Analysis of somatosensory evoked potentials to lateral popliteal nerve stimulation in man

Abstract

Somatosensory evoked potentials (SEPs) to the lateral popliteal nerve were studied in 41 normal subjects. Analysis of the SEPs was carried out by observing amplitude distribution over the scalp, recovery function and alteration during sleep. 1. 1. The wave form of the SEPs was fairly consistent from subject to subject. The SEP had an initial positive peak (P 1) and a negative peak (N 1) at latencies of approximately 34 and 45 msec, respectively, and five alternative positive and negative peaks (P 2, N 2, P 3, N 3 and P 4). For the sake of description, the response was divided into four components (components 1, 2, 3, and 4), each having the peak at P 1, P 2, P 3 and P 4, respectively. 2. 2. Scalp distribution of component 1 was restricted in the parietal area just posterior to the vertex, whereas that of component 2 was shifted more anteriorly. Component 3 had the widest distribution among all. Component 4 showed the next widest symmetrical distribution with the maximum at the vertex. 3. 3. After maximal excitation, components 1 and 2 recovered the control responsiveness at approximately 200 msec and 600 msec, respectively. Components 3 and 4 had much slower recovery processes. These components were still depressed even at 800 msec. 4. 4. When sleep progressed from stage 1 to stage 2 and further stage 3, component 1 was decreased without changing its peak latency, and the peak latency of component 2 was prolonged with an increase in amplitude. 5. 5. By comparison with the results of previous studies in animal and man, it was inferred the component 1 would be the postsynaptic potential of the primary response mediated by the specific thalamo-cortical projection system and would correspond to the component 2 of the medial nerve SEP as established by Allison (1962) and Goff et al. (1962). Component 2 may correspond to the association response of Amassian (1954). Component 3 may probably be related to the non-specific diffuse projection system. Component 4 may represent the positive phase of the V-potential.