@misc{oai:ir.soken.ac.jp:00001154, author = {秋, 云海 and シュウ, ウンカイ and QIU, Yunhai}, month = {2016-02-17, 2016-02-17}, note = {It is known that there are two kinds of pain sensation, a sharp or pricking pain associated with rapidly conducting Aδ-fibers (first pain), and a dull or burning pain associated with slowly conducting C-fibers (second pain). We activated C-fibers selectively by stimulating a tiny area of the skin with a CO₂ laser beam using a thin aluminum plate with numerous tiny holes as a spatial filter. Using this new method, we successfully recorded C-fiber discharges with a microneurographic study and cortical responses evoked by C-fiber stimulation using electroencephalography (EEG) and magnetoencephalography (MEG) in humans.
　　　First, we investigated C-fiber discharges and cerebral potentials evoked by weak CO₂ laser beams applied to a tiny skin area in five healthy subjects. Microneurography was recorded from the peroneal nerve in the right popliteal area. Cerebral potentials were recorded from the Cz electrode (vertex, based on the international 10-20 system) referred to linked earlobes. The mean conduction velocity (CV) of the five stable single units was 1.1±0.3 m/s. The mean latency of the positive peak of the cerebral potentials was 1327.4±46.2 ms, which was markedly longer than that from Aδ-fiber stimulation. In contrast, this stimulation method did not activate the Aδ- units at all. These findings indicate that this new stimulation method selectively activates C-fiber nociceptors of the skin (Chapter 5 and Qiu et al., 2003).
　　　Second, we measured the CV of C-fibers in the spinothalamic tract (STT) using this method. We delivered CO₂ laser pulses to tiny areas of the skin overlying the vertebral spinous processes at different levels from the 7^th cervical (C7) to the 12^th thoracic (T12), and recorded the cerebral evoked potentials in 11 healthy men. The mean CV of C-fibers in the STT was 2.2±0.6 m/s, which was significantly slower than that of the Aδ-fibers (10.0±4.5 m/s). This technique is novel and simple, and should be useful as a diagnostic tool for assessing the level of spinal cord lesions (Chapter 6 and Qiu et al., 2001).
　　　Third, we evaluated the effects of attention, distraction and sleep on CO₂ laser-evoked potentials (LEP) related to C-fibers (ultra-late LEP), since the degree of perceived pain sensations is known to be influenced by the subjects’ attention levels. CO₂ laser pulses were delivered to a tiny skin area of the dorsum of the right hand. Ultra-late LEP were recorded from 10 normal subjects in 5 different conditions: control (wakefulness), attention, distraction, drowsiness and sleep (stage 2). The amplitude of ultra-late LEP was slightly increased during attention and significantly decreased during distraction, relative to the control. The ultra-late LEP greatly decreased in amplitude or almost disappeared during sleep. We confirmed that the brain responses related to signals ascending through C-fibers were greatly affected by the level of consciousness, being consistent with the findings of late LEP related to Aδ-fibers. This is the first study indicating the important characteristics of ultra-late LEP related to consciousness, suggesting that they include cognitive function and reporting that one has to be aware of changes in alertness when recording (Chapter 7 and Qiu et al., 2002).
　　　Fourth, using MEG, we evaluated the cerebral regions related to second pain perception ascending through C-fibers and investigated the effect of distraction on each region. Thirteen normal subjects participated in this study. CO₂ laser pulses were delivered to the dorsum of the left hand to selectively activate C-fibers. The MEG responses were analyzed using a multi-dipole model. Results showed that (1) the primary somatosensory cortex (SI), and (2) the secondary somatosensory cortex (SII) - insula were the main generators for the primary component, 1M, the mean peak latency of which was 744 ms. In addition to (1) and (2), (3) the cingulate cortex and (4) the medial temporal area (MT) were also activated for the subsequent component, 2M, the mean peak latency of which was 947 ms. During a mental calculation task (distraction), all six sources were significantly reduced in amplitude, but the SII-insula (P<0.01) and cingulate cortex (P<0.001) were more sensitive than the SI (P<0.05) and MT (P<0.05). We confirmed that the SI in the contralateral hemisphere and the SII-insula, cingulate cortex and MT in the bilateral hemispheres play a major role in second pain perception, and all sites were greatly affected by changes in the attention levels, indicating that these regions are related to the cognitive aspect of second pain perception, and particularly to activities in the cingulate cortex (Chapter 8 and Qiu et al., 2004)., application/pdf, 総研大甲第819号}, title = {SECOND PAIN PROCESSING TRACED BY ELECTRO- AND MAGNETO- ENCEPHALOGRAPHY IN HUMANS}, year = {} }