Isolated focal dystonias (IFDs) are phenomenologically characterized by abnormal movements and/or postures.1 Although overt sensory deficits are absent, abnormalities in somatosensory processing have been documented in various types of IFDs not only in dystonic, but also in nonaffected body parts (reviewed in reference 2). While changes in temporal somatosensory processing in IFDs are well documented with an array of different assessment tools,2, 3 the role of spatial somatosensory findings remains less well understood.

Already in 1834, Weber observed that the perceived distance between 2 tactile stimuli relates systematically to tactile sensitivity, a finding that was later associated with cortical receptive field (RF) size.4 RFs for body regions with hairy skin are usually oval shaped.5, 6 This asymmetric structure leads to varying size estimations depending on stimulus orientation: tactile distances are perceived as larger in the mediolateral than in the proximodistal body axis, an effect called anisotropy. Recently, a paradigm has been developed that allows testing of tactile spatial perception across 8 orientations to provide a more accurate estimation of RF size, shape, and orientation.7 Indeed, perceptual distortions of tactile space match cortical tactile space organization in the primary somatosensory cortex.

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