Prof. Dick Stegeman

Radboud university Medical center

Dick F. Stegeman received a MSc degree in electrical engineering in 1976 from the  University of Twente-NL. In 1981 he received a PhD degree at the Radboud University Nijmegen-NL. Presently he works as a medical physicist at the RadboudUMC, Department of Neurology. Since 2003, he is also full professor of applied electrophysiology at the Faculty of Human Movement Sciences at the VU University, Amsterdam. His interests concern electrophysiological modeling and the measurement and quantitative analysis of electroneurographic, EMG and EEG data. The present research concentrates on spatio-temporal information in electrophysiological data and the use and modeling of non-invasive brain stimulation (TMS, tDCS) for diagnosis and therapy.

Finite element model based prediction of electric fields in the human brain after TMS and tDCS stimulation

Transcranial magnetic stimulation (TMS) and transcranial (direct) current stimulation (tDCS) are techniques that can induce changes in cortical excitability of the stimulated brain areas. These techniques are non-invasive and easy to apply. The mechanisms are still largely unknown. To gain insight into mechanisms, one of the first things to quantify is the electric field in the brain induced by TMS and tDCS . This can be done with the use of computational model simulations. A highly realistic head model was constructed using three-dimensional boundaries of eight different tissue types (skin, skull spongiosa, skull compacta, neck muscle, eye, CSF, GM and WM), which were based on T1 and T2 magnetic resonance images (MRI) scans of a healthy 25-year old male subject with 1mm3 resolution. Anisotropy of these structures is taken into account using DTI recordings. The model contains several millions of tetrahedral elements. With this model, electric fields induced by TMS or tDCS can accurately be predicted.
Several questions have been posed to this model, e.g.:
– Which detail with respect to the tissue anatomy and properties is necessary to get appropriate predictions from the model?
– What is the influence of the position and the orientation of the TMS coil over the skull?
– Are the tDCS electrode locations used as standards in the literature optimal and , if not, what are the optimal locations?
– Which is expected to be the most probably electric field direction to induce changes?