Les habiletés spatio-cognitives des aveugles de naissance : résolution de labyrinthes tactiles
Navigation is predominately based on vision as it gathers spatial information simultaneously and allows a continuous update of our position relative to space. For many blind people who rely mainly on auditive, haptic, proprioceptive, olfactive and echolocating cues to navigate, leaving outside their home can be a challenge. Research on the navigational neural network in this particular population is therefore crucial to better adapt resources for visually impaired people and free them from isolation. Congenitally blind subjects are also an interesting population for the study of neuroplasticity. As their brain was built without any visual input, most structures related to vision are reduced in volume compared to those of seeing subjects. Moreover, their occipital cortex, a region normally dedicated to vision, has a suprametabolic activity at rest, which could represent a virgin territory that can be recruited by other modalities to accomplish various sensory tasks. Recently some researchers have demonstrated the involvement of this region in sensory tasks such as tactile discrimination and auditive localisation. Other intramodal plastic changes have also been observed in the blind’s navigational neural network. The posterior part of hippocampus, involved in cognitive mapping, is reduced in volume while the anterior section is enlarged in blind subjects. Although some anatomical plastic changes have been observed in congenitally blind’s brain navigational system, their functional aspect remains to be elucidated. The purpose of this study was to investigate the neural correlates of navigation in congenital blindness and to link them with the blinds’ spatio-cognitive skills. The first behavioral study identified route learning difficulties in congenitally blind participants when they were ask to navigate inside small-scaled tactile mazes. Using functional magnetic resonance imagery in the second study, these problems were associated with the recruitment of brain regions involved in an egocentric perspective processing, such as right superior parietal lobule. While blindfolded seeing subjects excelled in the maze task, they recruited structures involved in allocentric processing, such as hippocampus and parahippocampus. Moreover, the second study confirmed the recruitment of occipital cortex in a navigation task for blind subjects only. This strengthens the involvement of crossmodal plasticity in higher level cognitive tasks, such as navigation.
navigation navigation hippocampus blindness maze haptic functional imaging