Do we activate specifically somatosensory thin fibres with the concentric planar electrode? A scalp and intracranial EEG study

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• 作者：Caroline Perchet^a ; ^{caroline.perchet@univ-lyon1.fr} ; Maud Frot^a ; Audran Charmarty^a ; Cecilia Flores^a ; ^b ; Stephanie Mazza^c ; Michel Magnin^a ; Luis Garcia-Larrea^a
• 关键词：Pain ; Evoked potential ; Concentric electrode ; Laser ; Spinothalamic pathway ; Intracerebral recording
• 刊名：Pain
• 出版年：2012
• 期刊代码：214_03043959
• 类别：med
• 出版时间：June, 2012
• 卷：153
• 期：6
• 页码：1244-1252
• 文件大小：807 K

摘要

Laser-evoked potentials (LEPs) are acknowledged as the most reliable laboratory tool for assessing thermal and pain pathways. Electrical stimulation with a newly developed planar concentric electrode, delivering stimuli limited to the superficial skin layers, has been suggested to provide selective activation of A未 fibres without the inconveniences linked to laser stimulation. The aim of our study was to compare the scalp and intracranial responses to planar concentric electrode stimulation (CE-SEPs) with those of LEPs and standard somatosensory-evoked potentials (SEPs). Sixteen healthy subjects, 6 patients with intracortical electrodes, and 2 patients with selective lesions of the spinothalamic pathway were submitted to Neodymium:Yttrium-Aluminium-Perovskite laser stimulations, and electrical stimulations using standard electrodes or planar concentric electrodes (CE). In both healthy controls and epileptic implanted patients, CE- and standard SEPs showed significantly shorter latencies than LEPs. This is consistent with A尾-fibre activation, peripheral activation time being unable to account for longer LEP latencies. In the patients with spinothalamic lesions, LEPs were absent after stimulation of the affected territory, while CE-SEPs were still present. For these 2 reasons, we conclude that the planar CE does not selectively activate the A未 and C fibers, but coexcites a significant proportion of large myelinated A尾 fibres that dominate the ensuing cortical response. The use of CE-SEPs for the detection of spinothalamic system lesions is therefore not warranted; the planar electrode can, however, represent a useful tool to study nociceptive reflexes, which can be reliably elicited even in the presence of A尾 coactivation.