Enhanced corticospinal response to observed pain in pain synesthetes

Abstract

Observing noxious injury to another's hand is known to induce corticospinal inhibition that can be measured in the observer's corresponding muscle. Here, we investigated whether acquired pain synesthetes, individuals who experience actual pain when observing injury to another, demonstrate less corticospinal inhibition than do controls during pain observation, as a potential mechanism for the experience of vicarious pain. We recorded motor-evoked potentials (MEPs) induced at two time points through transcranial magnetic stimulation while participants observed videos of a hand at rest, a hypodermic needle penetrating the skin, a Q-tip touching the skin, and a hypodermic needle penetrating an apple. We compared MEPs in three groups: 7 amputees who experience pain synesthesia, 11 nonsynesthete amputees who experience phantom limb pain, and 10 healthy controls. Results indicated that the pain synesthete group demonstrated significantly enhanced MEP response to the needle penetrating the hand, relative to the needle not having yet penetrated the hand, as compared with controls. This effect was not observed exclusively in the same muscle where noxious stimulation was applied. We speculate that our findings reflect a generalized response to pain observation arising from hyperactivity of motor mirror neurons not involved in direct one-to-one simulation but, rather, in the representation of another's experience.

Fibromyalgia patients and controls are equally accurate in detecting tactile stimuli while observing another in pain: an experimental study

“…For example, those who experience vicarious pain (that is, an actual somatosensory experience in response to the observation of pain) show a hyperactivity of motor mirror neurons (enhanced motor-evoked potentials) to the observation of a needle penetrating the hand, relative to the needle having not yet penetrated the hand, as compared with controls (Fitzgibbon, Enticott, Bradshaw, Giummarra, Chou, Georgiou-Karistianis, & Fitzgerald, 2012a). These observations are intriguing as they indicate that tactile or nociceptive input may not be necessary to experience touch or pain.…”

Vicarious pain while observing another in pain: an experimental approach

“…Only little research is available on the conditions in which vicarious pain occurs and on the underlying mechanisms. Especially the role of empathy or processes underlying empathy have predominantly been investigated (e.g., Fitzgibbon et al, 2012a,b). …”

“…In another study with 74 phantom limb patients (Fitzgibbon et al, 2010a), 16% of the participants reported that observing or imagining pain in another person triggers their phantom pain. There is little research yet available on the occurrence of vicarious pain and underlying mechanisms (but see Fitzgibbon et al, 2012a,b). Most evidence stems from clinical studies, using self-report questionnaires, describing the phenomenon and research in amputees.…”

Power changes how the brain responds to others.

“…Tremblay, Í& Théoret, 2010). Lastly, akin to several studies in the literature, stimulator output was lowered to determine the minimum intensity capable of eliciting visible MEPs (~1 mV peak to peak) on more than 50% of TMS pulses, which was used as the protocol intensity rather than stimulating at 110%-120% of resting motor threshold (Enticott et al, 2012;Hogeveen & Obhi, 2012;Lepage et al, 2010). Stimulation intensity ranged from 49% to 75% (M = 61%) of stimulator output.…”