Cortical KCl reinstates forelimb placing following damage to the internal capsule

Following unilateral damage to the internal capsule, rats failed to use the contralateral forelimb during tests of contact, chin, and visual placing reactions. Infusion of potassium chloride onto the sensorimotor cortex contralateral to the lesion reinstated placing in the impaired limb and abolished placing in the normal limb. As the drug dissipated, placing in the impaired limb gradually deteriorated, while placing in the normal limb returned. In contrast, potassium chloride applied to the ipsilateral cortex did not reinstate placing. These findings suggest that the loss of forelimb placing following lesions of the internal capsule is due, at least in part, to tonic inhibition from the cortex contralateral to the lesion.