RESUMO
The observation and evaluation of other's pain activate part of the neuronal network involved in the actual experience of pain, including those regions subserving the sensori-discriminative dimension of pain. This was largely interpreted as evidence showing that part of the painful experience can be shared vicariously. Here, we investigated the effect of the visual perspective from which other people's pain is seen on the cortical response to continuous 25 Hz non-painful somatosensory stimulation (somatosensory steady-state response: SSSR). Based on the shared representation framework, we expected first-person visual perspective (1PP) to yield more changes in cortical activity than third-person visual perspective (3PP) during pain observation. Twenty healthy adults were instructed to rate a series of pseudo-dynamic pictures depicting hands in either painful or non-painful scenarios, presented either in 1PP (0-45° angle) or 3PP (180° angle), while changes in brain activity was measured with a 128-electode EEG system. The ratings demonstrated that the same scenarios were rated on average as more painful when observed from the 1PP than from the 3PP. As expected from previous works, the SSSR response was decreased after stimulus onset over the left caudal part of the parieto-central cortex, contralateral to the stimulation side. Moreover, the difference between the SSSR was of greater amplitude when the painful situations were presented from the 1PP compared to the 3PP. Together, these results suggest that a visuospatial congruence between the viewer and the observed scenarios is associated with both a higher subjective evaluation of pain and an increased modulation in the somatosensory representation of observed pain. These findings are discussed with regards to the potential role of visual perspective in pain communication and empathy.
RESUMO
UNLABELLED: The observation of pain in other individuals is known to impact the cerebral activity in regions dedicated to one's nociception, as well as the behavior toward the person in pain. However, it remains unclear whether this shared representation for pain modulates somatosensory processing to nonpainful stimuli and whether this modulation is limb specific. Twenty right-handed healthy participants viewed a series of pictures depicting right hands or right feet in painful or nonpainful situations while light repetitive (25 Hz) mechanical stimuli were applied to the hand. The cortical excitability to these nonpainful stimuli was measured through the energy in the 25-Hz frequency band of electroencephalographic data. Following picture onset, a combination of nonspecific and specific modulation of cortical excitability was found. The former was widespread over the parieto-central region and likely related to factors such as attention. The latter was mostly restricted to 3 electrodes over the parietal cortex contralateral to the stimulation of the hand, and was specifically associated with the observation of others' hand in painful scenarios. This result confirms that the observation of pain can modulate somatosensory cortical excitability in an effector-specific way. The findings add to the accumulating evidence that other people's somatic pain is mapped onto the observer's sensori-motor system and offers a new paradigm to investigate potential neurophysiological changes in care providers who are often overexposed to others' pain. PERSPECTIVE: This electroencephalography study demonstrates with a quick, easily implementable, and noninvasive paradigm that the change in cortical somatosensory excitability during pain observation is limb-specific, and confirms from a neuroscience perspective that being exposed to others' pain implies more than the sharing of an affective experience.