Pain
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Facial expressions of pain and emotions provide powerful social signals, which impart information about a person's state. Unfortunately, research on pain and emotion expression has been conducted largely in parallel with few bridges allowing for direct comparison of the expressive displays and their impact on observers. Moreover, although facial expressions are highly dynamic, previous research has relied mainly on static photographs. ⋯ Additional rating data further suggest that, for comparable expression intensity, pain is perceived as more arousing and more unpleasant. This study strongly supports the claim that the facial expression of pain is distinct from the expression of basic emotions. This set of dynamic facial expressions provides unique material to explore the psychological and neurobiological processes underlying the perception of pain expression, its impact on the observer, and its role in the regulation of social behaviour.
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Randomized Controlled Trial Clinical Trial
A randomised double blind trial of the effect of pre-emptive epidural ketamine on persistent pain after lower limb amputation.
Persistent pain has been reported in up to 80% of patients after limb amputation. The mechanisms are not fully understood, but nerve injury during amputation is important, with evidence for the crucial involvement of the spinal N-methyl d-aspartate (NMDA) receptor in central changes. The study objective was to assess the effect of pre-emptively modulating sensory input with epidural ketamine (an NMDA antagonist) on post-amputation pain and sensory processing. ⋯ The intrathecal/epidural technique used, with peri-operative sensory attenuation, may have reduced ongoing sensitisation, reducing the overall incidence of persistent pain. The improved short-term analgesia and reduced mechanical sensitivity in Group K may reflect acute effects of ketamine on central sensitisation. Longer term effects on mood were detected in Group K that requires further study.
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This fMRI study investigates the influence of a rating procedure on BOLD signals in common pain-activated cortical brain regions. Painful and non-painful mechanical impact stimuli were applied to the left hand of healthy volunteers. Subjects performed ratings of the perceived intensity during every second stimulation period by operating a visual analogue scale with the right hand. ⋯ Only the responses in the S1 projection field of the stimulated hand following pain were not influenced by the rating procedure. Furthermore, activations in the right and left posterior insular cortex and in the left superior frontal gyrus showed an opposite pattern, namely a stronger BOLD signal during "non-rating". We concluded: (1) Cortical areas regularly activated by painful stimuli may also be activated by touch stimulation. (2) Enhancement of the BOLD contrast by a rating procedure is probably an effect of closer stimulus evaluation and attention focussing. (3) In contrast to most other cortical regions, the posterior insular cortex, which is crucial for the integration of interoceptive afferent input, shows stronger responses in the absence of ratings, which points to a unique role of this region in the processing of somato-visceral information.
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Thermal burns induce pain at the site of injury, mechanical hyperalgesia, associated with a complex time-dependent inflammatory response. To determine the contribution of inflammatory mediators to burn injury-induced mechanical hyperalgesia, we measured dynamic changes in the levels of three potent hyperalgesic cytokines, interleukin IL-1 beta, IL-6, and tumor necrosis factor-alpha (TNFalpha), in skin of the rat, following a partial-thickness burn injury. ⋯ Spinal intrathecal injection of oligodeoxynucleotides antisense for gp130, a receptor subunit shared by members of the IL-6 family of cytokines, attenuated both burn- and intradermal IL-6-induced hyperalgesia, as did intradermal injection of anti-IL-6 function blocking antibodies. These studies suggest that IL-6 is an important mediator of burn-injury pain.