A real-time phase-dependent closed-loop neuromodulation system for direct cortical stimulation

Open-loop deep brain stimulation (DBS) has been used to treat multiple network-based neurological disorders. Reducing invasiveness of stimulation devices is one way to reduce the risk of surgical complications and unintended stimulation effects, and direct cortical stimulation is being explored for this reason. Phase-targeted motor cortex stimulation may be an effective paradigm for alleviating Parkinsonian motor symptoms and mesial temporal lobe phase-targeted stimulation is being explored for increases in performance during working memory tasks. As abnormal neural oscillation patterns associated with other disorders become known, there may be even more applications for timed stimulation therapies. Previous studies have shown that the implementation of this stimulation for more than a few milliseconds is challenging with the currently available hardware. Here, we present a method to perform accurate phase-targeted stimulation for longer periods of time on a low Size, Weight, and Power (SWAP) computation platform. This low SWAP platform consists of an FPGA and ARM processor on the same system on a chip (SoC). We evaluated our device's performance by measuring the average computation latency and the accuracy of peak targeting stimulation on a pure 20 Hz sine wave and intraoperative motor cortex beta-band (13-30 Hz) electrocorticography (ECoG) recordings. We found that our device was able to consistently trigger stimulation near the peak phases of an incoming signal for multiple seconds at a time. We believe that this device is an important step forward in developing a chronically implantable phase-targeted stimulation system.