-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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