Computational estimate of the induced electric field along neuronal fibers in TMS applications

The navigated Transcranial Magnetic Stimulation (nTMS) has recently proved to be a valid and promising tool both for the therapeutic treatment of a wide range of neurological and psychiatric disorders [1] , both for pre-surgical planning in patients with brain tumor lesions [2]. In both cases, it is of crucial importance the knowledge of the electric field (E) distribution induced in the brain regions of interest by a coil placed near the scalp. Generally, stimulation is considered effective if the intensity of E exceeds a certain threshold, of the order of 80-100 V/m. Recent studies have shown that the effectiveness of a TMS application significantly depends on the coupling of the E field in the direction of the neuronal fibers [3] as well as on the local intensity. Aim of this work is to provide a tool, based on the rigorous calculation of the E field along neuronal fibers, that provides the best coil positioning able to induce the stimulation of the region of interest.