Training the "less-affected" forelimb after unilateral cortical infarcts interferes with functional recovery of the impaired forelimb in rats.

Purpose: Unilateral lesions of the sensorimotor cortex (SMC) in adult rats cause major behavioral changes in the ipsilesional, "less-affected" forelimb. An increase in function and reliance on this forelimb can aid compensation for contralesional impairments, but may also promote disuse and reduced functionality of the impaired forelimb. We hypothesized that training focused on the ipsilesional forelimb following a unilateral SMC lesion would reduce the efficacy of later motor rehabilitative training of the impaired forelimb. Methods: Rats with ischemic SMC lesions were trained on a skilled reaching task with the ipsilesional forelimb (PriorT) or received control procedures (Cont) for 10 days. Both groups were then trained with the impaired forelimb on the same reaching task for 10 days. Results: In comparison with Cont, PriorT rats had little improvement on the reaching task with the impaired forelimb and had a more enduring disuse of the impaired forelimb for postural support behaviors. Lesion sizes were similar between groups. Conclusions: Behavioral experience with the less-affected forelimb early after unilateral SMC lesions has the potential to increase disuse and dysfunction of the impaired forelimb, consistent with a training-induced exacerbation of learned non-use. These findings are suggestive of competitive processes in experience-dependent neural restructuring after brain damage.