Compensatory changes at the cerebral cortical level after spinal cord injury.

Neurorehabilitation is based on the concept that rehabilitative training recruits neuronal systems that remain intact after the brain and/or spinal cord injury to take over the impaired function. Understanding the neural mechanism of recovery will surely contribute to the development of evidence-based rehabilitation therapies. Recent studies have shown that after a lesion of the lateral corticospinal tract at midcervical segments, the remaining pathways can compensate for finger dexterity in macaque monkeys in a few weeks to months. Combined brain imaging and reversible pharmacological inactivation of motor cortical regions suggested that the recovery involves the bilateral primary motor cortex during the early recovery stage and more extensive regions of the contralesional primary motor cortex and bilateral premotor cortex during the late stage. Thus, contribution of each cortical region changes depending on the recovery stage, suggesting that the brain uses available pre-existing neural systems by reducing inhibition during the early stage and enhances the original systems or recruits other systems by plastic change of the neural circuits during the late stage. These changes in the activation pattern of motor-related areas represent an adaptive strategy for functional compensation after spinal cord injury.