Using spatial summation of multi-site stimulation electrodes to improve the capability of a sensory neural interface

When afférents reinnervate the muscle tissue nearby a stimulating electrode, it is hard to control how well the single stimulating site of the electrode aligns physically with the location of the nerve fiber. To account for such issues in positioning, a multi-site electrode might aid by delivering electrical stimulation in a distributed fashion. In particular, by sourcing a smaller magnitude of charge per electrode, it may be possible to reduce the likelihood of tissue damage, even while increasing the extent of tissue above the depolarization threshold. Therefore, the work herein develops a finite-element (FE) model of the electrode-muscle interface to determine the distribution of charge density delivered to muscle as a function of two independent variables and their interaction: 1) interelectrode distance and 2) stimulation amplitude. The results indicate that multi-site electrodes can stimulate more muscle volume at lower input amplitude than a single-site electrode, over a range of tissue properties. Importantly, multi-site stimulation may reduce tissue damage and even yet increase the likelihood of stimulating a fiber. Further work is yet needed to tie the modeling results with experimental validation in real tissue.