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Prevertebral (oesophageal) recording of subcortical somatosensory evoked potentials in man: the spinal P13 component and the dual nature of the spinal generators

par Desmedt, Jean Edouard ;Chéron, Guy
Référence Electroencephalography and clinical neurophysiology, 52, 4, page (257-275)
Publication Publié, 1981-10

Article révisé par les pairs

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Résumé :

Short-latency somatosensory evoked potential (SEP) components to median nerve or finger stimulation were recorded in 12 normal young adults with 14 channels, using a noncephalic reference. Several electrodes were placed along the posterior neck, earlobes and scalp while oesophageal probes provided 2-6 recording sites at known levels in front of vertebrae C2 to Th3. The oesophageal electrodes provided a new non-invasive point of entry that secured important data about the generator sources of the spinal SEP components. All cephalic electrodes recorded a P9 far field which is greater over the scalp, earlobes and rostral cervical spine than over the caudal cervical spine. P9 is the volume-conducted peripheral nerve volley coursing between axilla and spinal cord. The direct recording of arrival times of the peripheral volley along the median nerve and brachial plexus (Erb's point) served to estimate the spinal entry time which coincided with the onset of the posterior neck N11 (at levels C6-C7) and of the scalp P11 far field. The latency shift of the onset of N11 from lower to upper neck has been replicated and N11 is interpreted as a presynaptic volley ascending the dorsal column (central branch of the primary neurone) at a velocity of 58 m/sec (Desmedt and Cheron 1980a). At oesophageal electrodes in front of the C7-Th3 vertebrae, the first negative component starts before the spinal entry time and it corresponds to action potentials in the spinal roots. The most remarkable feature of oesophageal recordings in front of the C3 to Th2 vertebrae is the positive P13 component which represented a phase reversal of the second negativity N13 recorded from posterior neck. The P13-N13 phenomenon was recorded in all subjects and presented a stable latency throughout the cervical cord. It was clearly differentiated from the scalp far-field P14 which is related to the ascending volley in the median lemniscus. The spinal P13 did not extend above C2 and it was obviously generated below the foramen magnum. P13 is interpreted as a dorsal horn postsynaptic potential which is elicited by collateral branches of the (bifurcated) primary afferent fibre. The use of 14 simultaneous recordings including a series of pre- and post-vertebral electrodes clearly identified two distinct generators for the spinal SEP components to median nerve stimulation: a presynaptic generator which ascends the dorsal column (N11) and a postsynaptic fixed generator in the dorsal horn of the cervical spinal cord (N13-P13).