BioMag Laboratory, Engineering Centre, Department of Clinical Neurophysiology, University of Helsinki, Helsinki, Finland.
Brain Res. 2010 May 17;1331:74-9. doi: 10.1016/j.brainres.2010.03.058. Epub 2010 Mar 21.
In many animal preparations, repeated stimulation at ca. 10 Hz in thalamic nuclei leads to rapid changes in the cortical evoked responses, known as the augmenting response. The present study was undertaken to evaluate whether anything similar to the augmenting response can be observed in awake human subjects when a peripheral nerve is stimulated, and whether a possible human correlate of augmenting would be modified when the subject is engaged in an active motor task. Somatosensory-evoked magnetic fields (SEFs) were recorded in healthy human subjects in response to stimulus trains (15 pulses at 10 Hz) applied to the left median nerve. SEFs were recorded in a resting condition and during a finger-tapping task performed with the stimulated hand. In the resting condition, the most marked change in the SEF configuration was a reduction of the P35m deflection and a concurrent enhancement of the N45m deflection during the 1st few stimuli of the trains. Another conspicuous feature was a prolongation of the latencies of the N45m and P60m deflections toward the end of the train. In the motor task, the response modulation during the pulse trains was in general similar to the resting condition. The most notable difference was that the P35m amplitude was markedly reduced already for the 1st pulse of the train when compared with rest. Also, the latencies of N45m and P60m were not prolonged during the train. We discuss the possibility that the reduction of P35m and a concurrent increase of N45m during a pulse train constitute a human analogue to the augmenting response, and suggest that these changes may reflect a decrease of inhibitory postsynaptic potentials (IPSPs, P35m) and an increase of secondary excitatory postsynaptic potentials (N45m) during stimulus train presentation. The reduction of P35m during motor activity compared with rest already at the beginning of stimulus trains suggests that postsynaptic IPSPs in response to afferent stimulation are reduced during active movement. Otherwise the short-term plastic changes were similar during rest and motor activity. Finally, the results suggest slowing down of intracortical network processing with repeated stimulation, and that this slowing is not present during an active motor task which depends on afferent feedback information.
在许多动物实验中，对丘脑核团进行约 10 Hz 的重复刺激会导致皮质诱发电响应的快速变化，称为增强响应。本研究旨在评估当外周神经受到刺激时，清醒的人类受试者是否会出现类似的增强响应，以及当受试者进行主动运动任务时，增强响应的可能人类相关物是否会发生变化。在健康的人类受试者中，记录了对左正中神经施加刺激的刺激序列（10 Hz 时 15 个脉冲）的体感诱发电磁场（SEFs）。在休息状态和用受刺激的手进行手指敲击任务时记录 SEFs。在休息状态下，SEF 构型的最显著变化是在刺激序列的前几个刺激中，P35m 偏移量减小，同时 N45m 偏移量增强。另一个显著特征是，随着刺激序列的结束，N45m 和 P60m 潜伏期延长。在运动任务中，脉冲序列期间的响应调制通常与休息状态相似。最显著的区别是，与休息相比，当比较第 1 个脉冲时，P35m 幅度明显减小。此外，在刺激序列期间，N45m 和 P60m 的潜伏期没有延长。我们讨论了在脉冲序列期间 P35m 减少和同时 N45m 增加构成人类增强响应类似物的可能性，并提出这些变化可能反映了刺激序列呈现期间抑制性突触后电位（P35m）的减少和继发性兴奋性突触后电位（N45m）的增加。与休息相比，在运动活动期间 P35m 的减少甚至在刺激序列的开始时就已经表明，在主动运动期间，对传入刺激的突触后 IPSP 减少。否则，在休息和运动活动期间，短期可塑性变化相似。最后，结果表明，随着重复刺激，皮质内网络处理速度减慢，而在依赖传入反馈信息的主动运动任务中，这种速度减慢并不存在。
