Monkey models of recovery of voluntary hand movement after spinal cord and dorsal root injury

The hand is unique to the primate and manual dexterity is at its finest in the human (Napier 1980), so it is not surprising that cervical spinal injuries that even partially block senso-rimotor innervation of the hand are frequently debilitating (Anderson 2004). Despite the clinical need to understand the neuronal bases of hand function recovery after spinal and/or nerve injuries, relatively few groups have systemati-cally related subtle changes in voluntary hand use following injury to neuronal mechanisms in the monkey. Human and macaque hand anatomy and function are strikingly similar, which makes the macaque the favored nonhuman primate model for the study of postinjury dexterity. In this review of monkey models of cervical spinal injury that have success-fully related voluntary hand use to neuronal responses dur-ing the early postinjury months, the focus is on the dorsal rhizotomy (or dorsal rootlet lesion) model developed and used in our laboratory over the last several years. The re-view also describes macaque monkey models of injuries to the more central cervical spine (e.g., hemisection, dorsal column) that illustrate methods to assess postlesion hand function and that relate it to neurophysiological and neuro-anatomical changes. Such models are particularly important for understanding what the sensorimotor pathways are ca-pable of, and for assessing the outcome of therapeutic in-terventions as they are developed. Key Words: cervical spinal cord; dexterity; dorsal rhi-zotomy; dorsal root lesion; hand function; monkey; neuro-nal plasticity; nonhuman primate; precision grip; sensorimotor functio