Musings of a Compulsive Thinker

Neuroelectric interface example

Here's yet more supporting work for the plug-in prosthesis idea.

Usually, a single nerve supplies several different muscles. Within the nerve are several fascicles, or bundles of nerve fibers; each fascicle supplies a different muscle. (Bear in mind that this is kind of an over-simplification; the nervous system is incredibly complex, and very cool, but we don't need to get into the nitty-gritty details here.) The flat interface nerve electrode, or FINE, is a discriminatory electrode cuff that can interact with selective fascicles within a nerve. More invasive electrodes, ones that are inserted directly into nerve fascicles, perform well but at a high risk for nerve damage. Ideally, for our two-way neuroelectric interface, each electrode will communicate selectively with a small group of nerve fibers within the nerve without damaging the nerve or stimulating non-target fibers ("signal slop").

With the FINE, the working concept is that the cuff puts pressure on the nerve, forcing it to deform into an elongated oval shape, which is a favorable geometry for selective stimulation of fascicles. This effectively increases the nerve's surface area, thereby allowing more electrode contacts to be placed around the nerve; this also causes central nerve fibers, which would otherwise be relatively inaccessible, to move closer to the surface, where they can be more easily stimulated by the contacts.

Leventhal & Durand conducted two separate studies with the FINE. They demonstrated that the FINE was able to selectively activate portions of individual fascicles, and that in general the FINE acted as a stable and selective interface for stimulating peripheral nerves.

Tyler & Durand showed that only the most constrictive (narrow) cuff geometry used in their study was associated with signs of nerve damage (changes in the nerve's function), and that these signs had disappeared by 21 days post-implantation. Their data supported the hypothesis that the constrictive FINE causes an acute initial reaction (due to the high force applied by the cuff) that is resolved over time as the nerve reshapes and intraneural pressure (within the nerve itself) returns to normal. In general, they found that the FINE cuff was able to reshape the nerve and fascicles without significant changes to the nerve's structure and function long-term. Leventhal, Cohen, & Durand found that the "wide" and "medium" cuffs caused little to no damage to nerve fibers and supporting cells; the narrow cuffs were found to cause some damage, which was recovered over the course of the study, which supported Tyler & Durand's findings.

Tyler & Durand: "Chronic Response of the Rat Sciatic Nerve to the Flat Interface Nerve Electrode."

Leventhal & Durand:
"Subfascicle stimulation selectivity with the flat interface nerve electrode."
"Chronic measurement of the stimulation selectivity of the flat interface nerve electrode."

Leventhal, Cohen, & Durand: "Chronic Histological Effects of the Flat Interface Nerve Electrode."

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Labels: engineering, science

posted by the alygator @ 12:38 PM