Repeated voltage biasing improves unit recordings by reducing resistive tissue impedances

Abstract

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 (Ren) from the model. Implants whose SNR effects lasted more than a day showed stabilized reductions in the extracellular tissue resistance (Rex) and cellular membrane area (Am). 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.

Sources and effects of electrode impedance during deep brain stimulation

“…This effect only occurred in vivo, as they were unable to duplicate these results with an electrode in a saline bath. These results could be explained by work from Johnson et al (Johnson et al, 2005) who found that the most substantial and consistent impedance change came from protein adsorption and the cellular layers surrounding the electrode. In turn, stimulation through a given contact can modify the tissue microstructure of the local encapsulation, increasing conductivity and decreasing electrode impedance.…”

“…Encapsulation is the final stage of the foreign body reaction, wherein the body attempts to destroy or isolate any non-native substance. The tissue response includes both an early antiinflammatory response due to insertion trauma and a sustained response induced in part by the interplay among micromotion, tethering, and device biocompatibility (Johnson et al, 2005). Prior studies have indicated that encapsulation thickness around the DBS electrode lead is at least 25 μm and no greater than 1 mm (Haberler et al, 2000;Hemm et al, 2004).…”

Using a Common Average Reference to Improve Cortical Neuron Recordings From Microelectrode Arrays

“…These requirements would seem to suggest the use of a single microelectrode as a reference, instead of an unmatched larger electrode. Unfortunately, because of the small size of a microelectrode, coupled with fibrous encapsulation endemic to long-term cortical implants (Edell et al 1992;Johnson et al 2005;Ludwig et al 2006;Polikov et al 2005;Schmidt et al 1993;Szarowski et al 2003;Turner et al 1999;Vetter et al 2004;Williams et al 1999;Xindong et al 1999), the impedance of a microelectrode reference adds significant uncorrelated thermal noise to cortical recordings (Kovacs 1994;Schmidt and Humphrey 1990;Shoham and Nagarajan 2003;Webster 1998). Moreover, the microelectrode reference could potentially register neural signal as well as uncorrelated biological noise-adding both to neural recordings.…”

Flexible and Organic Neural Interfaces: A Review

“…Hence, several different approaches have been proposed, including chemical and physical modification of the surface sensing area [50,54], scaling of the sensor size to make the implant less invasive [55], development of more soft, flexible and conformable materials [27,56] and implementation of a rejuvenation protocol to prolong the implant life time [57,58].…”