Neural correlates of distorted body representations underlying tactile distance perception

Introduction: The ability to localize touch on the body, and in particular tactile distance perception, has been largely used as a tool to investigate how the somatosensory system contributes to body representations. Nevertheless, there is little evidence about the neural basis of this phenomena. Recent studies found that on the perceptual level, tactile configurations, at least in the case of the hand, are highly distorted with the hand dorsum represented as wider and squatter than it actually is. Here, we aim to define the neural basis of this phenomena.

Methods: 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 an 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 interest, we computed the pairwise Euclidean distances between the neural patterns associated with the tactile stimulations and we then compared the neural dissimilarity matrices to the model obtained from the behavioral study.

Results: 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 SI.

Discussion: This suggests that SI, rather than higher level brain areas, is critical to process tactile distance perception.