The ability to reliably and chronically introduce electrical signals directly into the brain is crucial for a host of efforts to create neural prostheses as well as for basic research to understand brain function. Our goal is to further these efforts by developing a novel micro-coil based magnetic stimulation device suitable for implantation into cortex or into other regions of the CNS. Magnetic stimulation from micro-coils offers some important advantages over conventional electric stimulation. First, unlike the electric fields arising from implanted electrodes, the fields induced by coils are spatially asymmetric and can therefore be harnessed to create strong activating forces along a given orientation without creating strong activating forces in orthogonal directions. Thus, in the cortex for example, vertically-oriented pyramidal neurons can be strongly activated without simultaneously activating horizontally-oriented processes or the passing axons of distant neurons. Novel coil designs can be used to enhance selectivity even further and precisely control the volume of activation. A second important advantage of coils is that because magnetic fields pass readily through biological materials, the high impedance glial sheath that encapsulates cortical implants over time will not diminish the effectiveness of coils the way it can for electrodes. Finally, because there is no direct contact between the coil and neural tissue, electric current does not flow into the brain, making coils safer and less prone to many of the problems that occur at the interface between electrode and brain. Thus a coil-based prosthetic provides more precise activation of cortical targets than does electrodes and will remain stable over longer periods of time. The aims of this proposal are to further enhance the efficacy and selectivity of micro- coils by optimizing coil designs, developing stimulation strategies to effectively drive neuronal circuits, longitudinal testing to confirm performance metrics over time and finally, establishing efficacy in a nonhuman primate model.

Conventional electrode-based cortical implants offer tremendous potential to treat a wide range of neural diseases. Unfortunately, existing implants provide very limited control over which neurons become targeted by stimulation and are also plagued by a series of biological reactions that can `encapsulate' the device thereby greatly reducing its effectiveness over time. Here, we describe how tiny micro-coil-based implants can be used to magnetically activate neurons; this approach provides much greater selectivity of neuronal activation and also much less sensitivity to the biological reactions that impede the function of conventional electrodes.