European journal of pain : EJP
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Concerning chronic low back pain (CLBP), different cognitive-behavioral models have hypothesized that coping strategies play a role in the chronification of pain by changes in physical activity. Strategies such as avoidance - or persistent coping may be related to changes in (lumbar) muscle activity. ⋯ In CLBP, a maladaptive coping strategy like "catastrophizing" is related to increased lumbar muscle activity, and an adaptive strategy like "distraction" to increased lumbar muscle relaxation during walking.
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Endogenous analgesia (EA) can be reflected by diffuse noxious inhibitory control (DNIC), non-noxious inhibitory control (NNIC) and habituation to repeated painful stimuli. However, the coexistence of these phenomena in a given individual and the degree to which various factors predict their magnitudes have not been fully investigated. Using experimental paradigms of DNIC, NNIC and habituation, the present study explored the relationships between - and the contribution factors to - the magnitude of EA exhibited by healthy volunteers (n=191; 104 F, 87 M) exposed to these three experimental paradigms. Each subject was assigned to all three paradigms (DNIC-tested by co-administering repeated short painful heat stimuli and a conditioning tonic cold pain stimulation; NNIC - tested similarly with the exception of using a painless conditioning stimulation; habituation - tested by applying repeated painful heat stimuli only) in a random order. Pain intensities decreased from baseline in all three paradigms. However, DNIC produced significantly more pain reduction than the other two modes (RM-ANOVA). The magnitude of pain reduction of DNIC was found to be highly correlated with that of NNIC and habituation (r=0.56, p<0.001 for both correlations). A hierarchical regression analysis showed that baseline (p<0.001) and conditioning pain scores (p=0.043) predicted the magnitude of DNIC. A gender split analysis showed that conditioning pain scores served as a predictive factor for men only. ⋯ Under these experimental conditions, different EA conditions seem to be related to each other. High initial pain intensities predict 'effective' DNIC and habituation, whereas intensity of the conditioning stimulus determines the magnitude of DNIC in men only.
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Electrical low-frequency stimulation (LFS) of cutaneous afferents reliably induces long-term depression (LTD) of nociception and pain in man. In this study LFS effects on cerebral activation were investigated by functional magnetic resonance imaging (fMRI). In 17 healthy volunteers, nociceptive fibers of right hand dorsum were electrically stimulated via a concentric electrode. ⋯ The study revealed LTD of pain-related cerebral activation, involving sensory, affective, cognitive, and attentional processes. Positive correlation between pain relief and increased brain activation after LFS may indicate involvement of endogenous pain control mechanisms in LTD. These experiments may help to judge the potency of LTD for future chronic pain treatment.
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In patients with low back pain (LBP), physical functioning may be negatively influenced by both expectations on pain and pain-related fear. It is unclear whether these factors influence both physical functioning in the laboratory as well as in daily life. The aim of this study was to test if a combination of persistent overprediction of pain and fear of movement predicts lab-based performance and whether these factors are relevant for predicting daily-life functioning. ⋯ No significant association between fear and performance or daily-life functioning were found in correct predictors. In contrast to correct predictors, in overpredictors lab-based performance and daily-life functioning was additionally explained by fear of movement. Thus it appears that fear of movement is only predictive of performance in patients with LBP who simultaneously overpredict the consequences of movements in terms of painfulness.
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Patients with neuropathy, report changes in sensory perception, particularly mechanical and thermal allodynia, and spontaneous pain. Similar sensory changes are seen in experimental neuropathies, in which alteration in primary afferent properties can also be determined. The neural correlate of spontaneous pain is ongoing activity in sensory afferents. ⋯ The afferent barrage associated with mechano-cooling-sensitive afferents was increased 26-fold 7 days after nerve injury. We observed no differences in the properties of intact A fibre mechanosensitive afferents. These studies demonstrate for the first time that the altered nociception seen after PSNI is associated with ongoing activity and enhanced cooling-evoked activity in intact C fibre afferents in the saphenous nerve, with no concurrent alteration in A fibre afferents.