Repeated voltage biasing improves unit recordings by reducing resistive tissue impedances

Matthew D. Johnson, Kevin J. Otto, Daryl R. Kipke

Research output: Contribution to journalArticlepeer-review

106 Scopus citations


Reactive tissue encapsulation of chronically implanted microelectrode probes can preclude long-term recording of extracellular action potentials. We investigated an intervention strategy for functionally encapsulated microelectrode sites. This method, known as "rejuvenation," involved applying a +1.5 V dc bias to an iridium site for 4 s. Previous studies have demonstrated that rejuvenation resulted in higher signal-to-noise ratios (SNRs) by decreasing noise levels, and reduced 1-kHz site impedances by decreasing the tissue interface resistances. In this study, we have investigated: 1) the duration of a single-voltage bias session and 2) the efficacy of multiple sessions. These questions were addressed through electrophysiological recordings, cyclic voltammetry, and modeling the electrode-tissue interface via an equivalent circuit model fit to impedance spectroscopy data. In the six implants studied, we found SNRs improved for 1-7 days with a peak typically occurring within 24 h of the voltage bias. Root-mean square (RMS) noise of the extracellular recordings decreased for 1-2 days, which paralleled a similar decrease in the adsorbed tissue resistance (R en) from the model. Implants whose SNR effects lasted more than a day showed stabilized reductions in the extracellular tissue resistance (R ex) and cellular membrane area (A m). Subsequent stimulus sessions were found to drop neural tissue parameters consistently to levels observed immediately after surgery. In most cases, these changes did parallel an improvement in SNR. These findings suggest that rejuvenation may be a useful intervention strategy to prolong the lifetime of chronically implanted microelectrodes

Original languageEnglish (US)
Pages (from-to)160-165
Number of pages6
JournalIEEE Transactions on Neural Systems and Rehabilitation Engineering
Issue number2
StatePublished - Jun 2005

Bibliographical note

Funding Information:
Manuscript received December 8, 2004; revised February 15, 2005; accepted February 21, 2005. This work was supported in part by the Defense Advanced Research Projects Agency under Grant N66001-02-C-8059, in part by the Center for Neural Communication Technology under Grant P41-EB00230, and in part by the Engineering Research Centers program of the National Science Foundation (NSF) under NSF Award Number EEC-9986866.


  • Bias voltage
  • Chronic recording
  • Iridium
  • Microelectrode
  • Neuroprosthesis


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