Neurotransmitters and motor activity: effects on functional recovery after brain injury.

There are complex relationships among behavioral experience, brain morphology, and functional recovery of an animal before and after brain injury. A large series of experimental studies have shown that exogenous manipulation of central neurotransmitter levels can directly affect plastic changes in the brain and can modulate the effects of experience and training. These complex relationships provide a formidable challenge for studies aimed at understanding neurotransmitter effects on the recovery process. Experiments delineating norepinephrine-modulated locomotor recovery after injury to the cerebral cortex illustrate the close relationships among neurotransmitter levels, brain plasticity, and behavioral recovery. Understanding the neurobiological processes underlying recovery, and how they might be manipulated, may lead to novel strategies for improving recovery from stroke-related gait impairment in humans.