Optimization of application of current

1. Apparatus, for use with a nerve of a subject, the apparatus comprising:

an implant, having a longitudinal axis, injectable into the subject along the longitudinal axis, and comprising:

an elongate housing having a first half including a first end, and a second half including a second end;

at least one paresthesia-inducing electrode disposed on a first site of the housing within the first half;

at least one blocking electrode disposed on a second site of the housing within the second half; and

circuitry, having:

a first mode in which the circuitry simultaneously drives (i) the at least one paresthesia-inducing electrode to apply a paresthesia-inducing current having a frequency of 2-400 Hz, and (ii) the at least one blocking electrode to apply a blocking current having a frequency of 1-20 kHz, and

a second mode in which the circuitry (i) drives the at least one blocking electrode to apply the blocking current, but (ii) does not drive the at least one paresthesia-inducing electrode to apply the paresthesia-inducing current,

wherein the circuitry is configured such that during at least 90 percent of the time that the blocking current is driven, the paresthesia-inducing current is not driven.

2. The apparatus according to claim 1 , wherein, while the circuitry is in the first mode, the circuitry drives the at least one blocking electrode to apply a blocking current having a frequency of 3-10 kHz.

3. The apparatus according to claim 1 , wherein the implant is dimensioned to be injectable into an epidural space of a subject.

4. The apparatus according to claim 1 , wherein:

the apparatus further comprises an extracorporeal controller, the extracorporeal controller:

comprising a battery and an extracorporeal antenna, and

configured to provide wireless power using the battery and the extracorporeal antenna; and

the implant further comprises an intracorporeal antenna, the intracorporeal antenna configured to:

receive the wireless power, and

provide the wireless power to the circuitry.

5. The apparatus according to claim 1 , wherein the circuitry has a third mode in which the circuitry drives the paresthesia-inducing electrode to apply the paresthesia-inducing current while not driving the blocking electrode to apply the blocking current.

6. The apparatus according to claim 5 , wherein the circuitry is configured such that during more than 30 percent of the time that the paresthesia-inducing current is driven, the blocking current is also driven.

7. The apparatus according to claim 1 , wherein:

the paresthesia-inducing electrode is configured to induce paresthesia by inducing action potentials in the nerve,

the blocking electrode is configured to block the induced action potentials from propagating along the nerve, and

the apparatus further comprises an implantable sensor unit, the sensor unit configured to detect induced action potentials in the nerve, and to responsively provide a sensor signal that conveys information about the detected induced action potentials, and wherein the circuitry is configured to receive the sensor signal, and to alter a parameter of the blocking current in response to the received sensor signal.

8. The apparatus according to claim 7 , wherein the blocking electrode is disposed between the paresthesia-inducing electrode and the sensor unit.

9. The apparatus according to claim 7 , wherein the implant is configured to be implanted at the nerve such that the sensor unit is disposed at a first nerve site, and the blocking electrode is disposed at a second nerve site that is efferent to the first nerve site.