The Electrochemistry Of Electrical Stimulation

Compatibility of a chronic neural prosthesis implant requires that the electrical charge necessary for generation of the neural response be delivered without producing toxic reaction products or degrading the electrode. Thus, only chemically reversible processes can be utilized for charge injection. There is a limit to the charge that any electrode material can deliver with only reversible processes. This limit will depend upon the size of the electrode, its geometry, and the parameters of the stimulation waveform. Reversible charge injection limits for cathodal pulses range from 25 pC/cm2 for some Pt electrodes to 3500 pC/cm2 for Ir oxide. Stimulus-related tissue damage originates from both electrochemical and biological mechanisms. For wide use of neural prosthetics, it will be important toidentifythefactorscontributingtobothofthesemechanisms.