Research on empathy for pain has provided evidence of an empathic bias toward racial ingroup members. In this study, we used for the first time the “minimal group paradigm” in which participants were assigned to artificial groups and required to perform pain judgments of pictures of hands and feet in painful or non-painful situations from self, ingroup, and outgroup perspectives. Findings showed that the mere categorization of people into two distinct arbitrary social groups appears to be sufficient to elicit an ingroup bias in empathy for pain.

Background: Emotional context may play a crucial role in movement production. According to simulation theories, emotional states affect motor systems. The aim of this study was to compare postural responses assessed by posturography and electromyography when subjects were instructed to imagine themselves in a painful or a non-painful situation.Methods: Twenty-nine subjects (22.3 ± 3.7 years) participated in this study. While standing quietly on a posturographic platform, they were instructed to imagine themselves in a painful or non-painful situation. Displacement of the center of pressure (COP), leg muscle electromyographic activity, heart rate, and electrodermal activity were assessed in response to painful and non-painful situations.Results: The anteroposterior path was shorter (p < 0.05) when subjects imagined themselves in a painful situation (M = 148.0 ± 33.4 mm) compared to a non-painful situation (158.2 ± 38.7 mm). Higher tibialis anterior (TA) activity (RMS-TA = 3.38 ± 1.95% vs. 3.24 ± 1.85%; p < 0.001) and higher variability of soleus (SO) activity (variation coefficient of RMS-SO = 13.5 ± 16.2% vs. M = 9.0 ± 7.2%; p < 0.05) were also observed in painful compared to non-painful situations. No significant changes were observed for other physiological data.Conclusion: This study demonstrates that simulation of painful situations induces changes in postural control and leg muscle activation compared to non-painful situations, as increased stiffness was demonstrated in response to aversive pictures in accordance with previous results.

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Embodiment is made possible by the ability to imagine ourselves in a particular situation (mental simulation). Postural changes have been demonstrated in response to painful situations, but the effect of an implicit instruction has not been studied. The present study was designed to record differential responses according to whether or not subjects were instructed to imagine themselves in a painful or non-painful situation. Painful stimuli and instructions to mentally simulate the displayed situation were hypothesized to induce postural changes that could be demonstrated by changes in the center of pressure (COP) trajectory compared to viewing the same stimuli with no instructions. We hypothesized that mental simulation of a painful situation would induce embodiment of the emotional situation as reflected by posterior displacement of the COP and physiological responses as compared to passive observation of the same visual scene. Thirty-one subjects participated in this study while standing quietly on a posturographic platform with presentation of visual stimuli depicting scenes defining three experimental conditions (painful, non-painful and neutral situations) for 12 s. Physiological measurements [heart rate (HR) and electrodermal activity] and postural responses (COP displacements) were recorded in response to the stimuli with or without instructions to imagine themselves in the situation. Time-course analyses (1 s sliding window) were conducted for several postural parameters, HR and electrodermal response. An interaction effect (instruction × stimuli × time) demonstrated that mental simulation induced posterior displacement of the mean position of the COP at different times during presentation of visual stimuli (4 s; 9–12 s). An effect of instruction was reported for HR (HR was higher in the mental simulation condition), while a stimulation effect was reported only for HR (lower for painful stimuli than for non-painful stimuli). The results of time-course analyses demonstrated embodiment of painful situations by postural control modulations and physiological changes depending on whether or not the participants were instructed to imagine themselves in the situation.

BACKGROUND: Information on altered foot pressures during ambulation would clarify how far limb deformities modify walking patterns in cerebral palsy (CP), and whether such data can inform prognosis and guide rehabilitation. OBJECTIVE: To compare patterns of plantar pressures during walking between children with CP and their able-bodied (AB) peers. METHODS: Twenty-five children/adolescents (10 with hemiplegia, 5 with diplegia, and 10 AB, respective ages 13.0 ± 1.9, 13.0 ± 0.6 and 14.0 ± 0.7 years) walked a 12 m line at a self-selected speed. Spatio-temporal parameters and peak in-shoe plantar pressures were recorded for both feet, using the Parotec analysis system. RESULTS: Walking speeds (m·s −1 ) differed significantly between groups (0.65 ± 0.13, hemiplegia, 0.93 ± 0.22 diplegia and 1.26 ± 0.05 AB), with shorter stride lengths in CP. Contact time, double support time and step duration were also shorter in hemiplegia. Plantar pressures differed substantially and consistently between AB and CP, with increased medial heel pressures in hemiplegia, and reduced hallux and lateral heel pressures but increased lateral, medial mid-foot and first metatarsal pressures in diplegia. CONCLUSIONS: Substantial alterations in spatio-temporal parameters (greater in hemiplegia than in diplegia) and plantar pressure distribution reflect attempts to compensate for poor stability of posture in CP. Further study of these adaptive changes holds clinical promise in providing data relevant to the design of orthotics, determinations of prognosis and the planning of neurorehabilitation.