Changes In Somatosensory Function Research Articles

Exploration of Somatosensory Function of Patients with Acute Non-specific Neck Pain, Through Quantitative Sensory Testing and Self-reported Symptoms.

Adaptations in somatosensory function characterize several chronic pain conditions, including non-specific neck pain (NNP). Early signs of central sensitization (CS) contribute to pain chronification and poor treatment responses after e.g. whiplash injury and low back pain. Despite this well-established association, the prevalence of CS in patients with acute NNP, and accordingly the potential impact of this association, is still unclear. Therefore, this study aims to investigate whether changes in somatosensory function occur during the acute phase of NNP. This cross-sectional study compared 35 patients with acute NNP, with 27 pain-free individuals. All participants completed standardized questionnaires and an extensive multimodal Quantitative Sensory Testing protocol. A secondary comparison was made with 60 patients with chronic WAD, a population wherein CS is well-established. Compared to pain-free individuals, pressure pain thresholds (PPTs) at remote areas and thermal detection and pain thresholds were unaltered. However, patients with acute NNP showed lower cervical PPTs and conditioned pain modulation, and higher temporal summation, Central Sensitization Index (CSI) scores, and pain intensity. Compared to the group with chronic WAD, PPTs did not differ at any location, yet CSI scores were lower. Changes in somatosensory function occur already in acute NNP. Local mechanical hyperalgesia demonstrated peripheral sensitization, while enhanced pain facilitation, impaired conditioned pain modulation, and self-reported symptoms of CS suggest adaptations in pain processing already early in the stage of NNP.

Somatosensory profiling of patients with plaque-induced gingivitis: a case-control study.

This study aimed to assess the mechanical and thermal sensory thresholds of the gingiva in patients with plaque-induced gingivitis compared with a control group to help characterize effects of an inflammatory condition in the oral mucosa on somatosensory function. Quantitative sensory testing (QST) was used in 22 patients (men 10, women 12, age 20-30years) with plaque-induced gingivitis at the lower lateral incisors and in 22 age- and gender-matched healthy volunteers as a control group. One lower lateral incisor (32 or 42) was randomly identified for each included subject. Cold detection threshold (CDT), warm detection threshold (WDT), cold pain threshold (CPT), and heat pain threshold (HPT) of the attached gingiva at the identified lower lateral incisors were assessed in both groups. Pressure pain threshold (PPT) at the teeth was also tested from vertical and lateral directions and analyzed. One-way ANOVA was used to compare the mean values of the identified lower lateral incisors between the two groups. The results showed that the CDT (P = 0.027), WDT (P = 0.021), and HPT (P = 0.005) at the gingiva and PPT (P < 0.001) at the identified lower lateral incisors from the vertical direction were significantly less sensitive, whereas the PPT (P = 0.016) at the gingiva of the identified lateral incisors were significantly more sensitive in the gingivitis group compared to the control group. Plaque-induced gingivitis and the inflammatory response appear to be associated with significant changes in somatosensory sensitivity at the gingiva and periodontal tissue in a bidirectional mode, i.e., both increased and decreased sensitivity to different types of stimuli. Inflammatory reactions in the gingiva seem to be associated with demonstrable changes in somatosensory function including both hypo- and hyperesthesia. These findings may have significance for general oral health and well-being in patients with even plaque-induced gingivitis.

Somatosensory function and pain in extremely preterm young adults from the UK EPICure cohort: sex-dependent differences and impact of neonatal surgery

BackgroundSurgery or multiple procedural interventions in extremely preterm neonates influence neurodevelopmental outcome and may be associated with long-term changes in somatosensory function or pain response. MethodsThis observational study recruited extremely preterm (EP, <26 weeks' gestation; n=102, 60% female) and term-born controls (TC; n=48) aged 18–20 yr from the UK EPICure cohort. Thirty EP but no TC participants had neonatal surgery. Evaluation included: quantitative sensory testing (thenar eminence, chest wall); clinical pain history; questionnaires (intelligence quotient; pain catastrophising; anxiety); and structural brain imaging. ResultsReduced thermal threshold sensitivity in EP vs TC participants persisted at age 18–20 yr. Sex-dependent effects varied with stimulus intensity and were enhanced by neonatal surgery, with reduced threshold sensitivity in EP surgery males but increased sensitivity to prolonged noxious cold in EP surgery females (P<0.01). Sex-dependent differences in thermal sensitivity correlated with smaller amygdala volume (P<0.05) but not current intelligence quotient. While generalised decreased sensitivity encompassed mechanical and thermal modalities in EP surgery males, a mixed pattern of sensory loss and sensory gain persisted adjacent to neonatal scars in males and females. More EP participants reported moderate–severe recurrent pain (22/101 vs 4/48; χ2=0.04) and increased pain intensity correlated with higher anxiety and pain catastrophising. ConclusionsAfter preterm birth and neonatal surgery, different patterns of generalised and local scar-related alterations in somatosensory function persist into early adulthood. Sex-dependent changes in generalised sensitivity may reflect central modulation by affective circuits. Early life experience and sex/gender should be considered when evaluating somatosensory function, pain experience, or future chronic pain risk.

Early changes in somatosensory function in spinal pain: protocol for a systematic review

BackgroundBack and neck pain are common conditions that have a high burden of disease. Changes in somatosensory function in the periphery, the spinal cord and the brain have been well documented at the time when these conditions have become chronic. It is unknown, however, how early these changes occur, what the timecourse is of sensory dysfunction and what the specific nature of these changes are in the first 12 weeks after onset of pain. In this paper, we describe the protocol for a systematic review of the literature on somatosensory dysfunction in the first 12 weeks after pain onset.Methods and designWe will conduct a comprehensive search for articles indexed in the databases Ovid MEDLINE, Ovid Embase, Ovid PsycINFO and Cochrane Central Register of Controlled Trial (CENTRAL) from their inception to August 2013 that report on any aspect of somatosensory function in acute or subacute neck or back pain. Two independent reviewers will screen studies for eligibility, assess risk of bias and extract relevant data. Results will be tabulated and a narrative synthesis of the results conducted.DiscussionCurrently, there is a gap in our knowledge about the timing of somatosensory changes in back and neck pain. The systematic review outlined in this protocol aims to address this knowledge gap and inform developments in diagnostic tools and pain mechanism-based treatments.Trial RegistrationOur protocol has been registered on PROSPERO, CRD42013005113.

Observing motor learning produces somatosensory change

Observing the actions of others has been shown to affect motor learning, but does it have effects on sensory systems as well? It has been recently shown that motor learning that involves actual physical practice is also associated with plasticity in the somatosensory system. Here, we assessed the idea that observational learning likewise changes somatosensory function. We evaluated changes in somatosensory function after human subjects watched videos depicting motor learning. Subjects first observed video recordings of reaching movements either in a clockwise or counterclockwise force field. They were then trained in an actual force-field task that involved a counterclockwise load. Measures of somatosensory function were obtained before and after visual observation and also following force-field learning. Consistent with previous reports, video observation promoted motor learning. We also found that somatosensory function was altered following observational learning, both in direction and in magnitude, in a manner similar to that which occurs when motor learning is achieved through actual physical practice. Observation of the same sequence of movements in a randomized order did not result in somatosensory perceptual change. Observational learning and real physical practice appear to tap into the same capacity for sensory change in that subjects that showed a greater change following observational learning showed a reliably smaller change following physical motor learning. We conclude that effects of observing motor learning extend beyond the boundaries of traditional motor circuits, to include somatosensory representations.

Somatosensory Changes Accompanying Motor Learning

We describe experiments that test the hypothesis that changes in somatosensory function accompany motor learning. We estimated psychophysical functions relating actual and perceived limb position before, and after two kinds of motor learning: directional motor learning (learning to reach in the presence of novel forces applied by a robot), and non-directional learning (learning to reach quickly and accurately to visual targets, without forces). Following force-field learning, sensed limb position shifted reliably in the direction of the applied force. No sensory change was observed when the robot passively moved the hand through the same trajectories as subjects produced during active learning. Perceptual shifts are reflected in subsequent movements: following learning, movements deviate from their pre-learning paths by an amount similar in magnitude and in the same direction as the perceptual shift. After non–directional motor learning in the absence of forces, we observed improvements in somatosensory a...

Resiniferatoxin Induces Paradoxical Changes in Thermal and Mechanical Sensitivities in Rats: Mechanism of Action

Resiniferatoxin (RTX), an ultrapotent analog of capsaicin, has been used as a tool to study the role of capsaicin-sensitive C fibers in pain. Recently, we found that RTX diminished the thermal sensitivity but unexpectedly increased the sensitivity to tactile stimulation in adult rats. In this study, we explored the potential mechanisms involved in RTX-induced changes in somatosensory function. An intraperitoneal injection of 200 microg/kg RTX, but not its vehicle, rapidly produced an increase in the paw withdrawal latency to a heat stimulus. Also, profound tactile allodynia developed in all the RTX-treated rats in 3 weeks. This paradoxical change in thermal and mechanical sensitivities lasted for at least 6 weeks. Electron microscopic examination of the sciatic nerve revealed a loss of unmyelinated fibers and extensive ultrastructural damage of myelinated fibers in RTX-treated rats. Immunofluorescence labeling showed a diminished vanilloid receptor 1 immunoreactivity in dorsal root ganglia neurons and the spinal dorsal horn of RTX-treated rats. Furthermore, two transganglionic tracers, horseradish peroxidase conjugates of cholera toxin B subunit (CTB) and isolectin-B(4) of Bandeiraea simplicifolia (IB(4)), were injected into the opposite sides of the sciatic nerve to trace myelinated and unmyelinated afferent terminations, respectively, in the spinal dorsal horn. In RTX-treated rats, IB(4)-labeled terminals in the dorsal horn were significantly reduced, and CTB-labeled terminals appeared to sprout into lamina II of the spinal dorsal horn. Thus, this study demonstrates that systemic RTX diminishes the thermal pain sensitivity by depletion of unmyelinated afferent neurons. The delayed tactile allodynia induced by RTX is likely attributable to damage to myelinated afferent fibers and their abnormal sprouting in lamina II of the spinal dorsal horn. These data provide new insights into the potential mechanisms of postherpetic neuralgia.

Sensory function above lesion level in spinal cord injury patients with and without pain

Patients with spinal cord injury (SCI) may or may not develop central neuropathic pain despite having cord lesions of apparently the same site, extension and nature. The consequences of the cord lesion in the central nervous system and the mechanisms underlying pain are unclear. In this study, we examined sensory detection and pain thresholds above injury level in 17 SCI patients with central neuropathic pain, in 18 SCI patients without neuropathic pain, and in 20 control subjects without injury and pain. The SCI pain group had significantly higher cold and warm detection thresholds compared with the SCI pain free group and controls and higher tactile detection thresholds compared with the SCI pain free group. No difference in pain or pain tolerance thresholds was seen among pain and pain free SCI patients. These data suggest changes in somatosensory function in dermatomes rostral to the segmental injury level linked to the presence of central neuropathic pain in SCI patients. The results are discussed in relation to current concepts of pain inhibitory and facilitating systems.

Quantification of the hindlimb extensor thrust response in rats.

This report describes a procedure for measuring the extensor thrust response (ETR) and summarizes the results of initial validation experiments using adult Long-Evans rats. The ETR can be quickly elicited and the force measured by pressing against the hindlimb footpads with a small rectangular plate or bar attached to a digital force gauge. Output of the force gauge is analyzed and displayed with commercially available hardware and software. The first experiment compared the acute effects of i.p. injection of chlorpromazine (CPZ; 1, 4, or 7 mg/kg) or amphetamine (AMP; 0.3, 1, or 3 mg/kg) on the ETR and forelimb/hindlimb grip strength (FL/HL-GS) in male and female rats. CPZ decreased both ETR and FL/HL-GS values. Both 1 and 3 mg/kg AMP increased grip strength values but decreased ETR values. A second experiment compared the evolution of changes in ETR, FL/HL-GS, and peripheral neurophysiological measures during 8 weeks of daily oral dosing of 10 mg/kg acrylamide (ACR) monomer. ACR-treated rats exhibited a progressive decrease in ETR beginning after 3 weeks of dosing, whereas a reduction of HL-GS was observed beginning much later, after 7 weeks of dosing. The deficit in ETR progressed in the absence of any changes in spontaneous or evoked electrophysiological abnormalities in neuromuscular function, but was accompanied by a decrease in peripheral nerve conduction velocity. Taken together, the results indicate that the ETR can be used to characterize functional effects in both single dose and repeated dose experiments. The data also indicate that the ETR does not merely duplicate the information provided by FL/HL-GS, and suggest a hypothesis that the ETR may be sensitive to neurotoxicant-induced changes in somatosensory function.