Consequences of forced disuse of the impaired forelimb after unilateral cortical injury.

Extreme over-reliance on the impaired forelimb following unilateral lesions of the forelimb representation area of the rat sensorimotor cortex (FL-SMC) leads to exaggeration of injury when overuse is begun during the first week, but not later periods, after injury. Behavioral impairment is partially worsened by the additional tissue loss. In the present study, we show that complete disuse of the impaired forelimb during the first post-operative week renders surviving tissue vulnerable to later overuse of the same limb, in effect extending the window of vulnerability in which use-dependent exaggeration of brain injury can occur. Behavioral recovery is disrupted by complete disuse, but the degree of impairment is variable depending on the nature of the behavioral test employed. Our results uphold the idea that mild rehabilitative training early after injury is beneficial, while either extreme overuse or complete disuse may disrupt functional recovery.