Apparatus is provided, comprising: (a) an implantable excitation unit (22), configured to induce action potentials in a nerve of a subject by applying an excitatory current； (b) an implantable blocking unit (24), configured to block the induced action potentials from propagating along the nerve by applying a blocking current； and (c) an extracorporeal controller (48), comprising circuitry (50) configured: (i) to wirelessly drive the excitation unit to apply the excitatory current, (ii) in a first mode, to wirelessly drive the blocking unit to apply the blocking current while not driving the excitation unit to apply the excitatory current, (iii) in a second mode, to wirelessly drive the blocking unit to apply the blocking current while driving the excitation unit to apply the excitatory current, and (iv) to wirelessly alter a parameter of the blocking current, based on sensing performed while the extracorporeal controller is in the second mode.
