Chen A C, Shimojo M, Svensson P, Arendt-Nielsen L
Human Brain Mapping and Cortical Imaging Laboratory, Center for Sensory-Motor Interaction, Aalborg University, Denmark.
Brain Topogr. 2000 Fall;13(1):59-72. doi: 10.1023/a:1007886303206.
Temporal summation is a potent central somatosensory mechanism and may be a major mechanism involved in e.g. neuropathic pain. This study assessed the long-latency somatosensory evoked potentials (SEPs) in response to trains of repeated painful electrical stimulation of human skin and muscle in order to investigate the cerebral representation of temporal summation. Forty series of stimuli were delivered at stimulus intensities corresponding to moderate pain levels in 20 young men. Each series consisted of a five-burst-pulses (1 ms) train delivered at 2 Hz, known to activate temporal summation, i.e. increased pain intensity during the series of stimuli. Grand mean averaged waveforms (31 ch. EEG) were obtained in response to the skin and muscle stimulation. In the "train" SEPs, the wave morphology was characterized by four peak components after the first stimulus (100 to 450 ms) and by three components after the fifth stimulus (2100-2145 ms). The latency was significantly prolonged for muscle stimulation only. The 3D topographic maps at the peak activation time (100, 140, 250, and 450 ms) showed clear reduction in the amplitudes and their spatial extent (P4/P100-Fc2/N100, POz/P140-Fc2/N140, Cz/P250, Cz/N460) betweenthe first and the fifth stimulus. The current source density (CSD) topology exhibited markedly differential patterns changing from the first to the fifth stimulus. For the skin stimulation, the fifth stimulus was associated with a distinct emergence of the frontal negativity source at Fc2 right frontal cortex. This was consistent across the 100,140, 250, and 450 peak components but was not even visible in the first stimulus. In the muscle, the fifth stimulus was associated with a marked reduction of the frontal positivity at contralateral F4 site in the early stages at 100 and 140 ms, and with a total disappearance of positive source at Cz. In summary, this study demonstrated a clear temporal summation of psychophysical ratings, reduction of the peak amplitudes in the last of the first stimuli, dissociation from simple amplitude increase of the cerebral responses to pain, and a concurrent transformation of the CSD patterns. This change in "rapid cortical dynamics" of short-term plasticity could be an important mechanism for wind-up and pain processing in the brain.
时间总和是一种强大的中枢躯体感觉机制，可能是诸如神经性疼痛等所涉及的主要机制。本研究评估了人类皮肤和肌肉重复疼痛性电刺激序列所诱发的长潜伏期躯体感觉诱发电位（SEP），以研究时间总和的脑表征。在20名年轻男性中，以对应中度疼痛水平的刺激强度给予40组刺激。每组刺激由以2Hz频率发放的一串五个脉冲（1ms）组成，已知该频率可激活时间总和，即在刺激序列中疼痛强度增加。记录了对皮肤和肌肉刺激的平均总波形（31导脑电图）。在“序列”SEP中，第一个刺激后（100至450ms）的波形形态特征为四个峰值成分，第五个刺激后（2100 - 2145ms）为三个成分。仅肌肉刺激时潜伏期显著延长。在峰值激活时间（100、140、250和450ms）的三维地形图显示，第一个和第五个刺激之间，振幅及其空间范围（P4/P100 - Fc2/N100、POz/P140 - Fc2/N140、Cz/P250、Cz/N460）明显减小。电流源密度（CSD）拓扑结构显示从第一个刺激到第五个刺激有明显不同的模式变化。对于皮肤刺激，第五个刺激与右额叶皮层Fc2处明显出现的额部负性源相关。这在100、140、250和450峰值成分中均一致，但在第一个刺激中甚至不可见。在肌肉中，第五个刺激在100和140ms早期与对侧F4部位的额部正性明显降低相关，且Cz处正性源完全消失。总之，本研究证明了心理物理学评分存在明显的时间总和，第一个刺激序列中最后一个刺激的峰值振幅降低，大脑对疼痛反应的幅度增加与之分离，以及CSD模式同时发生转变。这种短期可塑性“快速皮层动力学”的变化可能是大脑中痛觉增敏和疼痛处理的重要机制。
