Therapeutic window (stimulation)

The therapeutic window is the range of stimulation intensity between the threshold at which clinical benefit appears and the threshold at which intolerable side effects begin. In subthalamic DBS, for example, benefit thresholds compete with side effects from current spreading to neighbouring structures: capsular motor contractions and dysarthria from the internal capsule and corticobulbar fibers, and mood or impulsivity changes from limbic and associative territory. A wide window means the target can be stimulated therapeutically with comfortable margin; a narrow one leaves little room.

A narrow window usually reflects the anatomical proximity of the target to off-target structures rather than a limitation of the device itself. Consequently, widening the window is a central engineering goal, pursued through more accurate lead placement, directional current steering, novel waveforms and pulse shapes, and closed-loop dosing that supplies only the stimulation the moment requires. Reporting the therapeutic window, not just an efficacy threshold, is important because two settings with equal benefit can differ greatly in safety margin.