Abstract

Although somatosensory evoked potentials(SSEPs) have been utilized as the useful diagnostic tools in evaluating the wide variety of pathological conditions, such as focal lesions affecting the somatosensory pathways, demyelinating diseases, and detecting the clinically occult abnormality, their neural generators is still considerably uncertain. To appreciate the basis for uncertainties about the origins of SSEPs, consider criteria that must be met to establish a causal relationship between activity in a neural structure and a spine/ scalp-recorded potential. Electrode locations and channel derivations for SSEPs recordings are based on two principles:(1) the waveforms are best recorded from electrode sites on the body surface closest to the presumed generator sources along the somatosensory pathways, and(2) studies of the potential-field distribution of each waveform of interest dictate the best techniques to be used. In this article, authors will describe followings focused on ;(1) the concepts of near field potentials(NFPs) and far field potentials(FFPs) - the voltage of NFPs is highly dependent upon recording electrode position, FFPs are unlike NFPs in that they are widely distributed, their latencies and amplitudes are independent of recording electrode.(2) appropriate montage settings to detect the significant potentials in the median nerve and posterior tibial nerve SSEPs(3) neural generators of various potentials(P9, N13, P14, N18, N20, P37) and their clinical significance in interpretating the results of SSEPs. Especially, Characteristics of N18(longduration, small superimposed inflection) suggested that N18 is a complex wave with multiple generators including brainstem structures and thalamic nuclei. And N18 might be used as the parameter of braindeath. Precise understanding on these facts provide an adequate basis utilizing SSEPs for numerous clinical purposes.

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