Four electric field modeling methods of Dosing Prefrontal Transcranial Magnetic Stimulation (TMS): Introducing APEX MT dosimetry

We recently performed electric field (E-field) modeling on 38 structural magnetic resonance imaging (MRI) scans in the motor and prefrontal cortices to reexamine the widely used 120% resting motor threshold (rMT) dosing technique(1). Using the finite element method (FEM) to simulate electromagnetic currents passing through tissues with different conductivities (i.e. skin, bone, cerebrospinal fluid, grey matter, and white matter) [2], we found that TMS would need to be applied at an average of 133.5% of resting motor threshold (rMT) over the left prefrontal cortex to produce equivalent E-fields as 100% rMT stimulation over the left primary motor cortex, with large interindividual variability (range = 79.9–247.5% rMT) [1].