Apparatus is provided including an assembly (22) and a control unit (36). The assembly (22) includes a housing (34) configured to be applied to a nerve (20) of a subject, and at least one cathode (30) and at least one Peltier cooler (32), which are fixed to the housing (34). The control unit (36) is configured to drive the cathode (30) to apply an activating current to the nerve (20) that generates action potentials traveling in first and second directions (38 and 40) in the nerve (20), and the Peltier cooler (32) to cool the nerve (20) sufficiently to block propagation of at least a portion of the cathode-generated action potentials traveling in the second direction (40). Other embodiments are also described.