Somatosensory Mapping of Human Cortex with Visual Deprivation

Topographic mapping between the functionally specialized cortical brain areas and the sensory input is a fundamental principle of neural processing. Functional magnetic resonance imaging (fMRI) has noninvasively revealed such topographic maps in visual, somatosensory, and parietal cortices in humans. In addition, it is known that multisensory brain areas exist (area VIP in parietal lobe) receiving input from both sensory modalities: vision and touch. However, although visual and somatotopic maps are well established with intact vision, very little is known about the topographic maps in early or late blindness condition. This work investigated somatotopic maps in VIP area, occipital areas and parietal areas in four blind patients: two congenital blind and two late blind. Their activated areas were compared to visual maps and somatotopic maps found in one sighted participant. fMRI and established visual and somatotopic stimuli were used. During somatotopic mapping in blind and in the sighted participant the face was stimulated with gentle air puffs. During visual mapping which was applied in the sighted participant, high-contrast checkerboard stimuli were presented during attentional task. Statistical data analysis was performed with standardised analysis package, the FreeSurfer.08. As expected, in the sighted participant visual maps were localised in the occipital lobe and in the VIP area, while somatotopic maps were found in the somatosensory cortex located in the parietal lobe. In the sighted person the VIP area coded the location of visual stimuli with respect to the retina (upper or lower field of visual space) and equally presented the somatotopic stimulation with respect to the upper or lower part of the face. In blind participants activations in occipital visual areas, parietal areas and VIP area were found. Relevant differences were not found between Early and Late Blind in VIP and parietal areas activation. Face representation of VIP and also of parietal areas in both groups of blind were more scattered and unexpectedly less prominent than in sighted participant. Activations in occipital and medio-occipital areas in late blind individuals support the fact that they still use their visual cortices years later for a kind of visual imagery, given the known dependence of the visual system on early visual experience. Activations in occipital regions in early blind could suggest that occipital areas are activated as somatosensory areas, as in late blind. Connectivity between somatosensory cortices and visual cortices may be strengthened with both types of visual deprivation.