Danger in the dark! Localization of nociceptive stimuli in normally sighted and congenitally blind people

Aim of investigation: In order to adapt our behavior and defend our body against threatening stimuli that might potentially inflict damages to the body, it is crucial to identify which part of the body is being damaged, and also to locate the threatening stimulus in its surroundings. Therefore, the brain has to coordinate the representation of the body with that of external space. To this aim, somatosensory inputs have to be remapped from a somatotopic representation (“which limb is stimulated?”) towards a spatiotopic representation (“where is the stimulated limb in external space?”). This somatosensory remapping is thought to be mainly shaped by our visual experiences during early development. Here, we investigated the role of visual experience in shaping the spatial perception of nociceptive inputs by comparing the ability of normally sighted to localize nociceptive stimuli with that of congenitally blind individuals, that is, people who have never had visual experience. Method: Congenitally blind and blindfolded sighted participants performed a temporal order judgment task in which they had to discriminate the temporal order of two consecutive CO₂-laser heat nociceptive stimuli applied on each hand. The task was performed with the hands either uncrossed or crossed over body midline. This latter posture was used to introduce a conflict between the somatotopic and spatiotopic representations (e.g. “my left hand lays in the right side of space”). Results: While congenitally blinds were not affected by the posture, the performance of the sighted people decreased in the crossed as compared to the uncrossed condition. This indicates that nociceptive stimuli are automatically remapped into a spatiotopic representation that can interfere with the somatotopic representation. On the contrary, congenitally blinds’ performance seems to only rely on a somatotopic map. Conclusions : Together, these results suggest that the way we perceive nociceptive stimuli is shaped by visual experience during cortical maturation