Mechanisms of electrode induced injury. Part 1: theory

Electrodes are the essential elements of clinical neurophysiology both in recording of neural activity and in functional electrical stimulation of the nervous system. Therefore it is important to understand the potential complications of using electrodes. In this paper, the factors that influence the chance of electrode related injury are discussed from a theoretical standpoint. The mechanical factors, especially pressure related injury, are discussed first, followed by a discussion of injury that is of chemical origin such as contact dermatitis. Next, the ways in which electrical currents flowing from electrodes can cause injury including: Joule heating, electroporation, electroconformational denaturation, and excitatory neurotoxicity are discussed. The differential effects of constant current and constant voltage stimulation on tissue heating are examined, as are the effects of the conductivity and geometric structure of the stimulated tissue. Finally, the effects of electrochemical reactions are discussed both in the context of surface and implanted electrodes.