Deep transcranial magnetic stimulation for the addiction treatment: Electric field distribution modeling

Deep Transcranial Magnetic Stimulation (dTMS) is a neurostimulation technique for deep brain structures that has recently been successfully applied in the clinic for treatment of addiction. In contrast to conventional magnetic stimulation, which uses planar coils (figure-of-8) to target specific superficial regions of the brain, dTMS requires the design of complex three-dimensional coils in order to induce deeply penetrating fields. Recent clinical studies have focused on the use of H4 coils, which utilizes a left-right symmetric structure for bilateral stimulation of the prefrontal cortex, and demonstrated efficacy for therapy such as smoking cessation. The mechanism of activity, however, remains poorly understood, in part because the affected regions of the brain are not known in detail. To this purpose, computational techniques applied to highly detailed inhomogeneous tissue phantoms, provide a powerful tool for testing coil efficacy. In this work we quantified both electric field E distribution and its penetration depth in the prefrontal cortex, induced by a specific Hesed-coil, H4, designed for the addiction treatment and by the traditional figure-of-8 coil for comparison. Results show that H4 coil preferentially targets insula and cingulate cortex. Moreover, it can induce in the deepest tissues E amplitude ranging between the 20-40% of the cortical peak and it can penetrate the cortex up to 4 cm with a E>50% of the cortical peak, thus noticeably increasing the penetration depth of the traditional TMS systems.