Multichannel recording of tibial-nerve somatosensory evoked potentials

Study aims. -The topography of the peaks of tibial.-nerve somatosensory evoked potential (SEP) varies among healthy subjects, most likely because of differences in position and orientation of their cortical generator(s). Therefore, amplitude estimation with a standard one- or two-channel derivation is likely to be inaccurate and might partly cause the low sensitivity of SEP amplitude to pathological changes. In this study, we investigate whether 128-channel tibiat-nerve SEP recordings can improve amplitude estimation and reduce the coefficient of variation. Methods. -We recorded tibial-nerve SEPs using a 128-channel. EEG system in 48 healthy subjects aged 20 to 70 years (47 provided analyzable data). We compared P39, N50, and P60 amplitudes obtained with a 128-channel analysis method (based on butterfly plots and spatial topographies) with those obtained using a one-channel conventional configuration and analysis. Scalp and earlobe references were compared. Results. -Tibial-nerve SEP amplitudes obtained with the 128-channel method were significantly higher as compared to the one-channel conventional method. Consequently, the coefficient of variation was lower for the 128-channel method. In addition, in both methods, the N50-peak amptitude was sometimes hard to identify, because of its low amplitude. Besides, in some subjects, the N50 peak, as obtained with the conventional method, rather seemed to be a period between two positivities rather than an activation peak on itself. Conclusions. -The 128-channel method can measure tibial.-nerve SEP amplitude more accurately and might therefore be more sensitive to pathological changes. Our results indicate that the N50 component is less useful for clinical practice. (c) 2008 Elsevier Masson SAS. All rights reserved.