EM fields comparison between planar vs. solenoidal μMS coil designs for nerve stimulation

Micro-magnetic stimulation (μMS) is an emerging neurostimulation technology that promises to revolutionize the therapeutic stimulation of the human nervous system. μMS uses sub-millimeter sized coils that can be implemented in the central nervous system to elicit neuronal activation using magnetically induced electric currents. By their microscopic size, μMS coils can be acutely implanted in deep brain structures to deliver therapeutic stimulation with effects analogous to those achieved by state-of-the-art deep brain stimulation (DBS). However, μMS technology has inherent advantages that make it particularly appealing for clinical applications. Specifically, μMS induces a focal electric current in the tissue, limiting the extent of activation to a few hundred microns. We recently demonstrated the feasibility of using μMS to elicit neuronal activation in vitro [1], as well as the possibility of activating neuronal circuitry on the system level in rodents [2]. As μMS is a novel technology, its mechanism(s) of nerve activation, induced field characteristics, and optimum topological features are yet to be explored. In this regard, numerical simulations play a crucially important role, because they provide an insight into spatial distribution of induced electric fields, which in turn, dictate the dynamics of nerve stimulation. Here we report results of numerical simulations to predict the nerve-stimulation performance of different μMS geometries.