How does the human brain deal with a spinal cord injury?

The primary sensorimotor cortex of the adult brain is capable of significant reorganization of topographic maps after deafferentation and de-efferentation. Here we show that patients with spinal cord injury exhibit extensive changes in the activation of cortical and subcortical brain areas during hand movements, irrespective of normal (paraplegic) or impaired (tetraplegic patients) hand function. Positron emission tomography ([15O]-H2O-PET) revealed not only an expansion of the cortical 'hand area' towards the cortical 'leg area', but also an enhanced bilateral activation of the thalamus and cerebellum. The areas of the brain which were activated were qualitatively the same in both paraplegic and tetraplegic patients, but differed quantitatively as a function of the level of their spinal cord injury. We postulate that the changes in brain activation following spinal cord injury may reflect an adaptation of hand movement to a new body reference scheme secondary to a reduced and altered spino-thalamic and spino-cerebellar input.