Apparatus is configured to drive first action potentials orthodromically in a first direction along a nerve of a subject, and second action potentials orthodromically along the nerve in an opposite direction to the first direction. The apparatus includes: (1) first and second excitation units configured to be placed in a proximity of the nerve of the subject； (2) a blocking unit disposed between the excitation units and placeable in a proximity of the nerve of the subject； and (3) a control unit, configured: (i) to drive the first and second excitation units to apply, respectively, first and second excitatory currents to the nerve of the subject, and (ii) to drive the blocking unit to apply a blocking current to the nerve of the subject that blocks action potentials that propagate from the first and second excitatory units toward the blocking unit. Other embodiments are also described.
