Electric-field-based TMS-dosing
Poster No:
125
Submission Type:
Abstract Submission
Authors:
Ole Numssen1, Philipp Kuhnke2, Konstantin Weise1,3, Gesa Hartwigsen2
Institutions:
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, 2Leipzig University, Leipzig, Saxony, 3Leipzig University of Applied Sciences, Leipzig, Germany
First Author:
Co-Author(s):
Konstantin Weise
Max Planck Institute for Human Cognitive and Brain Sciences|Leipzig University of Applied Sciences
Leipzig, Saxony|Leipzig, Germany
Max Planck Institute for Human Cognitive and Brain Sciences|Leipzig University of Applied Sciences
Leipzig, Saxony|Leipzig, Germany
Introduction:
Non-invasive brain stimulation (NIBS), notably transcranial magnetic stimulation (TMS), has transformed our understanding of brain function and its modulation in health and disease. However, challenges persist, particularly in achieving consistent and reliable outcomes due to high variability in individual responses. One crucial factor influencing the variability of NIBS effects is the stimulation intensity or "dosing". The gold standard for dosing, the motor threshold (MT), faces limitations in accurately calibrating cortical stimulation exposure across diverse brain regions. Here [1], we present an electric field (e-field) based dosing approach, providing a promising avenue to overcome these limitations. This approach utilizes individualized simulations of NIBS-induced e-fields to precisely match cortical stimulation exposure within and across individuals, offering potential improvements in the reliability and efficacy of NIBS.
Methods:
Based on high-resolution head models [2] constructed from structural MRI images, we computed the TMS-induced e-fields for several stimulation sites for 18 healthy subjects. By using our previously proposed TMS-mapping procedure [3], we precisely identified finger muscle representations in the primary motor cortex. After measuring the resting motor threshold (rMT) in an experimental session, we calculated the cortical stimulation intensity (|E| in V/m) in the primary motor cortex at rMT to quantify the cortical excitation threshold on an individual and bio-physiologically plausible level. Subsequently, we compared the realized cortical stimulation intensity at four cortical regions (somatomotor cortex, auditory cortex, inferior parietal lobe, dorsolateral prefrontal cortex) in each subject for three different TMS dosing approaches: rMT-based dosing, Stokes-adjusted [4], and e-field based dosing. Specifically, we compared the realized stimulation intensities at these four targets for all three dosing approaches with the individual, cortical excitability threshold quantified in M1.
Results:
In comparison to MT-based and Stokes-adjusted dosing, e-field dosing optimally matches the cortical stimulation strength both within (Fig. 1) and across individuals (Fig. 2). Interestingly, the Stokes adjustment does not better match the cortical stimulation strength between targets than simple MT-based dosing. E-field based dosing minimizes the within-subject variance of cortical stimulation exposure, as each cortical target receives the same stimulation strength, addressing a longstanding challenge in NIBS research. Across subjects, the cortical excitation threshold is determined at ~60 V/m, with substantial differences between individuals ranging from ~40 V/m to ~90 V/m, potentially identifying imperfections in the modeling pipeline (such as differences in tissue conductivities). On average, however, e-field dosing matches the cortical stimulation strength between targets also across participants.
Conclusions:
In conclusion, e-field based dosing represents a promising advancement in the field of non-invasive brain stimulation, both for neuroscientific research and clinical applications. By moving beyond the limitations of MT-based (and Stokes-adjusted) dosing, this approach offers a robust and individualized strategy for calibrating cortical stimulation exposure. By better standardizing the cortical stimulation exposure across subjects and within subjects across brain regions, we aim to decrease the variance of NIBS effects that often impede strong group-level effects.
Brain Stimulation:
Non-invasive Magnetic/TMS
TMS 1
Modeling and Analysis Methods:
Methods Development 2
Neuroinformatics and Data Sharing:
Workflows
Keywords:
Other - dosing; standardization; dosimetry; stokes; TMS, e-field; FEM
1|2Indicates the priority used for review
Provide references using author date format
2. Puonti, O., Van Leemput, K., Saturnino, G. B., Siebner, H. R., Madsen, K. H., & Thielscher, A. (2020). Accurate and robust whole-head segmentation from magnetic resonance images for individualized head modeling. Neuroimage, 219, 117044.
3. Numssen O, Zier AL, Thielscher A, Hartwigsen G, Knösche TR, Weise K. Efficient high-resolution TMS mapping of the human motor cortex by nonlinear regression. Neuroimage. 2021 Dec 15;245:118654. doi: 10.1016/j.neuroimage.2021.118654. Epub 2021 Oct 12. PMID: 34653612.
4. Stokes, M. G., Chambers, C. D., Gould, I. C., Henderson, T. R., Janko, N. E., Allen, N. B., & Mattingley, J. B. (2005). Simple Metric For Scaling Motor Threshold Based on Scalp-Cortex Distance: Application to Studies Using Transcranial Magnetic Stimulation. J. Neurophysiol., 94, 4520–4527. DOI: 10.1152/jn.00067.2005