The sensory origins of human position sense.

KEY POINTS: Position sense at the human forearm can be measured in blindfolded subjects by matching positions of the arms or by a subject pointing to the perceived position of an unseen arm. Effects on position sense tested were: elbow muscle conditioning with a voluntary contraction, muscle vibration, loading the arm and elbow skin stretch. Conditioning contractions and vibration produced errors in a matching task, consistent with the action of muscle spindles as position sensors. Position errors in a pointing task were not consistent with the action of muscle spindles. Loading the arm or skin stretch had no effect in either matching or pointing tasks. It is proposed that there are two kinds of position sense: (i) indicating positions of different body parts relative to one another, using signals from muscle spindles; and (ii) indicating position of the body in extrapersonal space, using signals from exteroceptors, vision, touch and hearing. ABSTRACT: Human limb position sense can be measured in two ways: in a blindfolded matching task, position of one limb is indicated with the other limb. Alternatively, position of a limb, hidden from view, is indicated with a pointer, moved by pressing a lever. These experiments examined the sensory basis of position sense measured in these two ways. Position errors were measured in 14 subjects after elbow flexors or extensors had been conditioned with a half-maximum voluntary contraction. In agreement with previous studies, in the matching trials, position errors were distributed according to a pattern consistent with the action of muscle spindles as the position sensors. In the pointing trials, all errors lay in the direction of extension of the true position of the hidden arm and their distribution was inconsistent with influences arising in muscle spindles. Vibration of elbow muscles produced an illusion of muscle lengthening during a matching task, while during the pointing task no illusion was present. Finally, the matching-pointing error difference was preserved, even when one arm was loaded with a weight or skin over the elbow was stretched. It is proposed that there are two kinds of position sense. One is signalled by muscle spindles, indicating position of one part of the body relative to another. A second provides information about the position of the body in extrapersonal space and here we hypothesise that exteroceptors, including vision, touch and hearing, acting via a central map of the body, provide the spatial information.

Relationship between self-reported cognitive difficulties, objective neuropsychological test performance and psychological distress in chronic pain.

BACKGROUND: Persons with chronic pain often report problems with cognitive abilities, such as memory or attention. There is limited understanding of whether objective performance is consistent with subjective reports, and how psychological factors contribute. We aimed to investigate these relationships in a group of patients expressing cognitive concerns, and evaluate the utility of self-report tools for pain management settings. METHOD: Participants with chronic pain (n = 41) completed standardized neuropsychological tests, and self-report measures of cognitive functioning, pain, mood and sleep, as part of a broader study investigating cognitive performance in pain. RESULTS: Average neuropsychological test performance was subtly below normative means (within one standard deviation). Twenty-five percent of the sample scored substantially below age-adjusted norms on one or more objective tests. There were moderate-to-large associations between objective performance (e.g. Trail-Making B) and subjective cognitive complaints (e.g. Everyday Memory Questionnaire - Revised), controlling for age and education level. This was moderated by anxiety, such that subjective-objective relationships were particularly strong in those with higher anxiety. Poorer test performance was associated with higher pain intensity and catastrophizing. Subjective-objective cognition relationships remained after controlling for catastrophizing. CONCLUSION: Patients' self-reported cognitive concerns concurred with objectively measured performance, independent of age, education and catastrophizing. Moreover, those with severe anxiety were more accurate in predicting their cognitive performance. The findings highlight some interesting cognition-mood relationships, and suggest that easy-to-administer questionnaires, such as the Everyday Memory Questionnaire - Revised and the Behavior Rating Inventory of Executive Function - Adult Version, may be useful to capture cognitive concerns in clinical settings. SIGNIFICANCE: Cognitive concerns in chronic pain reflected objective neurocognitive performance. This was moderated by anxiety, such that self-reported cognition was more consistent with objective performance in those with high anxiety. Our findings suggest that reported cognitive concerns should be heeded, and self-report measures may be used clinically to facilitate dialogue about cognitive functioning.

Financial and recovery worry one year after traumatic injury: A prognostic, registry-based cohort study.

BACKGROUND: Levels of stress post-injury, especially after compensable injury, are known to be associated with worse long-term recovery. It is therefore important to identify how, and in whom, worry and stress manifest post-injury. This study aimed to identify demographic, injury, and compensation factors associated with worry about financial and recovery outcomes 12 months after traumatic injury. METHODS: Participants (n = 433) were recruited from the Victorian Orthopaedic Trauma Outcomes Registry and Victorian State Trauma Registry after admission to a major trauma hospital in Melbourne, Australia. Participants completed questionnaires about pain, compensation experience and psychological wellbeing as part of a registry-based observational study. RESULTS: Linear regressions showed that demographic and injury factors accounted for 11% and 13% of variance in financial and recovery worry, respectively. Specifically, lower education, discharge to inpatient rehabilitation, attributing fault to another and having a compensation claim predicted financial worry. Worry about recovery was only predicted by longer hospital stay and attributing fault to another. In all participants, financial and recovery worry were associated with worse pain (severity, interference, catastrophizing, kinesiophobia, self-efficacy), physical (disability, functioning) and psychological (anxiety, depression, PTSD, perceived injustice) outcomes 12 months post-injury. In participants who had transport (n = 135) or work (n = 22) injury compensation claims, both financial and recovery worry were associated with sustaining permanent impairments, and reporting negative compensation system experience 12 months post-injury. Financial worry 12 months post-injury was associated with not returning to work by 3-6 months post-injury, whereas recovery worry was associated with attributing fault to another, and higher healthcare use at 6-12 months post-injury. CONCLUSIONS: These findings highlight the important contribution of factors other than injury severity, to worry about finances and recovery post-injury. Having a compensation claim, failure to return to work and experiencing pain and psychological symptoms also contribute to elevated worry. As these factors explained less than half of the variance in worry, however, other factors not measured in this study must play a role. As worry may increase the risk of developing secondary mental health conditions, timely access to financial, rehabilitation and psychological supports should be provided to people who are not coping after injury.

Location, location, location: Variation in sensitivity to pain across the body.

BACKGROUND: There is evidence that sensitivity to noxious stimuli differs between the sexes and across the body, but few studies have investigated differences in the perception and experience of acute pain stimuli across the body in healthy individuals. METHODS: We recruited 52 healthy participants, aged 18-36 (50% men) and administered 39, 42 and 45 °C stimuli at four body sites bilaterally to examine differences in the experience of pain intensity and unpleasantness between body sites via an 11-point numerical rating scale. RESULTS: Noxious and innocuous thermal heat stimuli were perceived as significantly more intense when delivered to the wrist (M = 3.98, SD = 1.93) and back (M = 4.07, SD = 1.98) compared to the shoulder (M = 3.45, SD = 1.91) and leg (M = 3.46, SD = 1.87). Pain unpleasantness ratings yielded similar findings; stimuli were perceived as more unpleasant when administered to the wrist (M = 2.83, SD = 1.93) and lower back (M = 3.04, SD = 2.11) compared to the shoulder (M = 2.63, SD = 1.85) and leg (M = 2.26, SD = 1.82). CONCLUSIONS: These findings suggest that painful thermal stimuli delivered to the wrist and back are perceived as more intense and unpleasant compared with other body sites in healthy persons. These differences may be due to variations in receptor density, or the relative importance of these sites for daily living and survival. SIGNIFICANCE: Moreover, these insights are helpful for the design of studies investigating pain experience in healthy persons in experimental or clinical settings. WHAT DOES THIS STUDY ADD?: We tested sensitivity to acute suprathreshold thermal stimulations across a range of body sites to investigate for potential variability. We found significant differences in the perceived intensity and unpleasantness of noxious and innocuous thermal stimuli at the wrist and lower back, compared with the shoulder and leg. These results suggest that pain experience is driven by receptor density or the relative functional importance of these sites.

Sensing the body in chronic pain: a review of psychophysical studies implicating altered body representation.

There is growing evidence that chronic pain conditions can have an associated central pathology, involving both cortical reorganisation and an incongruence between expected and actual sensory-motor feedback. While such findings are primarily driven by the recent proliferation of neuroimaging studies, the psychophysical tasks that complement those investigations have received little attention. In this review, we discuss the literature that involves the subjective appraisal of body representation in patients with chronic pain. We do so by examining three broad sensory systems that form the foundations of the sense of physical self in patients with common chronic pain disorders: (i) reweighting of proprioceptive information; (ii) altered sensitivity to exteroceptive stimuli; and, (iii) disturbed interoceptive awareness of the state of the body. Such findings present compelling evidence for a multisensory and multimodal approach to therapies for chronic pain disorders.

Affective, sensory and empathic sharing of another's pain: The Empathy for Pain Scale.

BACKGROUND: Through two studies, we introduce and validate the Empathy for Pain Scale (EPS), which characterizes the phenomenology of empathy for pain, including the vicarious experience of pain when seeing others in pain. METHODS: In study 1, 406 individuals completed the EPS and Interpersonal Reactivity Index (IRI). In the EPS, four painful scenarios (witnessing surgery, patient recovering from surgery, assault and accidental injury) were rated for 12 emotional, empathic and sensory responses. In study 2, 59 participants completed the same questionnaires and then watched and rated videos of sporting injuries. RESULTS: In study 1, we identified three factors of the EPS with principal component analysis, which were validated with confirmatory factor analysis: affective distress; vicarious pain; and empathic concern. The EPS demonstrated good psychometric properties, re-test reliability (n = 105) and concurrent validity. In study 2, we validated the EPS against empathic reactions to the pain of others as displayed in video clips depicting sporting injuries and showed that the scale has unique utility to characterize empathic reactions to pain above general trait empathy measures. Both studies showed that the affective distress and empathic concern subscales of the EPS correlated with measures of cognitive and affective empathy from the IRI, whereas the vicarious pain subscale was only correlated with the personal distress IRI subscale. CONCLUSIONS: The EPS is a psychometrically sound new scale that characterizes empathy for pain and vicarious pain. The EPS offers valuable insight to the phenomenological profile of the affective, empathic and sensory dimensions of empathy for pain.