Neural generators of N18 and P14 far-field somatosensory evoked potentials studied in patients with lesion of thalamus or thalamo-cortical radiations

doi:10.1016/0013-4694(83)90253-5

Electroencephalography and Clinical Neurophysiology

Volume 56, Issue 4, October 1983, Pages 283-292

https://doi.org/10.1016/0013-4694(83)90253-5 Get rights and content

Abstract

Somatosensory evoked potentials (SEPs) to electrical stimulation of the right or left median nerve were studied in 4 patients with hemianesthesia and a severe thalamic or suprathalamic vascular lesion on one side. The SEPs were recorded with a non-cephalic reference. The normal side of each patient served as his or her own control. The lesion consistently abolished the parietal N20-P27-P45 and the prerolandic P22-N30 SEP components. It did not significantly affect the P9-P11-P14 positive far fields, nor the widespread bilateral N18 SEP component. This allowed N18 features to be studied without interference from cortical components. It is proposed that N18 reflects several deeply located generators in brain stem and/or thalamus whereas N20 represents the earliest cortical response of the contralateral post- central receiving areas.

Résumé

Les potentiels évoqués somesthésiques (PES) à la stimulation électrique du nerf médian gauche ou droit ont été étudiés chez 4 malades avec une lésion vasculaire grave thalamique ou suprathalamique unilatérale et une hémianesthésie clinique. Les PES ont été enregistrés avec référence non-céphalique. Le côté normal a servi de contrôle. La lésion a chaque fois aboli les composantes pariétales N20-P27-P45 et prérolandiques P22-N30. Elle n'a pas modifié significativement les far fields P9-P11-P14, ni la composante diffuse bilatérale N18. Il a donc été possible d'étudier le N18 sans interférence des composantes corticales. Le N18 est produit par plusieurs générateurs profonds situés dans le tronc cérébral et/ou le thalamus, alors que le N20 représente la réponse corticale précoce des aires postcentrales de projection somesthésique.

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In both cases, the site of phase reversal of the thalamic signal corresponding to N18 (Case 1:RTL5 and Case 2:LTL2) spatially corresponded to the thalamic region with the highest probability of connectivity with primary sensory cortex (postcentral gyrus) corresponding to the VPL nucleus of the thalamus (Table 1). Using three independent methods of localizing the VPL nucleus of the thalamus, we not only confirm prior reports which inferred the subcortical, thalamic potential (N18) of the MN-SSEP waveform (Mauguiere and Courjon, 1981; Mauguiere et al., 1983; Noel and Desmedt, 1980), but also provide direct within-subject electrophysiologic confirmation of the accuracy, functional specificity, validity, and reliability of DTI-based segmentation of subcortical anatomy. Because of its non-invasive nature and its wide-spread availability and accessibility, MR-based approaches to studying brain connectivity, including diffusion tensor-based tractography to study anatomic connectivity and resting-state MRI to study functional connectivity, have emerged as the primary means of studying human brain connectivity in the laboratory and in the clinical setting (Mars et al., 2011).
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^☆: This research has been supported by grants from the Fonds de la Recherche Scientifique Médicale, Belgium

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