Somatotopic specificity of perceptual and neurophysiological changes associated with visuo-proprioceptive realignment

Spatial realignment of visual and proprioceptive estimates of hand position can occur in response to a perturbation. E.g., viewing the hand underwater while washing dishes. This form of multisensory perceptual learning presumably affects perceived hand position, which is used in movement planning. Consistent with this idea, we recently observed changes in motor cortex (M1) index finger representation associated with visuo-proprioceptive misalignment at that fingertip ([Munoz-Rubke et al., 2017][1]). In three experiments with healthy human participants, we asked whether these changes are specific to the brain’s representation of the misaligned finger (somatotopically focal), or whether they extend to other parts of the hand and arm that would be needed to move the misaligned finger (somatotopically broad). In Experiments 1 and 2, participants experienced misaligned or veridical visuo-proprioceptive information about the index fingertip. Before and after the perceptual alignment task, we used transcranial magnetic stimulation (TMS) to assess M1 representation of five hand and arm muscles. The index finger representation showed the expected association between M1 excitability and visuo-proprioceptive realignment, as did the pinkie finger representation to a lesser extent. Forearm flexors, forearm extensors, and biceps did not show any such relationship. In Experiment 3, we asked subjects to indicate their proprioceptive estimate of the fingertip, knuckle, wrist, and elbow, before and after misalignment at the fingertip. Proprioceptive realignment at the knuckle, but not the wrist or elbow, was correlated with realignment at the fingertip. These results suggest the effects of perceptual perturbation are somatotopically focal in both sensory and motor domains. Significance Statement Multisensory and motor processing have largely been examined separately, limiting our understanding of how these systems interact. Motor adaptation is thought to affect somatosensory perception and neurophysiology, but the reverse interaction, an effect of perceptual learning on the motor system, has rarely been considered. Here we examine the effect of a somatotopically localized visuo-proprioceptive perturbation on motor neurophysiology and conscious perception. We found somatotopically-focal effects in both domains. This correspondence highlights the tight relationship between sensory and motor systems, but also raises the possibility that perceptual learning may not generalize to other body parts as motor learning does. Rather, it appears to create a localized distortion in the multisensory body representation, with correspondingly local changes in the motor cortex representation. ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-34