Wave-form characteristics and spatial distribution of evoked spinal electrogram in man

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Abstract
The evoked spinal electrogram (SEG) in man was recorded from the epidural space, applying the technique of continuous epidural block, and compared with cord dorsum potential (CDP) in wakeful rabbits. Wave-form characteristics of the evoked SEG activated by the segmental nerves were almost the same in both cervical and lumbar regions. Somatosensory evoked response from the scalp was clearly demonstrated by stimulation of the tibial nerve and 5th toe skin; the evoked SEG was produced only by stimulation of the former. This finding might indicate that large nerve fibers are more responsible for producing the evoked SEG. Central latencies to the peaks of the 2nd components of the P2 wave were 29-33 and 42-48 ms, in cervical and lumbar enlargements, respectively. This probably indicates the presence of a long feedback loop producing the 2nd components. The amplitude of the N1 wave showed a steeper decline along the spinal cord than that of the P2 deflection, indicating the different origins of these 2 components. Polarity of both the N1 and P2 waves became reversed when the cording electrode was situated in the anterior epidural space. The wave-form characteristics of the evoked SEG in man were very similar to those of the CDP in wakeful rabbits.