Neurologic deficits after neonatal brain lesions are often less debilitating than after comparable lesions in the adult. As a possible explanation for this phenomenon, numerous experiments have demonstrated neuroanatomical remodeling in response to brain lesions in the newborn. This proposal is designed to examine possible correlations between recovery and plasticity using the rodent motor system. Studies will include a comparison of limb preference after neonatal and adult pyramidotomy in search of behavioral differences that may correlate with the aberrant ipsilateral corticospinal tract that develops after neonatal pyramidotomy. Anatomical studies employing several histological techniques including the Fink-Heimer method, the horseradish peroxidase method and autoradiography are designed to examine the afferent and efferent connections of the red nucleus as well as corticopontine and cortico-olivary connections. Further studies will examine these connections for alterations that may occur in response to neonatal cerebral and cerebellar lesions. In addition to functional correlations, these stdies are designed to explore basic mechanisms involved in central nervous system reorganization.