Somatosensory & motor research
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The thermosensory system was evaluated psychophysically in 12 healthy volunteers, spanning the full range of tolerable temperatures. Subjects provided ratings of (1) perceived thermal intensity, (2) perceived pleasantness or unpleasantness, and (3) perceived pain intensity after placing either one hand or foot in a temperature controlled water bath. Of particular interest were the interrelationships among the three perceptual measures, and differences between heat and cold. ⋯ In contrast, there was no significant body site difference for pain intensity or unpleasantness ratings of cold stimuli. All of these results reveal important differences in the processing of cold vs hot stimuli. These differences could be exploited to differentiate processing relevant to discriminative vs affective components of somesthetic perception, in both the innocuous and noxious ranges.
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Clinical Trial
Sensory function above lesion level in spinal cord injury patients with and without pain.
Patients with spinal cord injury (SCI) may or may not develop central neuropathic pain despite having cord lesions of apparently the same site, extension and nature. The consequences of the cord lesion in the central nervous system and the mechanisms underlying pain are unclear. In this study, we examined sensory detection and pain thresholds above injury level in 17 SCI patients with central neuropathic pain, in 18 SCI patients without neuropathic pain, and in 20 control subjects without injury and pain. ⋯ No difference in pain or pain tolerance thresholds was seen among pain and pain free SCI patients. These data suggest changes in somatosensory function in dermatomes rostral to the segmental injury level linked to the presence of central neuropathic pain in SCI patients. The results are discussed in relation to current concepts of pain inhibitory and facilitating systems.
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It has been postulated that peripheral large fiber stimulation could modulate pain perception, probably by gating the input from AS-and C-fibers. The present study examined the effects of concurrent large fiber stimulation on the perception and neurophysiological correlates of brief CO2 laser stimuli known to activate A- and C-nociceptor endings selectively. Four test stimuli of brief non-painful and painful CO2 laser pulses (duration 50 ms; diameter 5 mm; intensity range 0.116-0.212J) were delivered at random every 5-10s on the dorsum of the left forearm of ten healthy subjects. ⋯ Interestingly, the stimulus-response curve of detected stimuli and late LTPs did not change significantly. SDT analysis showed that segmental brushing did not change the discrimination performance or sensitivity but increased significantly the subject's decision criterion for reporting sensation. It was concluded that segmental brushing acted primarily at supra-spinal levels and not by gating the input from small primary afferents activated selectively by brief CO2 laser stimuli.