Neural correlates of distorted body representations underlying tactile distance perception

The ability to localize touch on the body has been largely used as a tool to investigate how the somatosensory system contributes to body representations. Recent studies found that at perceptual level, tactile configurations at least in the case of the hand are highly distorted (Longo, 2017). Here, we aim to define the neural basis of this phenomenon. In a behavioral experiment, participants estimated the distance between touches delivered on the hand dorsum. Using multidimensional scaling we reconstructed a perceptual map of the skin space. Analysis of spatial distortion showed that the skin space was stretched in the mediolateral hand axis. To determine the neural correlates of these body distortions, we performed a functional magnetic resonance (fMRI) study in which we delivered nine tactile stimuli, organized as a 3 x 3 square grid, on the dorsum of the right hand. Within pre-defined regions of interests we computed the pairwise Euclidean distances between the neural patterns associated with the tactile stimulations and we compared the neural dissimilarity matrices to the model obtained from the behavioral study. We were able to reconstruct the shape of the skin space in the contralateral primary somatosensory (SI) and motor cortices, with a distorted profile that emerged only in the SI. This suggests that these areas are critical to generate the tactile representations of the dorsum of the hand.