Abstract
Transection of the median nerve typically causes lifelong restriction of fine sensory and motor skills of the affected hand despite the best available surgical treatment. Inspired by recent findings on activity-dependent structural plasticity of the adult brain, we used voxel-based morphometry to analyze the brains of 16 right-handed adults who more than two years earlier had suffered injury to the left or right median nerve followed by microsurgical repair. Healthy individuals served as matched controls. Irrespective of side of injury, we observed gray matter reductions in left ventral and right dorsal premotor cortex, and white matter reductions in commissural pathways interconnecting those motor areas. Only left-side injured participants showed gray matter reduction in the hand area of the contralesional primary motor cortex. We interpret these effects as structural manifestations of reduced neural processing linked to restrictions in the diversity of the natural manual dexterity repertoire. Furthermore, irrespective of side of injury, we observed gray matter increases bilaterally in a motion-processing visual area. We interpret this finding as a consequence of increased neural processing linked to greater dependence on vision for control of manual dexterity after median nerve injury because of a compromised somatosensory innervation of the affected hand.
Highlights
Despite the best available surgical repair, an injury transecting the median nerve typically causes lifelong disability characterized by loss of fine sensory and motor hand functions because of an inadequate reinnervation of the hand[1,2,3,4]
Our findings indicate that median nerve transection followed by surgical repair and reinnervation of the hand can cause long-term structural changes in several brain areas, and in particular those that are functionally implicated in planning and control of skilled manual actions
That the detected effects were synaptically remote from the lesioned neurons and involved reductions as well as increases of cortical gray matter volume strongly suggest that they represent complex activity-dependent adaptations in specific processing units in the brain[11,12,47,48]
Summary
Despite the best available surgical repair, an injury transecting the median nerve typically causes lifelong disability characterized by loss of fine sensory and motor hand functions because of an inadequate reinnervation of the hand[1,2,3,4]. Inspired by recent findings on activity-dependent structural plasticity in the adult brain[11,12], we asked whether the imperfect reinnervation and the resulting deterioration in fine dexterity after repaired median nerve injuries can drive structural changes in the brain. We expected that activity-dependent structural changes might occur in the hand area of the primary sensorimotor cortex contralateral to the injured side since experimental peripheral nerve lesions in animals can cause substantial functional reorganizations both in contralesional primary somatosensory area (S1)[24,25,26,27] and primary www.nature.com/scientificreports/.
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