Computation of in situ electric field in the brain during transcranial magnetic stimulation

The study of magnetic stimulation of the human brain has been an on-going research topic since the 1980s. To achieve a better understanding of the cerebral stimulation, it is necessary to estimate the spatial distribution and peak magnitude of the induced electric field in the brain. By utilizing a high resolution anatomical model and a numerical technique based on quasi-static approximation, this study provides a state-of-the-art estimation of the in situ electric field distribution in an adult brain when undergoing transcranial magnetic stimulation. Coil designs such as figure-8 and 4-leaf-clover are employed in the analysis. It is demonstrated that the brain regions which are more likely to be stimulated by the respective coil design can be better estimated by employing a realistic anatomical model than a homogeneous model. It is revealed that the location of the maximum in situ electric field does not necessarily coincide with the location of the maximum magnetic flux (directly below the coil). Instead, the site of stimulation is significantly influenced by the design of the coil and the coil position.