Apparatus and methods for stimulating tissue

A neurostimulation system, comprising:

• an implantable lead, having a plurality of lead electrodes, adapted to be disposed in a target tissue region having target tissue and non-target tissue such that the non-target tissue is disposed between the plurality of lead electrodes and the target tissue, the target tissue region having a first neural fiber bundle and a second neural fiber bundle, the target tissue comprising the second neural fiber bundle;
• a remote electrode adapted to be disposed in a remote location such that stimulation current sourced from or sunk at the remote electrode does not produce a therapeutic effect in the target tissue region;
• an implanted pulse generator (IPG) operably connected to the plurality of lead electrodes, the IPG comprising an IPG case configured to function as an electrode (“case electrode”) and a control circuit configured to:
• source a first anodic portion of a current at a first lead electrode of the plurality of lead electrodes;
• source a second anodic portion of the current at a second lead electrode of the plurality of lead electrodes;
• sink a first cathodic portion of the sourced current at a third lead electrode of the plurality of lead electrodes, wherein the first cathodic portion of the sourced current has a magnitude sufficient to generate action potentials in neural fibers in the first and second neural fiber bundles, the first neural fiber bundle being a first distance from the implantable lead and the second neural fiber bundle being a second distance, that is different than the first distance, from the implantable lead, and wherein sinking the first portion of the current creates a local current imbalance in the target tissue region;
• and
• sink a second cathodic portion of the sourced current at the case electrode, wherein an overall current balance is maintained among the first lead electrode, the second lead electrode, the third lead electrode and the case electrode.

A method of using an implantable pulse generator (IPG) for neurostimulation, the IPG comprising an IPG case configured to function as an electrode (“case electrode”), the method comprising:

• selecting a first electrode in a target tissue region having target tissue and non-target tissue such that the non-target tissue is disposed between the plurality of lead electrodes and the target tissue, the first electrode configured to source a first anodic portion of a stimulation current;
• selecting a second electrode in the target tissue region, the second electrode configured to source a second anodic portion of the stimulation current;
• selecting a third electrode in the target tissue region, the third electrode configured for sinking a first cathodic portion of the stimulation current;
• selecting the case electrode, the case electrode configured for sinking a second cathodic portion of the stimulation current to reduce the amount of current sunk at the third electrode;
• sourcing the current at the first and second electrodes;
• sinking a first portion of the sourced current at the third electrode, wherein sinking the first portion of the current creates a local current imbalance in the target tissue region;
• and
• sinking a second portion of the sourced current at the case electrode to reduce the amount of current sunk at the third electrode and maintain an overall current balance among the first electrode, the second electrode, the third electrode, and the case electrode.