Modeling study of peripheral nerve recording selectivity

Abstract

Recording of sensory information from afferent fibers can be used as feedback for the closed-loop control of neural prostheses. Clinical applications suggest that recording selectively from various nerve fascicles is important. Current nerve cuff electrodes are generally circular in shape and use a tripolar recording configuration. Preliminary experiments suggest that slowly changing the shape of the nerve to a flatter cross section can improve its selectivity. The objective of this work is to determine the effects of nerve reshaping and other cuff design parameters on the fascicular recording selectivity of a nerve cuff. A finite-element computer model of a multifasciculated nerve with different cuff electrodes was implemented to simulate the recordings. The model included the inhomogeneous and anisotropic properties of peripheral nerves. The recording selectivity was quantified with the use of a Selectivity Index. The results from the model provided information regarding the effect of using monopolar versus tripolar recording configurations, the length of the tripoles in tripolar recordings, the number of contacts that maximize the selectivity index, and the cuff length. Nerve reshaping was found to cause important recording selectivity improvements (106% average). These results provide specific criteria for the design of selectively recording nerve cuff electrodes.

Fascicular Perineurium Thickness, Size, and Position Affect Model Predictions of Neural Excitation

“…A linear fit of the data with the intercept fixed at zero was 2.6% (R 2 = 0.67). The values used in previous computer modeling studies [9], [12], [15], [19], [22], [30] were also compared to the physiologic perineurium thickness measurements in Fig. 3.…”

“…Throughout this study, we used amphibian perineurial conductivity of 0.0021 S/m, which is within the range of 0.0006 to 0.01 S/m used in previous models [9]–[12], [16], [17], [19]. Using the model shown in Fig.…”

“…Previous models examining neural excitation used simplified representations of neural anatomy [2], [9], [11], [12], [14], [19]. Model simplifications included ignoring or fixing the perineurial thickness, ( th p ) using constant fascicle diameter (D f ), and uniformly distributing fascicles within the nerve.…”

“…To further simplify the model, several studies fixed the fascicular size [2], [12], [19], ignoring the physiologic variations in fascicle diameter found within nerves. In these studies, the D f was fixed to 800 μ m [2], [12] or 617 μ m [19].…”

“…In these studies, the D f was fixed to 800 μ m [2], [12] or 617 μ m [19]. Additionally, the fascicles were uniformly spaced within the nerve; another frequent simplification inconsistent with neuroanatomy.…”