Structural changes in hand related cortical areas after median nerve injury and repair.

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.