Pointing in the right direction: Motor improvements with directional versus circular DBS

Directional brain stimulation provides greater control of radial current spread than conventional ring-shaped electrodes. Whether this added flexibility can improve motor function is unclear. Here we examine whether directional and circular stimulation differentially change motor performance in patients with Parkinsons disease. We measured motor behaviors in 31 patients who underwent unilateral subthalamic nucleus brain stimulation surgery (SUNDIAL, NCT03353688) from each of 8 configurations (6 directional contacts and their corresponding rings) during device activation. Objective measures of dexterity, gait, balance, and overall mobility were queried in a double-blind fashion in the practically defined "off" medication state versus preoperative baseline with stimulus amplitude at the center of the therapeutic window. The best versus the worst directional contact on a given row yields significant changes in performance across 5 motor tasks (p<0.001 each task). Specific stimulation directions can worsen function versus baseline, whereas the best direction yields greater improvement than ring stimulation (p=0.005, p=0.001, p=0.007, p<0.001, respectively, across tasks). Although directional DBS improves side effect thresholds versus ring stimulation (p<0.001), the side effect threshold and therapeutic window correlate only modestly with motor improvements. Resting beta power did not predict motor improvements by directional DBS across any of the motor tasks. Optimized directional subthalamic nucleus DBS yields better group-level motor performance than ring stimulation, in addition to known advantages related to tolerability. Prospective studies should evaluate whether these improvements persist over longer time intervals.