Custom TMS coils designs for single and multi-locus stimulation of the cerebellum
Víctor Salas Moreno1, Jose Antonio Vilchez Membrilla1, Roman Shalamov2
1Department of Electronics, University of Cadiz, Cadiz, Spain.
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Objective.Despite the growing interest in cerebellar transcranial magnetic stimulation (TMS), dedicated coil designs for cerebellar targeting remain limited. This work introduces a systematic framework for the design of TMS coils specifically tailored for cerebellar stimulation. The aim of this study is to achieve flexible and accurate targeting of cerebellar regions while minimising unintended effects of adjacent cortical structures.Approach.Coil geometries were adapted to anatomically realistic head models derived from magnetic resonance imaging data of eight subjects. An inverse boundary element method was combined with a multi-objective optimisation problem (MOP) framework to explicitly control the focality and penetration depth of the induced electric field, yielding up to 100 candidate optimal coil designs. Two curved geometries were optimised for single-site and multi-locus stimulation using a combination of three coils. The characteristics of the resulting coils were evaluated by computing the electric field on spherical and anatomically realistic head models implemented in SimNIBS 4.5.Main results.The optimised designs demonstrated improved trade-off between focality and depth compared with conventional figure-of-eight and double-cone coils. When assessed in realistic head models, both geometries achieved higher spatial specificity within the cerebellum, inducing approximately 24% more volume of the region of interest and 66% less in the non-target region. Furthermore, with the proposed MOP framework, we identified a three-coil configuration capable of electronically steering stimulation within a 20 mm cerebellar region.Significance.The proposed approach enables anatomically adapted coil design with explicit field control, enhancing the precision and efficiency of cerebellar TMS. This framework establishes a robust basis for creating custom TMS coils with improved performance on future experimental and therapeutic applications involving the cerebellum.
