Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Spatial perception is sensitive to the energetic costs required to perform intended actions. For example, hills look steeper to people who are fatigued or burdened by a heavy load. Similarly, perceived distance is also influenced by the energy required to walk or throw to a target. ⋯ In the current paper, we expand on the notion of "cost" by examining perceived distance in patients diagnosed with chronic pain, a multifactorial disease, which is experienced while walking. We found that chronic pain patients perceive target distances to be farther away compared with a control group. These results indicate the physical, and perhaps emotional, costs of chronic pain affect spatial perceptions.
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Capsaicin activates the transient receptor potential vanilloid 1 receptor (TRPV1) on small sensory afferents, and capsaicin is commonly used to elucidate mechanisms of neuropathic pain. This study was performed to describe changes in cold and cold pain perception after topically applied capsaicin. Fourteen healthy subjects were included. ⋯ The skin temperature was kept between 34 and 35 degrees C. At the site of capsaicin application (the primary area), we found profound cold hypoesthesia and hypoalgesia, while outside the application site (the secondary area) there were no difference in the changes in cold detection and cold pain thresholds and cold-induced pain compared to the control arm. These results suggest a peripheral mediated decrease in cold sensation following TPRV1 receptor activation.
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Randomized Controlled Trial Comparative Study
Spatial and temporal aspects of muscle hyperalgesia induced by nerve growth factor in humans.
Intramuscular injection of nerve growth factor (NGF) has been shown to induce long-term sensitisation and time-dependent hyperalgesia indicating potential involvement of both central and peripheral pain mechanisms. This double-blind placebo-controlled study was designed to describe the spatial distribution of muscle hyperalgesia over time (immediately after, 3 h, 1, 4, 7 and 21 days) after injecting NGF (5 mug) into the tibialis anterior (TA) muscle, to explore possibly involved central pain mechanisms and to investigate the effect of gender on development of hyperalgesia. Totally 20 healthy volunteers (10 men and 10 women) participated in the study. ⋯ Injection of NGF increased muscle soreness during muscle activity for 7 days. In this material there was no gender effect of NGF-induced muscle hyperalgesia. The expansion of muscle hyperalgesia to distant areas indicates that central mechanisms are involved.
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Comparative Study
Spatial and temporal acuity of visual perception can be enhanced selectively by attentional set.
The aim of this research was to study the relationship between perceptual judgments about space and time. If spatial and temporal judgments were dissociable, they should be modulated selectively by attention. We compared the effect of the attentional set upon fine-grained spatial versus temporal discrimination of visual perception in two experiments. ⋯ The results showed that the attentional set enhanced the speed and accuracy of perceptual judgments similarly on both spatial and temporal tasks. Moreover, accuracy in one task was selectively enhanced by attending to that task while remaining unaffected by attending to the alternative task. This finding suggests multiple mechanisms, by which visual processing of spatial and temporal features can be selectively prepared without interfering with one another.
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Comparative Study
Effects of experimental pain on jaw muscle activity during goal-directed jaw movements in humans.
To study the effects of masseter muscle pain on jaw muscle electromyographic (EMG) activity during goal-directed tasks. Mandibular movement was tracked and EMG activity was recorded from bilateral masseter, and right posterior temporalis, anterior digastric, and inferior head of lateral pterygoid muscles in 22 asymptomatic subjects at postural jaw position, and during three tasks: (a) protrusion, (b) contralateral (left), (c) open jaw movement. Tasks were performed during three conditions: control (no infusion), test 1 [continuous infusion into right masseter of 4.5% hypertonic saline to achieve 30-60 mm pain intensity on 100-mm visual analog scale (VAS)], and test 2 (isotonic saline infusion; in 16 subjects only); the sequence of hypertonic and isotonic saline was randomized. ⋯ The direction of the hypertonic saline-induced pain effect on EMG activity (i.e., whether the hypertonic saline-induced EMG activity was less than or greater than control EMG activity) could change with the magnitude of jaw displacement. Hypertonic saline infusion had no significant effect on postural EMG activity in any of the recorded jaw muscles. The data suggest that under constrained goal-directed tasks, the pattern of pain-induced changes in jaw muscle EMG activity is not clear cut, but can vary with the task performed, jaw displacement magnitude, and the subject being studied.