Electrical stimulation of excitable tissue: design of efficacious and safe protocols.

Electrical stimulation of nerve tissue and recording of neural electrical activity are the basis of emerging prostheses and treatments for spinal cord injury, stroke, sensory deficits, and neurological disorders. An understanding of the electrochemical mechanisms underlying the behavior of neural stimulation and recording electrodes is important for the development of chronically implanted devices, particularly those employing large numbers of microelectrodes. For stimulation, materials that support charge injection by capacitive and faradaic mechanisms are available. These include titanium nitride, platinum, and iridium oxide, each with certain advantages and limitations. The use of charge-balanced waveforms and maximum electrochemical potential excursions as criteria for reversible charge injection with these electrode materials are described and critiqued. Techniques for characterizing electrochemical properties relevant to stimulation and recording are described with examples of differences in the in vitro and in vivo response of electrodes.

https://www.annualreviews.org/doi/pdf/10.1146/annurev.bioeng.10.061807.160518

Neural stimulation and recording electrodes.

Stimulating electrodes of various sizes were used to investigate the interactions of two stimulus parameters, charge density and charge per phase, in determining the threshold of neural injury induced by electrical stimulation. Platinum electrodes ranging in size from 0.002 to 0.5 cm/sup 2/ were implanted over the parietal cortex of adult cats. Ten days after implantation, the electrodes were pulsed continuously for 7 h using charge-balanced, current-regulated, symmetric pulse pairs 400 mu s per phase in duration and at a repetition rate of 50 Hz. The results show that charge density (as measured at the surface of the stimulating electrode) and charge per phase interact in a synergistic manner to determine the threshold of stimulation-induced neural injury. This interaction occurs over a wide range of both parameters: for charge density from at least 10 to 800 mu C/cm/sup 2/, and for charge per phase from at least 0.05 to 5.0 mu C per phase. The significance of these findings in elucidating the mechanisms underlying stimulation-induced injury is discussed. >

Charge density and charge per phase as cofactors in neural injury induced by electrical stimulation

Electrical stimulation of neural tissue to evoke behavioral responses

Retinal Prosthesis for the Blind

Electrical stimulation of the nervous system is of increasing importance for a variety of prospective neural prostheses. Electrochemical reactions which may occur at Pt or other noble metal-tissue interfaces are reviewed. Use of stimulus waveforms with a net direct current component increases the probability of tissue damage. There are three conceptually safe methods of injecting charge from a noble metal into tissue: modification of the electrical double layer at the interface and coupling via either of two symmetrical surface-layer oxidation-reduction processes. These reactions may be addressed with stimulus waveforms without a direct current component and with controlled charge densities.

S. B. Brummer

Papers

Electrochemical Considerations for Safe Electrical Stimulation of the Nervous System with Platinum Electrodes