Cortical Plasticity and Recovery from Brain Injury

Ramanathan et al have made some interesting observations on the recovery of complex movement patterns after focal damage to the rat motor cortex. They used "behaviorally relevant," long-duration (500-msec) intracortical microstimulation of rat motor cortex that causes complex, multijoint movements. A consistent topographic distribution of these complex motor patterns is present across the motor cortex in naïve rats. They documented the plasticity of these complex movement patterns after focal cortical injury by measuring a significant expansion of specific complex movement representations in response to rehabilitative training after injury. (The rehabilitative training task required animals to use the forepaw to reach through a small slit in a Plexiglas chamber and grasp and retrieve a small food pellet positioned on a platform near the chamber.) The degree of functional recovery attained after cortical injury and rehabilitation correlated significantly with a specific feature of map reorganization, the ability to reexpress movement patterns disrupted by the initial injury. This suggests the existence of complex movement representations in the rat motor cortex that exhibit plasticity after injury and rehabilitation. Thus there is a significant correlation between the reorganization of disrupted complex representations and behavioral recovery after brain injury.

The graphic shows the types of complex movement elicited by long-duration microstimulation. The maps of motor cortex regulating these movements are a bit complex to show in this posting.

Figure: Complex movements elicited by long-duration microstimulation. (A–C) Three types of complex movements evoked by long-duration stimulation within motor cortex. Complex movements elicited by long-duration microstimulation occur across multiple joints. (A) Reaching movement characterized by rostral displacement of the elbow and shoulder, without change in wrist configuration. (B) Retraction characterized by caudal displacement of the elbow and forepaw. (C) Grasping movement characterized by contraction of all digit joints simultaneously. Credit: PNAS.