Lower brain-stem origin of the median nerve N18 potential

doi:10.1016/0013-4694(94)90009-4

Electroencephalography and Clinical Neurophysiology

Volume 90, Issue 2, February 1994, Pages 170-172

https://doi.org/10.1016/0013-4694(94)90009-4 Get rights and content

Abstract

A patient undergoing intraoperative median nerve somatosensory evoked potential (MSEP) and brain-stem auditory evoked response (BAER) monitoring showed changes during basilar artery aneurysm clipping. There was loss of the BAER wave V, with preservation of waves I and III. Simultaneously, there also was loss of the MSEP N20 potential, with preservation of the N18, N13 and Erb's point potentials. The patient died and autopsy showed an infarct involving the whole rostro-caudal extent of the pontine tegmentum. This combination of electrophysiologic and pathologic findings may help answer questions regarding the exact generators of different MSEP potentials. In particular, it implies that medullary structures can generate the N18 potential.

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Cited by (13)

Absent median nerve P14 far-field somatosensory evoked potential with persistent tibial nerve P30 component in a patient with ischemic pontine lesion
2011, Neurophysiologie Clinique
Citation Excerpt :
In the later recording session, we found a recovery of the median nerve P14 potential to left median nerve stimulation (Fig. 3). The scalp far-field components recorded to median nerve (P13-14 complex and N18 potential) and tibial nerve (P30 and N33 responses) stimulation are commonly considered as generated in the caudal brainstem [6,1–5]. In our case of pontine ischemic lesion, we found the absence of the P14 component with preserved P13 and N18 potentials to median nerve stimulation and normal P30 and N33 responses to tibial nerve stimulation.
In a patient with an ischemic lesion of the right paramedian region of the pons, somatosensory evoked potential (SEP) recording to median nerve stimulation showed an absent P14 response with still preserved P13 and N18 potentials. The tibial nerve P30 and N33 SEP components were normal. Our results suggest that the median nerve P14 potential, absent in our patient, has a different origin from the tibial nerve P30 response, normal in the present case.
Des potentiels évoqués somesthésiques ont été enregistrés chez une jeune femme présentant une lésion ischémique de la région paramédiale droite de la protubérance. Lors de la stimulation du nerf médian gauche, l’onde P14 était absente alors que les ondes P13 et N18 étaient normales. Lors de la stimulation du nerf tibial postérieur gauche, les ondes P30 et N33 étaient normales. Nos résultats suggèrent dès lors que les ondes P14 et P30 ont des origines différentes.
Re-evaluation of short latency somatosensory evoked potentials (P13, P14 and N18) for brainstem function in children who once suffered from deep coma
2003, Brain and Development
One of the major clinical features of brain death is deep coma. Therefore, we re-evaluated retrospectively electrophysiological examinations of brainstem function in about 31 children who had once suffered from deep coma in order to reveal its pathophysiological characteristics. The patient age at coma ranged from 1 month to 10 years (mean 2 years 1 month). The electrophysiological examinations were performed, including any of short-latency somatosensory evoked potential (SSEP), brainstem auditory evoked potential (BAEP) and blink reflexes. We first compared results between the fair and poor prognostic groups, and then re-evaluated SSEP results on a few severely impaired patients with persistent vegetative state (PVS). Subsequently, SSEP clarified more specific findings for a deep coma condition than BAEP and blink reflex. A lack of P14, N18 and N20, and an amplitude reduction or vagueness of P13 in SSEP in these children strongly suggested high risk in their future neurological prognosis. In conclusion, electrophysiological examinations, especially SSEP (P13, P14 and N18), might be very useful in obtaining a long-term neurological prognosis after deep coma in children.
Topographical features of the sensory-evoked responses in malformed brains
2000, Pediatric Neurology
To reveal the functional organization of the somatosensory area in the dysgenetic cortex, somatosensory-evoked potentials were examined in seven patients with congenital brain anomalies diagnosed by magnetic resonance imaging, including six patients in whom multichannel recordings over the scalp were used. In four patients with polymicrogyria/pachygyria and two with lissencephaly, the early cortical responses, frontal P20 and parietal N20, were absent in the cortex contralateral to the stimulated side. The first cortical response was a positive wave that appeared predominantly over the centroparietal area in five patients, and in the frontal area in the other patient with polymicrogyria/pachygyria. These findings suggest that the differentiated somatosensory function is distributed normally in the centroparietal cortex in most cases of widespread cortical dysplasia. However, the absence of P20/N20 may indicate a hypoplastic central sulcus or functionally undifferentiated subdivision of the somatosensory cortex in these patients. The absence of cortical responses in the patient with holoprosencephaly may correspond with growth failure of the thalamocortical afferent projections in this disorder.
Preserved widespread N18 and progressive loss of P13/14 of median nerve SEPs in a patient with unilateral medial medullary syndrome
1996, Electroencephalography and Clinical Neurophysiology - Evoked Potentials
Median nerve somatosensory evoked potentials (SEPs) in a patient with unilateral medial medullary syndrome of recent onset having an MRI-confirmed lesion at upper medulla were investigated. Cortical N20 following stimulation of the affected limb was extremely depressed and delayed, whereas widespread N18, which was best manifested by the CPi-C2S lead (CPi is centroparietal electrode ipsilateral to the stimulation), showed no significant difference regarding amplitude and duration between affected and non-affected sides. The result supported our previous opinion that the principal part of N18, the broad negativity lasting around 20 ms, originates from the cuneate nucleus at the medullary level. Less steep onset of N18 on the affected side suggested that some structures rostral to the cuneate nucleus, possibly the termination of the overall ascending volley, may contribute to the earliest part of N18. P13/14 on the affected side normally preserved at the first examination progressively declined and finally disappeared after 4 months, which suggested that the major part of P13/14 is generated within caudalmost medial lemniscus, as well as the occurrence of retrograde degeneration of lemniscal fibers.
Somatotopy of human hand somatosensory cortex revealed by dipole source analysis of early somatosensory evoked potentials and 3D-NMR tomography
1995, Electroencephalography and Clinical Neurophysiology/ Evoked Potentials
Somatosensory evoked potentials (SEPs) to median nerve and finger stimulation were analyzed by means of spatio-temporal dipole modelling combined with 3D-NMR tomography in 8 normal subjects. The early SEPs were modelled by 3 equivalent dipoles located in the region of the brain-stem (B) and in the region of the contralateral somatosensory cortex (T and R). Dipole B explained peaks P14 and N18 at the scalp. Dipole T was tangentially oriented and explained the N20-P20, dipole R was radially oriented and modelled the P22. The tangential dipole sources T were located within a distance of 6 mm on the average and all were less than 9 mm from the posterior bank of the central sulcus. In 6 subjects the tangential sources related to finger stimulation arranged along the central sulcus according to the known somatotopy. The radial sources did not show a consistent somatotopic alignment across subjects. We conclude that the combination of dipole source analysis and 3D-NMR tomography is a useful tool for functional localization within the human hand somatosensory cortex.
Evoked potentials in the diagnosis of brain death
2004, Advances in Experimental Medicine and Biology

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Short communicationLower brain-stem origin of the median nerve N18 potential

Abstract

Electroenceph. clin. Neurophysiol.

Electroenceph. clin. Neurophysiol.

Electroenceph. clin. Neurophysiol.

Neurol. Clin.

Electroenceph. clin. Neurophysiol.

Electroenceph. clin. Neurophysiol.

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Lower brain-stem origin of the median nerve N18 potential