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. 2021 Jul-Aug;14(4):1032-1034.
doi: 10.1016/j.brs.2021.06.012. Epub 2021 Jun 26.

Four electric field modeling methods of Dosing Prefrontal Transcranial Magnetic Stimulation (TMS): Introducing APEX MT dosimetry

Kevin A Caulfield  1 , Xingbao Li  2 , Mark S George  3
Affiliations

Four electric field modeling methods of Dosing Prefrontal Transcranial Magnetic Stimulation (TMS): Introducing APEX MT dosimetry

Kevin A Caulfield et al. Brain Stimul. 2021 Jul-Aug.
No abstract available

Keywords: Dosing; Electric field modeling; Finite element method; Motor threshold; Prefrontal; Transcranial magnetic stimulation (TMS).

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Conflict of interest statement

Declaration of competing interest We confirm that there are no known conflicts of interest associated with this publication and there was no financial support for this work that could have influenced its outcome.

Figures

Figure 1:
Figure 1:. Four Methods of Dosing Prefrontal Transcranial Magnetic Stimulation (TMS) Using E-field Modeling.
In this figure, we show four methods of dosing prefrontal TMS using E-field modeling. 1A: Method 1: Application of 133.5% rMT. Method 1 applies a set 133.5% rMT stimulation intensity for each participant over the prefrontal cortex. This approach was informed by E-field modeling and our prior finding that an average of 133.5% rMT stimulation over the prefrontal cortex would need to be applied to produce equivalent E-fields as 100% rMT stimulation over the motor cortex. However, by simply updating the 120% rMT dosing adjustment between the motor and prefrontal cortices, there was still a 20.6% deviation (SD = 17.5%) between E-fields produced from the 133.5% rMT prefrontal dose and 100% rMT motor dose. 1B: Method 2: Regression of rMT x Prefrontal E-Field. Method 2 entails acquiring a rMT and plugging it into the regression formula for our previous data in Equation 1. This approach reduces the variation between the actual E-field from the prefrontal dose and predicted E-field from the prefrontal dose (regression line), with an average deviation of 16.9% (SD = 13.2%). 1C: Method 3: Prefrontal Group Average E-Field. Method 3 represents the most commonly utilized E-field dosing approach. The researcher applies prefrontal stimulation at an E-field intensity presumed to activate neuronal tissue, and this stimulation intensity is kept constant across every participant. Here we demonstrate the individual E-field differences between motor stimulation at 100% rMT and prefrontal stimulation at the group average of 158.2V/m (region of interest analysis at the cortical DLPFC target with a 10mm spherical radius and grey matter mask). However, this method is prone to under or over-dosing and is highly contingent on the chosen E-field threshold, which may differ between individuals based on age, population, or other factors. 1D: Method 4 (APEX MT): Combination of rMT and E-Field Modeling. We propose APEX MT as a new prefrontal dosing approach that combines the benefits of the rMT and E-field modeling. First, the researcher acquires a rMT for each person and performs motor E-field modeling to determine the individualized motor threshold E-field that produces neuronal firing (observed in the contralateral hand). Next, the researcher performs prefrontal E-field modeling at a set stimulation intensity to determine the input-output function based on the prefrontal tissue composition. Lastly, the researcher inputs these values into Equation 2 to determine the personalized prefrontal TMS intensity to produce motor-equivalent E-fields. APEX MT’s combined rMT x E-field modeling method ensures that there is 0% deviation between the motor E-fields at 100% rMT and E-fields from individualized prefrontal dosing. See the Supplementary Table for highlighted pros and cons of each approach.
See this image and copyright information in PMC

References

    1. Caulfield KA, Li X, George MS. A reexamination of motor and prefrontal TMS in tobacco use disorder: Time for personalized dosing based on electric field modeling? Clin Neurophysiol. 2021. Sep;132(9):2199–2207. doi: 10.1016/j.clinph.2021.06.015. Epub 2021 Jul 10. - DOI - PMC - PubMed
    1. Saturnino GB, Puonti O, Nielsen JD, Antonenko D, Madsen KH, Thielscher A. SimNIBS 2.1: A Comprehensive Pipeline for Individualized Electric Field Modelling for Transcranial Brain Stimulation. In: Makarov S, Horner M, Noetscher G, editors. Brain and Hum Bod Model 2018. Cham (CH): Springer; Copyright 2019, The Author(s). 2019. p. 3–25. - PubMed
    1. Caulfield KA, Badran BW, DeVries WH, Summers PM, Kofmehl E, Li X, et al. Transcranial Electrical Stimulation Motor Threshold Can Estimate Individualized tDCS Dosage from Reverse-Calculation Electric-Field Modeling. Brain Stimul. 2020;13(4):961–9. - PMC - PubMed
    1. Caulfield KA, Badran BW, Li X, Bikson M, George MS. Can Transcranial Electrical Stimulation Motor Threshold Estimate Individualized tDCS Doses Over the Prefrontal Cortex? Evidence from Reverse-Calculation Electric Field Modeling. Brain Stimul. 2020;13(4):1150–2. - PMC - PubMed
    1. Caulfield KA, Indahlastari A, Nissim NR, Lopez JW, Fleischmann HH, Woods AJ, et al. Electric Field Strength From Prefrontal Transcranial Direct Current Stimulation Determines Degree of Working Memory Response: A Potential Application of Reverse-Calculation Modeling? Neuromodulation : journal of the International Neuromodulation Society. 2020. - PubMed

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