Abby Tabor

Evidence for working memory deficits in chronic pain: A systematic review and meta-analysis

&NA; Pooled results from behavioural outcome measures of working memory show chronic pain is associated with impaired working memory. A consistent, moderate significant effect is shown in this systematic review and meta‐analysis of 24 studies. &NA; People with chronic pain commonly report impaired cognitive function. However, to date, there has been no systematic evaluation of the body of literature concerning cognitive impairment and pain. Nor have modern meta‐analytical methods been used to verify and clarify the extent to which cognition may be impaired. The objective of this study was to systematically evaluate and critically appraise the literature concerning working memory function in people with chronic pain. The study was conducted along Cochrane collaboration and Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) statement guidelines. A sensitive search strategy was designed and conducted with the help of an expert librarian using 6 databases. Twenty‐four observational studies evaluating behavioural and/or physiological outcomes in a chronic pain group and a control group met the inclusion criteria. All studies had a high risk of bias, owing primarily to lack of assessor blinding to outcome. High heterogeneity within the field was found with the inclusion of 24 papers using 21 different working memory tests encompassing 9 different working memory constructs and 9 different chronic pain populations. Notwithstanding high heterogeneity, pooled results from behavioural outcomes reflected a consistent, significant moderate effect in favour of better performance by healthy controls and, with the exception of one study, pooled results from physiological outcomes reflected no evidence for an effect. Future research would benefit from the use of clearly defined constructs of working memory, as well as standardised methods of testing.

Do people with chronic pain have impaired executive function? A meta-analytical review

A widely held belief within the clinical community is that chronic pain is associated with cognitive impairment, despite the absence of a definitive systematic review or meta-analysis on the topic. The current systematic review and meta-analysis aimed to establish the current evidence concerning the difference in executive function between people with chronic pain and healthy controls. Six databases were searched for citations related to executive function and chronic pain from inception to June 24, 2013. Two reviewers independently assessed studies for eligibility and extracted relevant data according to the Cochrane Collaboration and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Twenty five studies were included in the review and twenty two studies in the meta-analysis. A small to moderate impairment in executive function performance was found in people with chronic pain across cognitive components, although all studies had a high risk of bias. The current evidence suggests impairment of executive function in people with chronic pain, however, important caveats exist. First, executive function involves many cognitive components and there is no standard test for it. Second, moderators of executive function, such as medication and sleep, were seldom controlled for in studies of executive function performance.

Assessing tactile acuity in rheumatology and musculoskeletal medicine—how reliable are two-point discrimination tests at the neck, hand, back and foot?

OBJECTIVE Chronic pain from rheumatic and musculoskeletal conditions is associated with cortical changes and altered tactile acuity. Tactile acuity is considered a clinical signature of primary somatosensory representation. The two-point discrimination (TPD) threshold is increasingly used both clinically and in research. Remarkably, the reliability and precision of the measure at commonly used sites has not been determined. This study aimed to determine the utility, intra- and inter-rater reliability, bias and variability of TPD threshold assessment at the neck, back, hand and foot using mechanical callipers. METHODS Intra- and inter-rater reliability of TPD was assessed at the back, neck, hand and foot of 28 healthy young adults by 28 clinicians. Each clinician received training in the assessment of TPD using mechanical callipers and following a standardized protocol. Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to assess reliability, bias and variability. RESULTS Intra-rater assessments in all four regions and inter-rater assessments at the neck and foot were reliable (ICC range 0.79-0.86), but large variability was seen in all assessments. Inter-rater assessment of the back (ICC = 0.66) and hand (ICC = 0.62) was deemed unreliable. Negligible systematic bias suggested learning did not affect reliability. CONCLUSION Individual clinicians are able to reliably assess TPD threshold at the neck, back, hand and foot using mechanical callipers. Measures obtained by different clinicians were only reliable for the neck and foot. Large variability was observed in all assessments, which suggests clinicians should be cautious when interpreting changes in tactile acuity in individual patients.

Embodied pain—negotiating the boundaries of possible action

Pain is a protective strategy, which emerges from on-going interaction between body and world. However, pain is often thought of as a unitary output—an end product experienced as an intrusion upon an often unsuspecting perceiver. We know a lot about how nociception relates to pain, informed by both biological and psychological influences, how pain intrudes into awareness, and how it relates to clinical variables, such as suffering and disability. However, despite significant advances, the mechanisms of pain intrusion remain elusive. In this article, we stress a functional view of pain as more than experience, as defensive action operating in the context of uncertain threat. Although traditional characterisations of perception as a product of sensory information have been critiqued, including in pain, there is now a well-advanced contemporary view that all perception is embodied and embedded. Here, embodied is defined by action, the premise that cognition extends beyond the brain so that an ever-changing body is at the core of how our experiences are shaped; this may be the unconscious workings of our immune system or the collaborative efforts made to avoid movement. Embedded refers to the situated interaction between the embodied being and the external environment, in both place (current context) and time (evolutionary context). From this view, all experience is inferential, dynamic, and related to action in the world. Thus, to describe the experience of pain, we must understand it within its evolved, learned, and ultimately threat-defined context. Theories of embodied experience are well advanced elsewhere, most notably in cybernetics, evolutionary biology, and consciousness. Its provenance can be traced to structural psychology, phenomenology, and perception. However, embodied domains have avoided pain, considering it either too simple or paradoxically too difficult. Our embodied view, in many ways, complements the existing literature, supporting the growing understanding of pain as an experience inferred from uncertain information. However, it critically looks to extend this work beyond a passive information processing model that has come to dominate. Here, we emphasise the body, not separate from the brain nor the world, but part of the facility that actively shapes our experience of pain. This perspective defines pain in terms of action: an experience that, as part of a protective strategy, attempts to defend one’s self in the presence of inferred threat. We start with a consideration of the core features of embodied pain. Next, we review the few studies that have been attempted on embodied perception and pain. Finally, we discuss how this approach can be applied usefully to pain, exploring both the research and clinical implications of embodied pain.

Pain: A Statistical Account

Perception is seen as a process that utilises partial and noisy information to construct a coherent understanding of the world. Here we argue that the experience of pain is no different; it is based on incomplete, multimodal information, which is used to estimate potential bodily threat. We outline a Bayesian inference model, incorporating the key components of cue combination, causal inference, and temporal integration, which highlights the statistical problems in everyday perception. It is from this platform that we are able to review the pain literature, providing evidence from experimental, acute, and persistent phenomena to demonstrate the advantages of adopting a statistical account in pain. Our probabilistic conceptualisation suggests a principles-based view of pain, explaining a broad range of experimental and clinical findings and making testable predictions.

The close proximity of threat: altered distance perception in the anticipation of pain

Pain is an experience that powerfully influences the way we interact with our environment. What is less clear is the influence that pain has on the way we perceive our environment. We investigated the effect that the anticipation of experimental pain (THREAT) and its relief (RELIEF) has on the visual perception of space. Eighteen (11F) healthy volunteers estimated the distance to alternating THREAT and RELIEF stimuli that were placed within reachable space. The results determined that the estimated distance to the THREAT stimulus was significantly underestimated in comparison to the RELIEF stimulus. We conclude that pain-evoking stimuli are perceived as closer to the body than otherwise identical pain-relieving stimuli, an important consideration when applied to our decisions and behaviors in relation to the experience of pain.

Perceptual bias in pain: A switch looks closer when it will relieve pain than when it won’t

Summary Pain alters the way the environment is perceived. A pain‐relieving switch looks closer when you are experiencing pain than when you are not. Abstract Pain is fundamental to survival, as are our perceptions of the environment. It is often assumed that we see our world as a read‐out of the sensory information that we receive; yet despite the same physical makeup of our surroundings, individuals perceive differently. What if we “see” our world differently when we experience pain? Until now, the causal effect of experimental pain on the perception of an external stimulus has not been investigated. Eighteen (11 female) healthy volunteers participated in this randomised repeated‐measures experiment, in which participants estimated the distance to a switch placed on the table in front of them. We varied whether or not the switch would instantly stop a stimulus, set to the participant’s pain threshold, being delivered to their hand, and whether or not they were required to reach for the switch. The critical result was a strong interaction between reaching and pain [F(1, 181) = 4.8, P = 0.03], such that when participants experienced pain and were required to reach for a switch that would turn off the experimental stimulus, they judged the distance to that switch to be closer, as compared to the other 3 conditions (mean of the true distance 92.6%, 95% confidence interval 89.7%–95.6%). The judged distance was smaller than estimates in the other 3 conditions (mean ± SD difference >5.7% ± 2.1%, t(181) >3.5, P < 0.01 for all 3 comparisons). We conclude that the perception of distance to an object is modulated by the behavioural relevance of the object to ongoing pain.

Chronic tension-type headache is associated with impaired motor learning.

Background Supraspinal activity-dependent neuroplasticity may be important in the transition from acute to chronic pain. We examined neuroplasticity in a cortical region not considered to be a primary component of the central pain matrix in chronic tension-type headache (CTTH) patients. We hypothesised that neuroplasticity would be exaggerated in CTTH patients compared to healthy controls, which might explain (in part) the development of chronic pain in these individuals. Methods Neuroplasticity was examined following a ballistic motor training task in CTTH patients and control subjects (CS). Changes in peak acceleration (motor learning) and motor-evoked potential (MEP) amplitude evoked by single-pulse transcranial magnetic stimulation were compared. Results CTTH patients showed significantly less motor learning on the training task than CS (mean acceleration increase 87% CTTH, 204% CS, p < .05), and CS but not CTTH patients showed a significant increased MEP amplitude following training (CS: F = 2.9, p < .05; CTTH: F = 1.6, p > .05). Conclusions These findings suggest a deficit in use-dependent neuroplasticity within networks responsible for task performance in CTTH patients which might reflect reciprocal influences between primary motor cortex and interconnected pain processing networks. These findings may help explain the positive effects of facilitatory non-invasive brain stimulation targeting motor areas on chronic pain and help elucidate the mechanisms mediating chronic pain.

Perceptual Inference in Chronic Pain: An Investigation Into the Economy of Action Hypothesis

Objective:The experience of chronic pain critically alters one’s ability to interact with their environment. One fundamental issue that has received little attention, however, is whether chronic pain disrupts how one perceives their environment in the first place. The Economy of Action hypothesis purports that the environment is spatially scaled according to the ability of the observer. Under this hypothesis it has been proposed that the perception of the world is different between those with and without chronic pain. Such a possibility has profound implications for the investigation and treatment of pain. The present investigation tested the application of this hypothesis to a heterogenous chronic pain population. Methods:Individuals with chronic pain (36; 27F) and matched pain-free controls were recruited. Each participant was required to judge the distance to a series of target cones, to which they were to subsequently walk. In addition, at each distance, participants used Numerical Rating Scales to indicate their perceived effort and perceived pain associated with the distance presented. Results:Our findings do not support the Economy of Action hypothesis: there were no significant differences in distance estimates between the chronic pain and pain-free groups (F1,60=0.927; P=0.340). In addition, we found no predictive relationship in the chronic pain group between anticipated pain and estimated distance (F1,154=0.122, P=0.727), nor anticipated effort (1.171, P=0.281) and estimated distance (F1,154=1.171, P=0.281). Discussion:The application of the Economy of Action hypothesis and the notion of spatial perceptual scaling as a means to assess and treat the experience of chronic pain are not supported by the results of this study.

Psychological approaches to coping with pain in later life

A psychological model of coping with the demands of aging is outlined. Chronic pain is conceptualized as a challenge to normal aging, because it threatens identity, risks affective disorder (depression), and interferes with action. The sparse evidence for psychological interventions is reviewed, and a case is made for the types of interventions that should be developed to address the specific presentation of geriatric pain management.