Use of laryngeal muscle evoked potential recording for experimental vagus nerve stimulation

The laryngeal muscle evoked potential (LMEP) is a neurophysiological outcome parameter that guarantees integrity of the nerve-electrode interface during experiments with vagus nerve stimulation (VNS). This paper discusses a large series of minimally invasive LMEP recordings in 46 female Lewis rats, implanted with a custom-made VNS electrode around the left cervical vagus nerve. After a 3-week recovery, LMEPs were recorded twice in each animal, with swapping the anode and cathode positions of the VNS electrode (polarity inversion). A VNS-induced LMEP was identified as the initial negative peak wave post-stimulation artifact, consistently recorded in all sweeps at a given stimulation output current. Latency was defined as the time from stimulation onset to this negative peak, and stimulation threshold as the lowest current showing a clear and reproducible LMEP. An LMEP response was shown by 37/46 animals (80.4%), with stimulation intensity threshold of 0.37 ± 0.27 mA and latency of 2.39 ± 0.45 ms. Administering the cathodic pulse phase first at the caudal electrode contact resulted in the shortest LMEP latencies (MWU: p = 0.049. 2.36 ± 0.43 ms vs. 2.41 ± 0.47 ms). Minimally invasive LMEP recording provides a feasible and reliable means for checking electrode functioning and correct implantation.