Effect of frequency stimulation on latency and amplitude of long-latency median nerve stimulation somatosensory evoked potentials N70

The presence of the N70 long-latency somatosensory evoked potential in patients with postanoxic coma is associated with neurological recovery [2,3]. In this study, we aimed to establish normative amplitude and latency values for the N70 and to assess the influence of stimulus frequency on these values as previously described with others evoked potentials [1]. We prospectively enrolled healthy adults from our Neurology department. We recorded the N70 over C4 or C3 using contralateral ear reference after bilateral median nerve stimulation at two frequencies (0.7Hz and 1.1Hz). For each side and each frequency, two runs of 200 stimuli were delivered and averaged. Two readers manually measured the amplitude and latency of N70. If absent, its amplitude and latency were considered null and not available, respectively. Data from left and right stimulation were pooled and summarized as median and interquartile range [IQR]. Data were analyzed using the Fisher exact test or the Wilcoxon signed rank test. A P-value