Melita J. Giummarra

Phantom limb pain and bodily awareness: current concepts and future directions.

Purpose of review Phantom pain is a frequent consequence of amputation or deafferentation. There are many possible contributing mechanisms, including stump-related pathology, spinal and cortical changes. Phantom limb pain is notoriously difficult to treat. Continued consideration of the factors associated with phantom pain and its treatment is of utmost importance, not only to advance the scientific knowledge about the experience of the body and neuropathic pain, but also fundamentally to promote efficacious pain management. Recent findings This review first discusses the mechanisms associated with phantom pain and summarizes the current treatments. The mechanisms underlying phantom pain primarily relate to peripheral/spinal dysfunction, and supraspinal and central plasticity in sensorimotor body representations. The most promising methods for managing phantom pain address the maladaptive changes at multiple levels of the neuraxis, for example, complementing pharmacological administration with physical, psychological or behavioural intervention. These supplementary techniques are even efficacious in isolation, perhaps by replacing the absent afferent signals from the amputated limb, thereby restoring disrupted bodily representations. Summary Ultimately, for optimal patient outcomes, treatments should be both symptom and mechanism targeted.

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.

A Randomized Controlled Trial of a Multifactorial Falls Prevention Intervention for Older Fallers Presenting to Emergency Departments

OBJECTIVES: To investigate the effect of a referral‐based targeted multifactorial falls prevention intervention on the occurrence of recurrent falls and injuries in older people presenting to an emergency department (ED) after a fall and discharged directly home from the ED.

The phantom in the mirror: A modified rubber-hand illusion in amputees and normals

The bodily boundaries in amputees may seem to be more malleable than in non-amputees, given the propensity for a phantom limb to embody a mirror-reflected hand. However, in the present investigation, in which phantom-limb illusions within body space are induced and manipulated, we found that perceiving phantom sensations and illusory embodiment does not require amputation. Surprisingly, in the present modified rubber-hand illusion, we found that simultaneous stroking or stimulation of the participants target hand was not necessary to induce illusions of embodiment and corresponding perceptual illusions. We tested this upper-limb paradigm in fourteen upper-limb amputees and twenty-six controls (including fourteen lower-limb amputees). We propose a model for embodiment of a rubber or real hand passively observed in a mirror. In this model, passive observation of the hand in the mirror triggers body representations (body image and body schema), most likely through activation of the posterior parietal cortex and temporo-parietal junction. Activity in these regions heightens awareness of peripersonal space and increases tactile sensitivity, and may subsequently enhance perception of illusory touch and embodiment. Furthermore, sense of embodiment may be more apparent to the participant when the hand is threatened; however, embodiment may even be strengthened when the motor system is engaged, evoking motor schemata to support the more easily induced perceptual embodiment via body image.

High incidence of ‘synaesthesia for pain’ in amputees

Synaesthesia for pain is a phenomenon where a person experiences pain when observing or imagining another in pain. Anecdotal reports of this type of experience have most commonly occurred in individuals who have lost a limb. Distinct from phantom pain, synaesthesia for pain is triggered specifically in response to pain in another. Here, we provide the first preliminary investigation into synaesthesia for pain in amputees to determine the incidence and characteristics of this intriguing phenomenon. Self-referring amputees (n=74) answered questions on synaesthesia for pain within a broader survey of phantom pain. Of the participants, 16.2% reported that observing or imagining pain in another person triggers their phantom pain. Further understanding of synaesthesia for pain may provide a greater insight to abnormal empathic function in clinical populations as well as therapeutic intervention for at risk groups.

Xenomelia: a social neuroscience view of altered bodily self-consciousness

Xenomelia, the “foreign limb syndrome,” is characterized by the non-acceptance of one or more of one’s own extremities and the resulting desire for elective limb amputation or paralysis. Formerly labeled “body integrity identity disorder” (BIID), the condition was originally considered a psychological or psychiatric disorder, but a brain-centered Zeitgeist and a rapidly growing interest in the neural underpinnings of bodily self-consciousness has shifted the focus toward dysfunctional central nervous system circuits. The present article outlays both mind-based and brain-based views highlighting their shortcomings. We propose that full insight into what should be conceived a “xenomelia spectrum disorder” will require interpretation of individual symptomatology in a social context. A proper social neuroscience of xenomelia respects the functional neuroanatomy of corporeal awareness, but also acknowledges the brain’s plasticity in response to an individual’s history, which is lived against a cultural background. This integrated view of xenomelia will promote the subfield of consciousness research concerned with the unity of body and self.

Meta-analytic evidence for decreased heart rate variability in chronic pain implicating parasympathetic nervous system dysregulation.

Abstract Both sympathetic and parasympathetic nervous systems are involved in regulating pain states. The activity of these systems seems to become disturbed in states of chronic pain. This disruption in autonomic balance can be measured through the assessment of heart rate variability (HRV), that is, the variability of the interval between consecutive heart beats. However, there is yet to be a systematic evaluation of the body of literature concerning HRV across several chronic pain conditions. Moreover, modern meta-analytical techniques have never been used to validate and consolidate the extent to which HRV may be decreased in chronic pain. Following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement guidelines, this study systematically evaluated and critically appraised the literature concerning HRV in people living with chronic pain. After screening 17,350 sources, 51 studies evaluating HRV in a chronic pain group met the inclusion criteria. Twenty-six moderate–high quality studies were included in quantitative meta-analyses. On average, the quality of studies was moderate. There were 6 frequency-domain and time-domain measures of HRV across a broad range of chronic pain conditions. High heterogeneity aside, pooled results from the meta-analyses reflected a consistent, moderate-to-large effect of decreased high-frequency HRV in chronic pain, implicating a decrease in parasympathetic activation. These effects were heavily influenced by fibromyalgia studies. Future research would benefit from wider use of standardised definitions of measurement, and also investigating the synergistic changes in pain state and HRV throughout the development and implementation of mechanism-based treatments for chronic pain.

Body Integrity Identity Disorder: Deranged Body Processing, Right Fronto-Parietal Dysfunction, and Phenomenological Experience of Body Incongruity

Body integrity identity disorder (BIID) is characterised by profound experience of incongruity between the biological and desired body structure. The condition manifests in “non-belonging” of body parts, and the subsequent desire to amputate, paralyse or disable a limb. Little is known about BIID; however, a neuropsychological model implicating right fronto-parietal and insular networks is emerging, with potential disruption to body representation. We argue that, as there is scant systematic research on BIID published to date and much of the research is methodologically weak, it is premature to assume that the only process underlying bodily experience that is compromised is body representation. The present review systematically investigates which aspects of neurological processing of the body, and sense of self, may be compromised in BIID. We argue that the disorder most likely reflects dysregulation in multiple levels of body processing. That is, the disunity between self and the body could arguably come about through congenital and/or developmental disruption of body representations, which, together with altered multisensory integration, may preclude the experience of self-attribution and embodiment of affected body parts. Ulimately, there is a need for official diagnostic criteria to facilitate epidemiological characterisation of BIID, and for further research to systematically investigate which aspects of body representation and processing are truly compromised in the disorder.

Synaesthesia for Pain: Feeling Pain with Another

In this chapter, we establish a theoretical framework for the rare manifestation of synaesthesia for pain; that is, the sensation in one part of the body (pain) produced by stimulus (pain) observed or imagined in another. We first describe mirror neuron systems (MNS) and the implications these systems have on imitation, behavioral mimicry, communication, socialization, and empathy. Behavioral and emotional contagion may signify disinhibition of behavioral mirroring that is closest to synaesthesia for pain. We describe cases of synaesthesia for pain, including one case of mirrored pain with hyperalgesia, eight cases of mirrored pain in a phantom limb following amputation, one case of mirrored pain in the stump following amputation, and one case of mirrored pain following traumatic childbirth. We then explore the mechanisms that may underlie the experience of pain when observing, or even thinking about, another in pain, including mirror neurons, empathy, and motor systems, the Autonomic Nervous System and visceral mechanisms, and the potential role of sensitization to pain and hypervigilance to pain cues. We conclude that synaesthesia for pain is most likely a consequence of disinhibited activation, or central sensitization, of a fundamentally adaptive system for the empathic perception of pain in another.

Oxytocin and the modulation of pain experience: Implications for chronic pain management

In an acute environment pain has potential protective benefits. However when pain becomes chronic this protective effect is lost and the pain becomes an encumbrance. Previously unheralded substances are being investigated in an attempt to alleviate the burden of living with chronic pain. Oxytocin, a neuropeptide hormone, is one prospective pharmacotherapeutic agent gaining popularity. Oxytocin has the potential to modulate the pain experience due to its ubiquitous involvement in central and peripheral psychological and physiological processes, and thus offers promise as a therapeutic agent. In this review, we discuss previous effective applications of oxytocin in pain-free clinical populations and its potential use in the modulation of pain experience. We also address the slowly growing body of literature investigating the administration of oxytocin in clinical and experimentally induced pain in order to investigate the potential mechanisms of its reported analgesic actions. We conclude that oxytocin offers a potential novel avenue for modulating the experience of pain, and that further research into this area is required to map its therapeutic benefit.