A characterization of the effects on neuronal excitability due to prolonged microstimulation with chronically implanted microelectrodes

Localized, long-lasting stimulation-induced depression of neuronal excitability (SIDNE) is a consequence of prolonged, high-frequency microstimulation in the central nervous system (CNS). It represents a persisting refractory state in the neurons and axons near the stimulating microelectrode, that occurs in the absence of histologically detectable tissue injury. It does not involve a change in synaptic efficacy and, in this respect, it differs from the more familiar phenomenon of long-term depression (LTD). Although SIDNE is ultimately reversible (after several days), it must be taken into account in the design of neural prostheses based on microstimulation in the central nervous system and in animal studies that require prolonged microstimulation in the CNS. In this study, we have characterized the phenomenon, using as the paradigm, iridium microelectrodes implanted chronically in the cat's posteroventral cochlear nucleus. Although the SIDNE may persist for several days after the end of the stimulation protocol, it does not become more severe from day to day when the stimulation protocol is repeated on successive days. The severity of the SIDNE is strongly dependent upon both the instantaneous frequency and the duty cycle of the electrical stimulation. The character of the SIDNE, including its localization to the immediate vicinity of the stimulating microelectrodes, suggests that the phenomenon is a direct consequence of the prolonged electrical excitation of the neurons close to the microelectrode. The problem of designing microstimulation systems that allow high-frequency stimulation of a neural substrate, while minimizing SIDNE are discussed.

[1]  X. Beebe,et al.  Charge injection limits of activated iridium oxide electrodes with 0.2 ms pulses in bicarbonate buffered saline (neurological stimulation application) , 1988, IEEE Transactions on Biomedical Engineering.

[2]  Hambrecht Ft Visual prostheses based on direct interfaces with the visual system. , 1995 .

[3]  M E Greenberg,et al.  Calcium signaling in neurons: molecular mechanisms and cellular consequences. , 1995, Science.

[4]  D. McCreery,et al.  Stimulation with chronically implanted microelectrodes in the cochlear nucleus of the cat: Histologic and physiologic effects , 1992, Hearing Research.

[5]  W. Abraham,et al.  Flip side of synaptic plasticity: Long‐term depression mechanisms in the hippocampus , 1994, Hippocampus.

[6]  D. McCreery,et al.  Stimulus parameters affecting tissue injury during microstimulation in the cochlear nucleus of the cat , 1994, Hearing Research.

[7]  D. McCreery,et al.  A microelectrode for delivery of defined charge densities , 1983, Journal of Neuroscience Methods.

[8]  S. B. Brummer,et al.  Activated Ir: An Electrode Suitable for Reversible Charge Injection in Saline Solution , 1983 .

[9]  F T Hambrecht Visual prostheses based on direct interfaces with the visual system. , 1995, Bailliere's clinical neurology.

[10]  D. McCreery,et al.  Changes in extracellular potassium and calcium concentration and neural activity during prolonged electrical stimulation of the cat cerebral cortex at defined charge densities , 1983, Experimental Neurology.

[11]  D. McCreery,et al.  Neuronal activity evoked by chronically implanted intracortical microelectrodes , 1986, Experimental Neurology.