Feasibility of differentially measuring afferent and efferent neural activity with a single nerve cuff electrode.

Abstract

OBJECTIVE\nAdvances in electrode technology have facilitated the development of neuroprostheses for restoring motor/sensory function in disabled individuals. Information extracted from whole nerve, recorded using cuffs, can provide signals that control the operation of neuroprostheses. However, the amount of information that can be extracted from a tripolar cuff - which provides the highest signal-to-noise ratio (SNR) - is limited. The physical symmetry of the tripolar cuff results in neural recordings that cannot differentiate afferent vs. efferent signals. In this study, we introduced a tetrapolar cuff to achieve low-noise and directionally-sensitive recording.\n\n\nAPPROACH\nThe tetrapolar cuff was initially designed using a computational approach. A finite element model was used to solve for the electric potential generated at the electrode contacts by active electrical sources, such as the nodes of Ranvier and an artifact noise source. The resulting single fiber action potentials (SFAP) and artifact noise signals (ANS) were used to characterize the performance of the tetrapolar configuration of electrode length (EL) and electrode edge length (EEL) on simulated SFAP and ANS. The feasibility of using tetrapolar cuff to differentiate afferent/efferent action potentials by applying potassium chloride in anesthetized rats was also investigated.\n\n\nMAIN RESULTS\nBoth computational and experimental results of this study indicated that directional recording can be achieved using a tetrapolar cuff. Testing different design criteria (e.g., EL and EEL) showed that at EL values above 15 mm and EEL ≥ 2 mm, the tetrapolar cuffs can yield larger SNR than equally-sized tripolar cuffs.\n\n\nSIGNIFICANCE\nThis study indicated that low-noise directionally-sensitive measurement of neural activity can be achieved with tetrapolar cuff. The experimental results confirmed the feasibility of using tetrapolar cuff to differentiate afferent/efferent signals by applying potassium chloride. Further work is needed to determine whether the tetrapolar cuff can differentiate afferent/efferent physiologically-elicited neural activities.