Neonatal frontal lesion in unilateral hemisphere enhances the development of the intact higher motor cortex in the rat

The influence of the neonatal frontal lesion in unilateral cerebral hemisphere for the organization of intact forelimb motor cortex in the rat was investigated by intracortical microstimulation (ICMS). The relative size of the rostral forelimb area (RFL) compared to the caudal forelimb area (CFL) in the ipsilateral motor field of lesioned rat was significantly greater than those of contralateral in normal and lesioned rats. The optimal sites of the stimulation for ipsilateral responses in lesioned rats were located in the RFL, while the optimal sites for contralateral were located caudolaterally, as for those of normal rats. At the ipsilateral optimal sites within the RFL in the lesioned animals, the threshold for the ipsilateral responses was lower than that for the contralateral responses. That is, the intact hemisphere of the animal preferentially developed the RFL rather than the CFL, for the ipsilateral forelimb. This may suggest a critical role for the RFL in individual forelimb motor control within the normal hemisphere. (C) 2003 Elsevier Science B.V. All rights reserved.