Intrafascicular electrodes for stimulation and recording from mudpuppy spinal roots

This paper presents a technique for stimulating and recording from multiple intact spinal roots in the in vitro mudpuppy (Necturus maculatus) spinal cord-forearm preparation using fine wire electrodes, a modified intrafascicular electrode. We found that multiple spinal roots of the preparation could be implanted with these modified electrodes for independent stimulation or recording of the roots without inducing mechanical vibrations, disrupting conduction, or obscuring the view of or access to the spinal cord. Recording and stimulation performance using these electrodes was compared with results obtained using conventional hook electrodes. We found that intrafascicular electrodes were more efficient than hook electrodes for stimulating nerve fibers, being able to produce equivalent levels of activation using stimulation levels that were an order of magnitude smaller. Compound action potential signals recorded from electrodes implanted in the spinal roots were found to be larger than those from hook electrodes placed around the corresponding spinal nerve, showing that intrafascicular electrodes are more efficient at recording activity in the nerve. Moreover, it was possible to record evoked activity from cutaneous mechanoreceptors, even though the signal to noise ratio was low. Rough estimates of the conduction velocities for the fastest components in the compound action potentials were calculated and found to be around 17.5 m/s for both dorsal and ventral roots.