Skin conductance monitoring is one of the promising methods for objectively evaluating pain. However, skin conductance might possibly increase in response to sympathetic stimulation other than pain. In this study, we aimed to test whether skin conductance monitoring can distinguish physical pain stimulation (heat, mechanical and cold stimulation) from other sympathetic stimuli (stimulation by noise and painful images). Twenty-three healthy volunteers participated in this prospective observational study. The number of fluctuations in skin conductance (NFSC) and normalized skin conductance level (nSCL) were measured and compared with pain scores on a self-reported pain scale (numerical pain scale [NPS]). Both NFSC and nSCL increased during mechanical stimulation. Further, nSCL, but not NFSC, well reflected heat stimulus intensity, suggesting its ability to quantitatively evaluate pain. nSCLs during physical pain stimulation were greater than those during other sympathetic stimulations. However, NFSC was not able to completely distinguish between the stimuli. These results suggest that nSCL could better differentiate physical pain stimuli from other sympathetic stimuli than NFSC. In comparisons between subjective and objective pain assessment in the same individual, nSCL correlated better with NPS score, indicating the possibility of being able to monitor the transition of pain. Monitoring changes in skin conductance using nSCL might be useful for objectively detecting physical pain. Psychometric response scales, such as the visual analogue scale, have been widely used for assessment of pain 1. This seems to be reasonable because the sensation of pain is usually affected by psychogenic factors, including mood, attention, anxiety, expectation, hypnosis and empathy 2. This fact is reflected in the following definition of pain by the International Association for the Study of Pain: An unpleasant sensory and emotional experience with actual or potential tissue damage, or described in terms of such damage 3. However, an objective pain assessment tool is still required, because verbal expression of pain is difficult for certain individuals, such as children, mentally-handicapped persons and intubated and sedated patients. Numerous studies regarding objective pain assessment have been conducted, and several physiological markers of pain, such as heart rate variability and pupillary reflexes, were proposed. However, none of them has been established as a validated marker for pain assessment so far 4,5. Among the different markers proposed, changes in skin conductance might be promising. Activation of sympathetic nerves in the skin following the experience of pain sensation and/or certain emotions, including fear and excitement, results in sweating in the palmar and plantar areas, which in turn increases skin conductance in these areas. Hence, the rationale for development of the skin conductance monitor was to detect changes in skin conductance over time 6. The principle of the skin conductance monitor raised the question r...

BackgroundNeuropathic characteristics are highly involved in the development of chronic pain both physically and psychologically. However, little is known about the relationship between neuropathic characteristics and brain morphological alteration.ObjectivesThe aim of this study is to investigate the mechanisms of chronic pain development by examining the above-mentioned relationships by voxel-based morphometry in patients with chronic pain.MethodsFirst, we assessed neuropathic characteristics using the painDETECT Questionnaire in 12 chronic pain patients. Second, to assess the gray matter volume changes by voxel-based morphometry, we conducted magnetic resonance imaging of the brain. We applied multiregression analysis of these two assessment methods.ResultsThere were significant positive correlations between painDETECT Questionnaire scores and the gray matter volume in the bilateral anterior cingulate cortex and right posterior cingulate cortex.ConclusionsOur findings suggest that neuropathic characteristics strongly affect the brain regions related to modulation of pain in patients with chronic pain and, therefore, contribute to the severity of chronic pain.

Background: Conditioned pain modulation (CPM) is widely used to measure endogenous analgesia, and a recent study indicated that drugs that act on endogenous analgesia are more effective in individuals with lower CPM. Recent animal studies have indicated that pregabalin activates endogenous analgesia by stimulating the descending pain inhibitory system. The present study examined whether the analgesic effect of pregabalin is greater in individuals with lower original endogenous analgesia using CPM. Methods: Fifty-nine healthy subjects were randomly assigned to either a pregabalin group or a placebo group, and 50 of them completed the study. CPM was measured before and after pregabalin or placebo administration. The correlation of initial CPM to change in CPM was compared between the pregabalin and placebo groups. Results: Initial CPM was significantly correlated with the change in CPM in the pregabalin group (r = À0.73, p < 0.0001) but not in the placebo group (p = 0.56) (difference in correlation coefficients between groups; p = 0.004). Furthermore, the initial CPM significantly affected the change in CPM in the pregabalin group but not in the placebo group (pregabalin group: adj R 2 = 0.51, p < 0.001, y = À0.54x + 2.98; placebo group: p = 0.56, significant difference in regression slopes; p = 0.015). These results indicate that pregabalin has a higher endogenous analgesic effect in individuals with lower original endogenous analgesia. Significance: The analgesic effect of pregabalin depends on the original endogenous analgesia status. Its effect on conditioned pain modulation (CPM) was stronger for subjects with lower original endogenous analgesia, suggesting that the mechanism of pregabalin involves the improvement of endogenous analgesia.