Accurate brain stimulation requires precise neuroanatomical information. To activate a specific brain region with transcranial magnetic stimulation (TMS), it is important to know where on the scalp to place the induction coil. Commercial neuronavigation systems have been developed for this purpose. However, it is also important to know the depth of the targeted area, because the effect of TMS critically depends on the distance between the stimulating coil and targeted brain area.
We have developed a simple TMS Distance Toolbox for calculating the distance between a stimulation site on the scalp surface and underlying cortical surface. The toolbox can be download here, and requires Matlab and SPM8. I will posted further information soon, including user instructions.