (1) F3 and right supraorbital region (F3-RSO), and (2) CP5 and Cz (CP5-Cz) were simulated, targeting the left- Dorsolateral Prefrontal Cortex (DLPFC) and -Inferior Parietal Lobule (IPL), respectively. Both montages were simulated for two current doses (1 and 2 mA). For each individual head simulated for a tDCS configuration (montage and dose), the current density at each region-of-interest (ROI) and their DTDI were calculated. The individuals were categorized into two groups- (1) Focal (DTDI ≥ 0.75), and (2) Non-focal (DTDI < 0.75). The regional volume of CSF, GM, and WM of all the ROIs was determined. For each tDCS configuration and ROI, three 3-way analysis of variance was performed considering- (i) GM, (ii) WM, and (iii) CSF as the dependent variable (DV). The age group, sex, and focality group were the between-subject factors. For a given ROI, if any of the 3 DV’s showed a significant main effect or interaction involving the focality group, then that ROI was classified as a “focal ROI.”ResultsRegional CSF was the principal determinant of focality. For interhemispheric F3-RSO montage, interaction effect (p < 0.05) of age and focality was observed at Left Caudate Nucleus, with the focal group exhibiting higher CSF volume. The CSF volume of focal ROI correlated positively (r ∼ 0.16, p < 0.05) with the current density at the target ROI (DLPFC). For intrahemispheric CP5-Cz montage, a significant (p < 0.05) main effect was observed at the left pre- and post-central gyrus, with the focal group showing lower CSF volume. The CSF volume correlated negatively (r ∼ –0.16, p < 0.05) with current density at left IPL. The results were consistent for both current doses.ConclusionThe CSF channels the flow of tDCS current between electrodes with focal ROIs acting like reservoirs of current. The position of focal ROI in the channel determines the stimulation intensity at the target ROI. For focal stimulation in interhemispheric F3-RSO, the proximity of focal ROI reserves the current density at the target ROI (DLPFC). In contrast, for intrahemispheric montage (CP5-Cz), the far-end location of focal ROI reduces the current density at the target (IPL).

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Selective stimulation of rat sciatic nerve using an array of mm‐size magnetic coils: a simulation study

Cited by 9 publications

References 25 publications

Focality-Oriented Selection of Current Dose for Transcranial Direct Current Stimulation

Focality-Oriented Selection of Current Dose for Transcranial Direct Current Stimulation

Coil Efficiency for Inductive Peripheral Nerve Stimulation

Variation of cerebrospinal fluid in specific regions regulates focality in transcranial direct current stimulation

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