Motor Evoked Potentials Enable Differentiation between Motor and Sensory Branches of Peripheral Nerves in Animal Experiments

Abstract

Differentiation between motor and sensory fascicles is frequently necessary in reconstructive peripheral nerve surgery. The goal of this experimental study was to verify if centrally motor evoked potentials (MEP) could be implemented to differentiate sensory from motor fascicles, despite the well-known intermingling between nerve fascicles along their course to their distant periphery. This new procedure would enable surgeons to use MEP for placing nerve grafts at corresponding fascicles in the proximal and distal stumps without the need to use time-consuming staining. In ten sheep, both ulnar nerves were exposed at the terminal bifurcation between the last sensory and motor branch. Animals were then relaxed to avoid volume conduction. On central stimulation, the evoked nerve compound action potentials were simultaneously recorded from both terminal branches. In all cases, neurogenic motor nerve action potentials were recorded only from the terminal motor branch. The conclusion was that MEPs can be used for intraoperative differentiation between sensory and motor nerves. Further studies are necessary to develop this method for in situ measurements on intact nerve trunks.

Quantitative analysis of motor evoked potentials in the neonatal lamb

“…In our study however, we observed a low intra-individual variability in MEP response in our lambs. This is in concordance with the single previous study on MEP in adult sheep 13 . Similar to previous reports in adult sheep 11 , 46 , 47 , we observed large inter-individual variability 13 , 15 , 45 .…”

“…Non-myogenic MEPs were earlier reported in adult sheep, i.e. epidural recordings after cortical stimulation and peripheral nerve, recordings after transcranial stimulation or muscle recordings after spinal nerve root stimulation 13 , 15 , 45 .…”

“…These electrodes stimulate the brain through the skull, and therefore require high stimulation intensities (up to 900 V) to elicit MEPs 2 . Such a setting has also been used in adult sheep 13 . Since the maximal voltage that our animal stimulator could apply was 120 V, we could not use cork-screw electrodes.…”

Techniques for Differentiating Motor and Sensory Fascicles of a Peripheral Nerve—A Review

“…27 Motor evoked potential (MEP) and somatosensory evoked potential (SSEP) can differentiate between sensory and motor fascicles in animals. 28,29 In MEP, the stimulation is given at the C3/C4 region of the cortex and descending orthodromic nerve action potentials (NAP) can be recorded individually from the separated sensory and motor fascicles of a nerve. The differentiation can be made by noting that the NAP from motor fibers is usually biphasic, short duration, and 3 to 8 times in amplitude than the sensory fibers.…”

Differences in the Structure and Protein Expression of Femoral Nerve Branches in Rats

“…Although peripheral nerve injuries have been studied for decades, their treatment remains a challenge (Sameem et al, 2011). More specifically, there is an inherent difference between sensory and motor nerve fascicles in the peripheral nervous system (PNS; Turkof et al, 2006). Axon regeneration and remyelination underlie peripheral nerve functional recovery following injury (Chen et al, 2007).…”