Micro-TMS Technology for Ultra-Focal Brain Stimulation

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Abstract Micro-magnetic stimulation (μMS) is an emerging technology with a great promise to revolutionize therapeutic stimulation of human nervous system. Originally developed to stimulation single neurons, μMS uses ultra- conductive neuron-size coils that are capable of carrying current pulses large enough to elicit neural activation by means of magnetic induction. Depending on their dimension, μMS probes are capable of inducing neuronal activation in small areas limited to a few hundred microns to a few millimeters, rendering the technology a unique tool for ultra-focal brain stimulation. Our laboratory of Analogue Brain Imaging (ABILAB) at Massachusetts General Hospital is one of the frontrunners of advancing μMS research. We were the first group demonstrating the feasibility of using μMS probes implanted in deep brain structures to deliver therapeutic stimulation with effects analogous to the state-of-the-art deep brain stimulation. Joining forces with Berenson-Allen Center for Noninvasive Brain Stimulation at Beth Israel Deaconess Medical Center, we propose to adapt μMS technology to develop the first generation of miniaturized TMS (μTMS) elements for ultra-focal non-invasive brain stimulation. Taking advantage of the latest advancements in nano-fabrication, it is now possible to manufacture highly-conductive long traces with cross-sections as small as a few square microns. By carefully depositing hundreds of turns of such nano-structures in an annulus surface area less than a centimeter square, we will generate electric fields large enough to penetrate the skull and stimulate the cortex, yet not inducing discomfort at the skin level. Such advancement will have a transformative impact on the applicability of non-invasive brain stimulation, as it allows for a well-controlled stimulating and mapping of the human cortex with an unprecedented resolution. Moreover, because of their ultra-small size, μTMS elements can be integrated in multi-channel whole- head conformal arrays that will fit in a human head size helmet, enabling for the first time, the simultaneous multifocal stimulation of the human brain.