Directional DBS and current steering

Directional DBS leads split one or more of the cylindrical ring contacts into radial segments (commonly three per level), so that current can be steered toward the therapeutic target and away from adjacent structures whose recruitment causes side effects. By reshaping the field asymmetrically, current steering can widen the therapeutic window compared with a symmetric ring, especially when the lead sits slightly off the ideal trajectory.

Steering is realized by fractionating current across segments and levels, best done with multiple independent current sources so segment currents are set independently. The costs are a much larger programming parameter space (a driver for imaging-guided, model-guided, and increasingly automated programming to keep the search tractable) and the requirement that the lead's rotational orientation be known, usually recovered from postoperative imaging, since steering in the wrong azimuth is worse than a plain ring.