Techniques for nerve stimulation

1. Apparatus for applying current to a nerve, comprising:

a control unit;

a housing, adapted to be placed in a vicinity of the nerve;

at least one cathode and at least one anode, fixed to the housing, and electrically device-coupled to the control unit;

two or more passive electrodes, fixed to the housing; and

a conducting element, which electrically couples the passive electrodes to one another,

wherein the control unit and passive electrodes are configured such that each of the passive electrodes is electrically device-coupled to neither (a) any circuitry that is electrically device-coupled to the at least one cathode or the at least one anode, nor (b) an energy source.

2. The apparatus according to claim 1 , wherein the two or more passive electrodes comprise exactly two passive electrodes.

3. The apparatus according to claim 1 , wherein the at least one cathode and the at least one anode are fixed longitudinally between the two or more passive electrodes.

4. The apparatus according to claim 1 , wherein at least one of the passive electrodes is fixed longitudinally between the at least one cathode and the at least one anode.

5. The apparatus according to claim 1 , wherein the at least one anode comprises one or more anodes which are configured to apply to the nerve an inhibiting current capable of inhibiting cathode-induced action potentials traveling in a non-therapeutic direction in the nerve.

6. The apparatus according to claim 1 , wherein the at least one cathode comprises one or more cathodes which are configured to apply to the nerve a stimulating current, which is capable of inducing action potentials in a first set and a second set of nerve fibers of the nerve, and wherein the at least one anode comprises one or more anodes that are configured to apply to the nerve an inhibiting current, which is capable of inhibiting the induced action potentials in the second set of nerve fibers, the nerve fibers in the second set having generally larger diameters than the nerve fibers in the first set.

7. The apparatus according to claim 1 , wherein the electrodes comprise ring electrodes.

8. The apparatus according to claim 1 , wherein the conducting element comprises at least one passive element that impedes passage of current through the conducting element, the passive element selected from the group consisting of: a resistor, a capacitor, and an inductor.

9. The apparatus according to claim 1 , wherein the housing comprises one or more insulating elements that separate one or more of the at least one cathode, the at least one anode, and the passive electrodes, the insulating elements positioned closer to the nerve than are the at least one cathode, the at least one anode, and the passive electrodes.