Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels, Belgium;
J Neurophysiol. 2013 Nov;110(10):2312-24. doi: 10.1152/jn.00137.2013. Epub 2013 Aug 21.
It has been hypothesized that the human cortical responses to nociceptive and nonnociceptive somatosensory inputs differ. Supporting this view, somatosensory-evoked potentials (SEPs) elicited by thermal nociceptive stimuli have been suggested to originate from areas 1 and 2 of the contralateral primary somatosensory (S1), operculo-insular, and cingulate cortices, whereas the early components of nonnociceptive SEPs mainly originate from area 3b of S1. However, to avoid producing a burn lesion, and sensitize or fatigue nociceptors, thermonociceptive SEPs are typically obtained by delivering a small number of stimuli with a large and variable interstimulus interval (ISI). In contrast, the early components of nonnociceptive SEPs are usually obtained by applying many stimuli at a rapid rate. Hence, previously reported differences between nociceptive and nonnociceptive SEPs could be due to differences in signal-to-noise ratio and/or differences in the contribution of cognitive processes related, for example, to arousal and attention. Here, using intraepidermal electrical stimulation to selectively activate Aδ-nociceptors at a fast and constant 1-s ISI, we found that the nociceptive SEPs obtained with a long ISI are no longer identified, indicating that these responses are not obligatory for nociception. Furthermore, using a blind source separation, we found that, unlike the obligatory components of nonnociceptive SEPs, the obligatory components of nociceptive SEPs do not receive a significant contribution from a contralateral source possibly originating from S1. Instead, they were best explained by sources compatible with bilateral operculo-insular and/or cingulate locations. Taken together, our results indicate that the obligatory components of nociceptive and nonnociceptive SEPs are fundamentally different.
据推测，人类对伤害性和非伤害性躯体感觉输入的皮质反应不同。支持这种观点的是，由热伤害性刺激引起的躯体感觉诱发电位（SEP）被认为起源于对侧初级躯体感觉（S1）的 1 和 2 区、岛盖和扣带回皮质，而非伤害性 SEP 的早期成分主要起源于 S1 的 3b 区。然而，为了避免产生烧伤损伤，并使伤害感受器敏化或疲劳，通常通过用大的、可变的刺激间隔（ISI）传递少量刺激来获得热伤害性 SEP。相比之下，非伤害性 SEP 的早期成分通常通过快速施加许多刺激来获得。因此，以前报告的伤害性和非伤害性 SEP 之间的差异可能是由于信噪比的差异和/或与觉醒和注意力等相关的认知过程的贡献的差异。在这里，我们使用表皮内电刺激以 1 秒的快速且恒定的 ISI 选择性地激活 Aδ-伤害感受器，发现用长 ISI 获得的伤害性 SEP 不再被识别，这表明这些反应不是伤害感受所必需的。此外，我们使用盲源分离发现，与非伤害性 SEP 的强制性成分不同，伤害性 SEP 的强制性成分没有得到来自可能起源于 S1 的对侧源的显著贡献。相反，它们可以通过与双侧岛盖和/或扣带位置兼容的源得到最好的解释。总之，我们的结果表明，伤害性和非伤害性 SEP 的强制性成分在根本上是不同的。
