Why Brain Science is Essential to the Success of Hand Allotransplantation

The capacity of the brain to reorganize in response to changes in stimulation plays a critical, yet poorly understood, role in the successful outcome of allogeneic hand transplants. Here, I begin by reviewing evidence on intra and interhemispheric changes in functional organizations that follow upper extremity amputation. The absence of data prior to limb loss makes it impossible to determine whether these changes are fully reversed following hand transplantation. However, accumulating data suggest that areas of the sensory and motor cortex that likely were devoted to representing the hand prior to amputation do come to represent the transplanted hand, even after years or decades of complete loss of afferent and efferent communication. Nevertheless, at least some amputation-related cortical changes may persist even long after a transplant. These results are consistent with a model in which restoration of afferent and efferent signals between hand and brain enables gross recovery of cortical organization through reactivation of existing networks. However, recovery of finer-grained details of the cortical maps requires experience-dependent changes, due to peripheral reinnervation errors and lower-level structural reorganization, recovering finer-grained details of cortical maps requires experience-dependent changes. These latter changes evolve slowly, are essential to achieve optimal sensory and motor functions, and stand to benefit from advances in evidence-based neurorehabilitation.