Quantification of Chronic Microelectrode Signal Quality over Time

The developing field of brain machine interface contains enormous potential for therapeutic benefit. One of the most direct interfaces is the penetrating microelectrode array. However, the failure of chronically implanted neural probes limits the usefulness of penetrating microelectrodes for human brain machine interfaces. Over the course of several weeks after implantation, neural probes lose their ability to record signals due to a variety of tissue reactions including neuronal loss and glial scarring. Several forms of surface enhancements and drug delivery solutions have been proposed. However, in order to systematically evaluate these techniques, a reliable chronic recording model is needed that can offer quantification of recording quality, longevity and reliability. The results of this study are twofold. We present several parameters that may be used as metrics for quantifying the decay of signal quality in a microelectrode array. Second, we consider the effects of a potential surface modification for improving these parameters. In this study, we characterized the quality of neural recordings obtained from microelectrode arrays (16-channel, NeuroNexus, Inc, 16-channel, MicroProbes for Life Science) implanted chronically in the barrel cortex of adult rats. Signal to noise ratio of unit waveforms, local field potential and the ability of the implants to respond to a variety of stimulation parameters were evaluated as measures of the survival of the probe. L1 is a neural adhesion molecule that can specifically promote neurite outgrowth and neuronal survival. Previous in-vitro studies have suggested that that a surface modification of L1 may be able to increase the neuronal density local to the probe. We compared the signal degradation of L1 modified probes and control probes over 8 weeks. The data suggests trends towards improved signal to noise ratio in the L1 coated probes