Human Studies

Extant literature posits that humans experience two types of threat: physical threat and social threat. While describing pain as "physical" or "social" can be helpful for understanding pain origins (i.e., broken bone versus lost relationship), this dichotomy is largely artificial and not particularly helpful for understanding how the human brain experiences pain. One real world example of social exclusion and rejection that is threatening and likely to bring about significant stress is racism. Racism is a system of beliefs, practices, and policies that operates to disadvantage racialized minorities while providing advantage to those with historical power, particularly White people in the United States and most other Western nations. The objective of this Mini-Review is to present evidence in support of the argument that racism promotes physical pain in racialized minorities, which in turn promotes chronic pain disparities. First, we provide a theoretical framework describing how racism is a potent stressor that affects the health and well-being of racialized minorities. We will then address the neurobiological underpinnings linking racism to social threat, as well as that linking social threats and physical pain. Finally, we will discuss how the perception of social threat brought about by racism may undermine pain management efforts.

If touch is perceived as pleasant, it can counteract the experience of pain. However, its pain-inhibitory function might be disturbed in chronic pain and this could contribute to pain-related interference. We investigated the perception of pleasant touch and its brain correlates in chronic back pain patients (CBP) compared to subacute back pain patients (SABP) and healthy controls (HC) using soft brush strokes. CBP showed less positive evaluations of touch. We found the highest activation in somatosensory and insular cortices in CBP, ventral striatum (VS) in SABP, and the orbitofrontal cortex in HC. Brain responses were significantly positively correlated with pleasantness ratings in HC and SABP, but not CBP. Further, the insula responses in CBP were positively correlated with pain-related interference and the VS activation in SABP correlated negatively with affective distress. Brain and behavioral changes in the processing of touch and its pleasantness may be a marker of pain chronicity and raise questions about the therapeutic value of pleasant touch in pain prevention and treatment.

Chronic Overlapping Pain Conditions (COPCs) are a set of painful chronic conditions characterized by high levels of co-occurrence. It has been hypothesized that COPCs co-occur in many cases because of common neurobiological vulnerabilities. In practice, most research on COPCs has focused upon a single index condition with little effort to assess comorbid painful conditions. This likely means that important phenotypic differences within a sample are obscured. The International Classification of Diseases (ICD) coding system contains many diagnostic classifications that may be applied to individual COPCs, but there is currently no agreed upon set of codes for identifying and studying each of the COPCs. Here we seek to address this issue through three related projects: a) we first compile a set of ICD-10 codes from expert panels for ten common COPCs, b) we then use natural language searches of medical records to validate the presence of COPCs in association with the proposed expert codes, c) finally, we apply the resulting codes to a large administrative medical database to derive estimates of overlap between the ten conditions as a demonstration project. The codes presented can facilitate administrative database research on COPCs. Perspective: This article presents a set of ICD-10 codes that researchers can use to explore the presence and overlap of Chronic Overlapping Pain Conditions (COPCs) in administrative databases. This may serve as a tool for estimating samples for research,exploring comorbidities and treatments for individual COPCs, and identifying mechanisms associated with their overlap.

Cold hyperalgesia is an indicator of widespread pain sensitivity and is associated with poor clinical outcomes. Menthol activates TRPM8, a cold-sensing receptor channel. This research evaluated topical menthol as a potential stimulus to be used in the clinical evaluation of cold hyperalgesia.

Recovery from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection appears exponential, leaving a tail of patients reporting various long COVID symptoms including unexplained fatigue/exertional intolerance and dysautonomic and sensory concerns. Indirect evidence links long COVID to incident polyneuropathy affecting the small-fiber (sensory/autonomic) axons.