• Karl A Sillay, Paul Rutecki, Kathy Cicora, Greg Worrell, Joseph Drazkowski, Jerry J Shih, Ashwini D Sharan, Martha J Morrell, Justin Williams, and Brett Wingeier.
• Department of Neurological Surgery, University of Wisconsin Hospitals and Clinics, Madison, WI, USA; Department of Biomedical Engineering, University of Wisconsin, Madison, WI, USA. Electronic address: ksillay@gmail.com.
• Brain Stimul. 2013 Sep 1;6(5):718-26.

AbstractLong-term stability of the electrode-tissue interface may be required to maintain optimal neural recording with subdural and deep brain implants and to permit appropriate delivery of neuromodulation therapy. Although short-term changes in impedance at the electrode-tissue interface are known to occur, long-term changes in impedance have not previously been examined in detail in humans. To provide further information about short- and long-term impedance changes in chronically implanted electrodes, a dataset from 191 persons with medically intractable epilepsy participating in a trial of an investigational responsive neurostimulation device (the RNS(®) System, NeuroPace, Inc.) was reviewed. Monopolar impedance measurements were available for 391 depth and subdural leads containing a total of 1564 electrodes; measurements were available for median 802 days post-implant (range 28-1634). Although there were statistically significant short-term impedance changes, long-term impedance was stable after one year. Impedances for depth electrodes transiently increased during the third week after lead implantation and impedances for subdural electrodes increased over 12 weeks post-implant, then were stable over the subsequent long-term follow-up. Both depth and subdural electrode impedances demonstrated long-term stability, suggesting that the quality of long-term electrographic recordings (the data used to control responsive brain stimulation) can be maintained over time.Copyright © 2013 Elsevier Inc. All rights reserved.

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