Psychophysical experiments have demonstrated large and highly systematic perceptual distortions of tactile space. Such a space can be referred to our experience of the spatial organisation of objects, at representational level, through touch, in analogy with the familiar concept of visual space. We investigated the neural basis of tactile space by analysing activity patterns induced by tactile stimulation of nine points on a 3 × 3 square grid on the hand dorsum using functional magnetic resonance imaging. We used a searchlight (...) approach within pre-defined regions of interests to compute the pairwise Euclidean distances between the activity patterns elicited by tactile stimulation. Then, we used multidimensional scaling to reconstruct tactile space at the neural level and compare it with skin space at the perceptual level. Our reconstructions of the shape of skin space in contralateral primary somatosensory and motor cortices reveal that it is distorted in a way that matches the perceptual shape of skin space. This suggests that early sensorimotor areas critically contribute to the distorted internal representation of tactile space on the hand dorsum. (shrink)

Tactile distance perception is believed to require that immediate afferent signals be referenced to a stored representation of body size and shape (the body model). For this ability, recent studies have reported that the stored body representations involved are highly distorted, at least in the case of the hand, with the hand dorsum represented as wider and squatter than it actually is. Here, we aim to define the neural basis of this phenomenon. In a behavioural experiment participants estimated the distance (...) between touches on two points by adjusting the length of a visually-presented line on the screen. The technique of multidensional scaling (MDS) was used to reconstruct a perceptual map of tactile space. Analysis of spatial distortion using Procrustes alignment showed that maps were stretched in the mediolateral hand axis. In order to determine the neural correlates of these body distortions, we performed an fMRI study. For each participant, we used a searchlight pattern classifier with Euclidean distance on pre-defined regions of interests (ROIs). In order to relate the representations between the different points and to computational models, we compare response-pattern dissimilarity matrices in these ROIs. Similar to the behavioural experiment, we used MDS to reconstruct maps of the neural representation of tactile space using the values from the dissimilarities matrices. We were able to reconstruct the perceptual map of tactile space in the contralateral primary somatosensory and motor cortices. This suggests that these areas are critical to generate the tactile representations of the dorsum of the hand. (shrink)

We examined the neural basis of tactile distance perception by analyzing activity patterns induced by tactile stimulation of nine points on a 3 x 3 square grid on the hand dorsum using functional magnetic resonance (fMRI). We used a searchlight approach within pre-defined regions of interests (ROIs) to compute the pairwise Euclidean distances between the activity patterns elicited by tactile stimulation. Then, we used multidimensional scaling (MDS) to reconstruct skin space at the neural level and compare it with skin space (...) at the perceptual level. Our reconstructions of the shape of skin space in contralateral primary somatosensory (SI) and motor (M1) cortices reveal that it is distorted in a way that matches the perceptual shape of skin space. This suggests that early sensorimotor areas are critical to processing tactile distance perception. (shrink)