Fig 1. Six different configurations of the 12 contacts electrode were tested: Ring, tripolar transverse ring (TTR), tripolar transverse (TT), tripolar longitudinal ring (TLR), tripolar longitudinal (TL) and steering current ring (SCR).

Each configuration is composed of a unique active site (cathode) on the central ring B (red) and several return path (anode, blue) for which the current ratio is imposed [9]. Only one electrode conformation is presented here (cathode position). The row A is proximal to the spinal cord whereas the row C is distal.