Targeting of white matter tracts with transcranial magnetic stimulation

Aapo Nummenmaa, Jennifer A. McNab, Peter Savadjiev, Yoshio Okada, Matti S. Hämäläinen, Ruopeng Wang, Lawrence L. Wald, Alvaro Pascual-Leone, Van J. Wedeen, Tommi Raij*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Background TMS activations of white matter depend not only on the distance from the coil, but also on the orientation of the axons relative to the TMS-induced electric field, and especially on axonal bends that create strong local field gradient maxima. Therefore, tractography contains potentially useful information for TMS targeting. Objective/methods Here, we utilized 1-mm resolution diffusion and structural T1-weighted MRI to construct large-scale tractography models, and localized TMS white matter activations in motor cortex using electromagnetic forward modeling in a boundary element model (BEM). Results As expected, in sulcal walls, pyramidal cell axonal bends created preferred sites of activation that were not found in gyral crowns. The model agreed with the well-known coil orientation sensitivity of motor cortex, and also suggested unexpected activation distributions emerging from the E-field and tract configurations. We further propose a novel method for computing the optimal coil location and orientation to maximally stimulate a pre-determined axonal bundle. Conclusions Diffusion MRI tractography with electromagnetic modeling may improve spatial specificity and efficacy of TMS.

Original languageEnglish (US)
Pages (from-to)80-84
Number of pages5
JournalBrain Stimulation
Issue number1
StatePublished - Jan 2014


  • Coil orientation
  • Diffusion MRI tractography
  • Electromagnetic modeling
  • Navigation
  • TMS
  • Transcranial magnetic stimulation

ASJC Scopus subject areas

  • Biophysics
  • Neuroscience(all)
  • Clinical Neurology


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