Backes W H, Mess W H, van Kranen-Mastenbroek V, Reulen J P
Department of Radiology, Maastricht University Hospital, P.O. Box 5800, 6202 AZ, The, Maastricht, Netherlands.
Clin Neurophysiol. 2000 Oct;111(10):1738-44. doi: 10.1016/s1388-2457(00)00420-x.
The aim of this study was to localize and to investigate response properties of the primary (SI) and the secondary (SII) somatosensory cortex upon median nerve electrical stimulation.
Functional magnetic resonance imaging (fMRI) was used to quantify brain activation under different paradigms using electrical median nerve stimulation in healthy right-handed volunteers. In total 11 subjects were studied using two different stimulus current values in the right hand: at motor threshold (I(max)) and at I(min) (1/2 I(max)). In 7 of these 11 subjects a parametric study was then conducted using 4 stimulus intensities (6/6, 5/6, 4/6 and 3/6 I(max)). Finally, in 10 subjects an attention paradigm in which they had to perform a counting task during stimulation with I(min) was done.
SI activation increased with current amplitude. SI did not show significant activation during stimulation at I(min). SII activation did not depend on current amplitude. Also the posterior parietal cortex appeared to be activated at I(min). The I(min) response in SII significantly increased by selective attention compared to I(min) without attention. At I(max) significant SI activity was observed only in the contralateral hemisphere, the ipsilateral cerebellum, while other areas possibly showed bilateral activation.
Distributed activation in the human somatosensory cortical system due to median nerve stimulation was observed using fMRI. SI, in contrast to SII, appears to be exclusively activated on the contralateral side of the stimulated hand at I(max), in agreement with the concept of SI's important role in processing of proprioceptive input. Only SII remains significantly activated in case of lower current values, which are likely to exclusively stimulate the sensible fibres mediating cutaneous receptor input. Selective attention only enhances SII activity, indicating a higher-order role for SII in the processing of somatosensory input.
本研究旨在定位并研究正中神经电刺激时初级体感皮层（SI）和次级体感皮层（SII）的反应特性。
在健康右利手志愿者中，使用功能性磁共振成像（fMRI）通过正中神经电刺激在不同模式下量化脑激活情况。总共11名受试者参与研究，右手采用两种不同的刺激电流值：运动阈值（I(max)）和I(min)（1/2 I(max)）。在这11名受试者中的7名随后使用4种刺激强度（6/6、5/6、4/6和3/6 I(max)）进行了参数研究。最后，在10名受试者中进行了一项注意力模式研究，即在I(min)刺激期间他们必须执行计数任务。
SI激活随电流幅度增加。在I(min)刺激期间，SI未显示出明显激活。SII激活不依赖于电流幅度。此外，顶叶后皮质在I(min)时似乎也被激活。与无注意力时的I(min)相比，选择性注意力显著增加了SII中的I(min)反应。在I(max)时，仅在对侧半球、同侧小脑观察到显著的SI活动，而其他区域可能显示双侧激活。
使用fMRI观察到由于正中神经刺激在人类体感皮层系统中出现的分布式激活。与SII不同，SI在I(max)时似乎仅在受刺激手的对侧被激活，这与SI在本体感觉输入处理中的重要作用概念一致。在较低电流值情况下，只有SII仍显著激活，这些电流值可能仅刺激介导皮肤感受器输入的感觉纤维。选择性注意力仅增强SII活动，表明SII在体感输入处理中具有更高层次的作用。
