Where does transcranial magnetic stimulation (TMS) stimulate? Modelling of induced field maps for some common cortical and cerebellar targets

Abstract

Computational models have been be used to estimate the electric and magnetic fields induced by transcranial magnetic stimulation (TMS) and can provide valuable insights into the location and spatial distribution of TMS stimulation. However, there has been little translation of these findings into practical TMS research. This study uses the International 10-20 EEG electrode placement system to position a standard figure-of-eight TMS coil over 13 commonly adopted targets. Using a finite element method and an anatomically detailed and realistic head model, this study provides the first pictorial and numerical atlas of TMS-induced electric fields for a range of coil positions. The results highlight the importance of subject-specific gyral folding patterns and of local thickness of subarachnoid cerebrospinal fluid (CSF). Our modelling shows that high electric fields occur primarily on the peaks of those gyri which have only a thin layer of CSF above them. These findings have important implications for inter-individual generalizability of the TMS-induced electric field. We propose that, in order to determine with accuracy the site of stimulation for an individual subject, it is necessary to solve the electric field distribution using subject-specific anatomy obtained from a high-resolution imaging modality such as MRI.

Cranial electrotherapy stimulation and transcranial pulsed current stimulation: A computer based high-resolution modeling study

“…The peak electric field magnitudes generated during CES (b1 V/m) are approximately 100-1000 fold lower than electric fields induced by transcranial magnetic stimulation (TMS) or electroconvulsive therapy (ECT) (Bijsterbosch et al, 2012;De Geeter et al, 2012;Deng et al, in press;. This finding is expected as these later approaches (TMS and ECT) lead to supra-threshold neuronal firing.…”

Pediatric stroke and transcranial direct current stimulation: methods for rational individualized dose optimization

“…The models assume that the damaged brain regions have similar conductivity of cerebral spinal fluid while the peri-lesional area has the conductivity of healthy brain (Bijsterbosch et al, 2012). However, increased precision could incorporate changes in conductivity considering resultant gliosis or other pathologic processes that accompany cerebral lesions (Ruohonen and Karhu, 2012; Huang et al, 2014).…”

Nonlinear effects of respiration on the crosstalk between cardiovascular and cerebrovascular control systems

“…Recent studies have even attempted to model the impact of cortical gyration at the individual level [114], with results suggesting the field strength as being significantly enhanced when the currents run approximately perpendicular to the local gyral orientation [115,116]. This evidence, implying an even more careful selection of coil orientation in order to realistically target given cortical areas, has been recently expanded by studies focusing on the role of tissue anisotropy (using diffusion tensor (DTI) and diffusion-weighted (DWI) imaging) to determine the probability to target specific white matter tracts [115,117], thus directly perturbing the structural 'connectome'.…”