The journal of pain : official journal of the American Pain Society
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The goal in the current study was to examine the analgesic effects of a pinch grip-force production task and a working memory task when pain-eliciting thermal stimulation was delivered simultaneously to the left or right hand during task performance. Control conditions for visual distraction and thermal stimulation were included, and force performance measures and working memory performance measures were collected and analyzed. Our experiments revealed 3 novel findings. First, we showed that accurate isometric force contractions elicit an analgesic effect when pain-eliciting thermal stimulation was delivered during task performance. Second, the magnitude of the analgesic effect was not different when the pain-eliciting stimulus was delivered to the left or right hand during the force task or the working memory task. Third, we found no correlation between analgesia scores during the force task and the working memory task. Our findings have clinical implications for rehabilitation settings because they suggest that acute force production by one limb influences pain perception that is simultaneously experienced in another limb. From a theoretical perspective, we interpret our findings on force and memory driven analgesia in the context of a centralized pain inhibitory response. ⋯ This article shows that force production and working memory have analgesic effects irrespective of which side of the body pain is experienced on. Analgesia scores were not correlated, however, suggesting that some individuals experience more pain relief from a force task as compared to a working memory task and vice versa.
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Review Meta Analysis
Primary motor cortex function in complex regional pain syndrome: a systematic review and meta-analysis.
Dysfunction in the central nervous system is thought to underlie the movement disorders that commonly occur in complex regional pain syndrome (CRPS), with much of the literature focusing on reorganization of the primary motor cortex (M1). Presumed changes in the M1 representation of the CRPS-affected body part have contributed to new CRPS treatments, which are increasingly being integrated in the clinic. We systematically investigated the evidence for altered M1 function in CRPS. We adhered to rigorous systematic review procedure in our search strategy, risk-of-bias appraisal, and data extraction. Eighteen studies comprising 14 unique data sets were included. The included studies used several neuroimaging techniques, whose outcomes we grouped into M1 cortical excitability, spatial representation, reactivity, and glucose metabolism, and conducted meta-analyses where possible. Risk of bias across studies was high, mainly due to missing data and unblinded assessment of outcomes. No definitive conclusions can be drawn regarding M1 spatial representation, reactivity, or glucose metabolism in CRPS. There is limited evidence for bilateral M1 disinhibition in CRPS of the upper limb. ⋯ Despite widely held assumptions of primary motor cortex dysfunction in complex regional pain syndrome, there is only evidence to support bilateral disinhibition, and there is high risk of bias across the literature.
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Pain is ultimately a perceptual phenomenon. It is built from information gathered by specialized pain receptors in tissue, modified by spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with an emotional valence in the brain. Because of this, studying intact animals allows the multidimensional nature of pain to be examined. A number of animal models have been developed, reflecting observations that pain phenotypes are mediated by distinct mechanisms. Animal models of pain are designed to mimic distinct clinical diseases to better evaluate underlying mechanisms and potential treatments. Outcome measures are designed to measure multiple parts of the pain experience, including reflexive hyperalgesia measures, sensory and affective dimensions of pain, and impact of pain on function and quality of life. In this review, we discuss the common methods used for inducing each of the pain phenotypes related to clinical pain syndromes as well as the main behavioral tests for assessing pain in each model. ⋯ Understanding animal models and outcome measures in animals will assist in translating data from basic science to the clinic.
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Vicarious pain has been shown to enhance observers' nociceptive reactivity and pain perception. We exposed healthy participants to specific parts of facial pain expressions in order to investigate which components are required to induce this modulation. We created 2 classes of stimuli: one containing the most useful information for identification of pain expressions (diagnostic) and one containing the least useful information (antidiagnostic). Twenty-eight normal volunteers received electrical stimulation of the sural nerve immediately after they viewed these stimuli. Subjective ratings (intensity and unpleasantness) as well as the nociceptive flexion reflex (NFR) evoked by the shock were recorded. Results show that diagnostic stimuli lead to higher subjective ratings of shock pain than the antidiagnostic stimuli, but the stimuli classes had no significant impact on the NFR. A control experiment showed that our facial stimuli were given very low valence and arousal ratings compared to stimuli previously used to demonstrate the effect of emotional pictures on pain. Thus, the results are unlikely to be explained by emotions felt by the observer and suggest a vicarious facilitation of supraspinal pain processing induced by key features underlying pain expressions recognition. Results provide further support to the perception-action model of empathy. ⋯ This study demonstrates that visual features that are efficiently used for the recognition of pain expressions are sufficient to induce a vicarious facilitation of self-pain. Supraspinal pain responses were modulated by the informativeness of the areas of the pain expressions that participants viewed prior to the painful stimulations.
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Somatic symptoms experienced by women with a menstrually related mood disorder (MRMD) during their premenstrual luteal phase contribute to functional impairment. Yet, investigations on pathophysiological mechanisms contributing to heightened pain sensitivity in MRMD are sparse. During the luteal phase, 61 women with an MRMD and 61 non-MRMD controls were evaluated for β-adrenergic receptor (β-AR) responsivity using the isoproterenol sensitivity test. A subset (43 MRMD and 50 non-MRMD) then entered a double-blind, placebo-controlled, crossover protocol to examine the effect of β-AR blockade with intravenous propranolol on sensitivity to experimental (cold pressor and ischemic) and clinical (McGill Pain Questionnaire score) pain. Women with an MRMD exhibited greater β1- and β2-AR responsivity, ischemic pain intensity, and affective clinical pain ratings than controls. Propranolol increased cold pressor pain tolerance in both groups, but it decreased cold pain intensity and ischemic pain unpleasantness ratings only in non-MRMD women. In contrast, propranolol decreased affective ratings of clinical pain in women with MRMD. Exploratory analyses indicated that only in MRMD women did greater β-AR responsivity predict greater sensitivity to cold pressor and ischemic pain. This study provides the first evidence for a role of β-AR mechanisms in the hyperalgesia and clinical pain experienced by women with MRMDs. ⋯ This article describes the effects of β-adrenergic receptor stimulation and blockade on experimental and clinical pain sensitivity in women with an MRMD. The results of this study may have implications for the management of the substantial somatic premenstrual symptomatology experienced by women with an MRMD.