Pain
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Humans require the ability to discriminate intensities of noxious stimuli to avoid future harm. This discrimination process seems to be biased by an individual's attention to pain and involves modulation of the relative intensity differences between stimuli (ie, Weber fraction). Here, we ask whether attention networks in the brain modulate the discrimination process and investigate the neural correlates reflecting the Weber fraction for pain intensity. ⋯ Of note, this vigilance-related functional coupling specifically predicted participants' behavioral ability to differentiate pain intensities. Moreover, unique to pain discrimination tasks, the response in the right superior frontal gyrus linearly represented the Weber fraction for pain intensity, which significantly biased participants' pain discriminability. These findings suggest that pain intensity discrimination in humans relies on vigilance-related enhancement in the parieto-thalamic attention network, thereby allowing the prefrontal cortex to estimate the relative intensity differences between noxious stimuli.
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Issues of peripheral circulation have been increasingly suggested as an underlying cause of musculoskeletal pain in many conditions, including sickle cell anemia and peripheral vascular disease. We have previously shown in our model of transient ischemia and reperfusion (I/R) injury of the forelimb that individual group III and IV muscle afferents display altered chemosensitivity and mechanical thresholds 1 day after injury. Functional alterations corresponded to increased evoked and spontaneous pain-related behaviors and decreased muscle strength and voluntary activity-all actions that echo clinical symptoms of ischemic myalgia. ⋯ Interleukin 1 receptor antagonist treatment additionally prevented the I/R-induced changes in mechanical and chemical sensitivity of individual primary muscle afferents. Altogether, these data strengthen the evidence that transient I/R injury sensitizes group III and IV muscle afferents via increased IL1β in the muscles to stimulate ischemic myalgia development. Targeting IL1β may, therefore, be an effective treatment strategy for this insidious type of muscle pain.
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The exteroceptive sensory system is responsible for sensing external stimuli in relation to time and space. The aim of this study was to investigate the tempo-spatial properties of the exteroceptive system using painful laser heat and nonpainful mechanical touch stimulation. Thirteen healthy subjects were stimulated on the volar forearm using 2 paradigms: a continuous stimulation along a line on the skin and a 2-point stimulation. ⋯ Numeric rating scale increased both with line length and distance between the 2 points (linear mixed model, P < 0.001). The findings indicate that the tempo-spatial acuity of the exteroceptive system is lower for noxious stimuli than for innocuous stimuli. This is possible due to the larger receptive fields of nociceptive neurons and/or less lateral inhibition.
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Pain and frailty are both prevalent and have severe health impacts among older adults. We conducted a cross-sectional observational study to examine the association between pain and frailty, and depression as a mediator and its interaction with pain on frailty among 1788 Chinese community-dwelling older adults. Physical frailty, pain intensity, and depressive symptoms were assessed using the Frailty Phenotype, the Faces Pain Scale-revised, and the 5-item Geriatric Depression Scale, respectively. ⋯ The relative excess risk of interaction, the attributable proportion due to interaction, and the synergy index (S) were 4.08, 0.50, and 2.34, respectively. These findings suggest that the positive association of pain with frailty is persistent and partially mediated by depression, and comorbid depression and pain have an additive interaction on physical frailty. It has an implication of multidisciplinary care for frail older adults with pain.