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The descending nociceptive inhibitory pathways often malfunction in people with chronic pain. Conditioned pain modulation (CPM) is an experimental evaluation tool for assessing the functioning of these pathways. Spinal cord stimulation (SCS), a well-known treatment option for people with failed back surgery syndrome (FBSS), probably exerts its pain-relieving effect through a complex interplay of segmental and higher-order structures.
Learn More >While several studies have found that chronic pain is characterized by increased cross-network connectivity between salience, sensorimotor, and default mode (DMN) networks, a large sample-size investigation allowing a more reliable evaluation of somatotopic specificity and subgroup analyses with linkage to clinical pain intensity has been lacking. We enrolled healthy adults and a large cohort of patients (N=181) suffering from chronic low back pain (cLBP). To specifically link brain connectivity with clinical pain intensity, patients were scanned at baseline and after performing physical maneuvers that exacerbated pain. Compared to healthy adults, cLBP patients demonstrated increased connectivity between the functionally-localized back representation in primary somatosensory cortex (S1back) and both salience and DMN networks. Pain exacerbation maneuvers increased S1back connectivity to salience network regions, but decreased connectivity to DMN, with greater pain intensity increase associated with greater shifts in these connectivity patterns. Furthermore, only in cLBP patients reporting high pain catastrophizing, DMN connectivity was increased to a cardinal node of the salience network, anterior insula cortex, which was correlated with increased post-maneuver pain in this cLBP subgroup. Hence, increased information transfer between salience processing regions, particularly anterior insula, and DMN may be strongly influenced by pain catastrophizing. Increased information transfer between salience network and S1 likely plays an important role in shifting nociceptive afference away from self-referential processing, re-allocating attentional focus and affective coding of nociceptive afference from specific body areas. These results demonstrate S1 somatotopic specificity for cross-network connectivity in encoding clinical back pain, and moderating influence of catastrophizing for DMN/insula connectivity.
Learn More >Neuropathic mechanisms are involved in burning mouth syndrome (BMS), and variation of the dopamine D2 receptor (DRD2) gene contributes to experimental pain perception. We investigated whether neurophysiologic findings differ in BMS patients compared to healthy controls, and whether 957C>T polymorphism of the DRD2 gene influences thermal sensitivity or pain experience in BMS.
Learn More >Parents play a critical role in children's experience of, and recovery from, chronic pain. Although several parental factors have been linked to child pain and functioning, these factors are typically examined in isolation or as moderators/mediators. Structural equation modeling affords the opportunity to examine the extent to which parental factors are interrelated, and if there are differential associations among parental factors and child outcomes. Based on extant literature, a unified model of parental factors, including chronic pain status, physical functioning, responses to child pain, and psychological factors, and their effect on child pain and functioning, was conceptualized. This model was evaluated using structural equation modeling based on data from 146 dyads recruited from a multidisciplinary pain clinic. Modifications to model iterations were made based on theoretical and statistical justification. The final model revealed associations among all parental factors with significant loadings on child pain and functioning. Findings indicated the conceptual model was supported, with the exception of parent responses to child pain. Findings support inclusion of parent chronic pain status and physical and psychological functioning as part of a comprehensive assessment of youth with chronic pain and may inform new parental intervention targets to improve child outcomes. Perspective: A unified structural equation model indicated parents' own chronic pain characteristics and physical and psychological functioning represent important factors associated with child pain and functioning. Current family-based interventions which often primarily focus on parent responses to child pain may need to be adapted to more comprehensively address parental factors.
Learn More >The lateral habenula encodes aversive stimuli contributing to negative emotional states during drug withdrawal. Here we report that morphine withdrawal in mice leads to microglia adaptations and diminishes glutamatergic transmission onto raphe-projecting lateral habenula neurons. Chemogenetic inhibition of this circuit promotes morphine withdrawal-like social deficits. Morphine withdrawal-driven synaptic plasticity and reduced sociability require tumor necrosis factor-α (TNF-α) release and neuronal TNF receptor 1 activation. Hence, habenular cytokines control synaptic and behavioral adaptations during drug withdrawal.
Learn More >The conceptualization of placebo has changed from inactive pills to a detailed understanding of how patients' perception of receiving a treatment influences pain processing and overall treatment outcome. Large placebo effects were recently demonstrated in chronic neuropathic pain, thereby opening the question of whether placebo effects also apply to orofacial neuropathic pain. In this article, we review the new definitions, magnitude, and social, psychological, neurobiologic, and genetic mechanisms of placebo effects in pain, especially neuropathic pain, to illustrate that placebo effects are not simply response bias but psychoneurobiological phenomena that can be measured at many levels of the neuroaxis. We use this knowledge to carefully illustrate how patients' perceptions of the treatment, the relationship with the health care provider, and the expectations and emotions toward a treatment can influence test and treatment outcome and potentially skew the results if they are not taken into consideration. Orofacial neuropathic pain is a new research area, and we review the status on definition, diagnosis, mechanisms, and pharmacologic treatment of neuropathic pain after trigeminal nerve injury, as this condition may be especially influenced by placebo factors. Finally, we have a detailed discussion of how knowledge of placebo mechanisms may help improve the understanding, diagnosis, and treatment of orofacial neuropathic pain, and we illustrate pitfalls and opportunities of applying this knowledge to the test of dental treatments.
Learn More >It is widely accepted that communication between the nervous and immune systems is involved in the development of chronic pain. At each level of the nervous system, immune cells have been reported to accompany and frequently mediate dysfunction of nociceptive circuitry; however the exact mechanisms are not fully understood. One way to speed up progress in this area is to increase interdisciplinary cross-talk. This review sets out to summarize what pain research has already learnt, or indeed might still learn, from examining peripheral and central nociceptive mechanisms using tools and perspectives from other fields like immunology, inflammation biology or the study of stress.
Learn More >Co-prevalence of chronic pain and post-traumatic stress disorder (PTSD) negatively impacts the course of both disorders. Patients diagnosed with both conditions report greater pain, affective distress and disability when compared to those with either chronic pain or PTSD alone. While the prevalence and complexity of the comorbidity is widely acknowledged, there is a dearth of research examining potential mechanism variables that might account for the relationship between chronic pain and PTSD. The current study utilizes a series of mediation analyses to examine if pain catastrophizing mediates the relationship between PTSD symptomatology and chronic pain outcome.
Learn More >Sleep disturbance and chronic pain are related. The present study evaluated both direct and indirect (mediated) pathways through which sleep disturbance might be related to chronic pain intensity and function.
Learn More >Clinicians report reluctance to deliver opioid-tapering advice to patients with chronic pain, in part due to concerns that patients will be angry and dissatisfied. An experiment was conducted to examine chronic pain patients' emotional and attitudinal responses to simulated opioid-tapering advice. Patients scheduled for an initial assessment at a tertiary pain clinic and currently taking opioid medications for pain (N = 196) were randomly assigned to view video footage of a standardized patient receiving one of three forms of treatment advice: 1) stay on current medication, 2) change to a different pain medication, or 3) taper off pain medications and participate in a CBT-based pain self-management program. Participants reported how positive/enthusiastic, anxious/worried, and angry/irritable they felt in response to the simulated treatment advice, and how satisfied with and willing they would be to accept and follow the advice. Participants expressed more positive emotional and attitudinal responses to simulated opioid-tapering advice than to simulated opioid-maintenance advice. Furthermore, participants' responses to simulated opioid-tapering and opioid-change advice were not significantly different, suggesting that participants responded positively to the prospect of change in treatment strategy. Additional analyses revealed that participants with a longer history of chronic pain and opioid use responded less positively to simulated opioid-tapering advice. The results of this study contribute to our understanding of factors that may shape chronic pain patients' responses to opioid-tapering advice and suggest that patients may respond more positively to opioid tapering advice if it is presented together with an alternative treatment approach.
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