Efficient high-resolution TMS mapping of the human motor cortex by nonlinear regression

Ole Numssen*, Anna Leah Zier, Axel Thielscher, Gesa Hartwigsen, Thomas R. Knösche, Konstantin Weise

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Transcranial magnetic stimulation (TMS) is a powerful tool to investigate causal structure-function relationships in the human brain. However, a precise delineation of the effectively stimulated neuronal populations is notoriously impeded by the widespread and complex distribution of the induced electric field. Here, we propose a method that allows rapid and feasible cortical localization at the individual subject level. The functional relationship between electric field and behavioral effect is quantified by combining experimental data with numerically modeled fields to identify the cortical origin of the modulated effect. Motor evoked potentials (MEPs) from three finger muscles were recorded for a set of random stimulations around the primary motor area. All induced electric fields were nonlinearly regressed against the elicited MEPs to identify their cortical origin. We could distinguish cortical muscle representation with high spatial resolution and localized them primarily on the crowns and rims of the precentral gyrus. A post-hoc analysis revealed exponential convergence of the method with the number of stimulations, yielding a minimum of about 180 random stimulations to obtain stable results. Establishing a functional link between the modulated effect and the underlying mode of action, the induced electric field, is a fundamental step to fully exploit the potential of TMS. In contrast to previous approaches, the presented protocol is particularly easy to implement, fast to apply, and very robust due to the random coil positioning and therefore is suitable for practical and clinical applications.

Original languageEnglish
Article number118654
Number of pages11
Publication statusPublished - 2021


  • Brain mapping
  • Finite element analysis
  • Motor cortex
  • Motor threshold
  • Transcranial magnetic stimulation


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