Fig. 1. Overview of various types and generations of neurostimulation electrodes and microelectrode arrays.

Examples of older generations of percutaneous and paddle electrode arrays that included a four electrodes used in spinal cord stimulation devices. b Examples of newer generations of percutaneous arrays that include 8–16 electrodes and paddle arrays that include 16–32 electrodes to help improve stimulation selectivity and flexibility in spinal cord stimulation devices [a, b Photo reproduced with permission from Lempka, S⁹³]; c–e examples of commercial spinal cord stimulation devices for treatment of chronic pain: c Omnia™ System, and d Senza™ System by Nevro Corp. [c, d photos used with permission and courtesy of Nevro Corp.]; the Omnia™ System represents a percutaneous style of electrode (Pt10Ir alloy) array with 16 percutaneous (cylindrical) electrodes that is implanted in the spinal cord system. The Senza™ System represents a paddle style of electrode (Pt10Ir alloy) array with 16 flat electrodes that is implanted in the spinal cord system; e a spinal cord stimulator system with a percutaneous electrode array that includes 32 cylindrical Pt10Ir electrodes [photo with permission and courtesy of Boston Scientific; ©2022 by Boston Scientific Corporation or its affiliates. All rights reserved.]; f an example of a responsive neurostimulation device (RNS® System, NeuroPace, Inc.; photo used with permission and courtesy of NeuroPace, Inc.); this neurostimulator is implanted in the skull, replacing a similarly shaped section of bone. The cortical strip or depth electrodes (Pt10Ir alloy) are implanted in or on the epileptic seizure focus