A study of XXXX evoked by intracortical microstimulation after hemicerebellectomy in newborn, young and adult @entity35 .

@entity75 @entity910 @entity76 @entity35 @entity717
Microstimulation of the cerebral motor cortex in normal adult @entity35 evokes low-threshold contralateral and high-threshold @entity910 . The present study examined the effects of hemicerebellar ablation at different postnatal ages on the current threshold values needed to evoke @entity717 by intracortical stimulation. Animals that @entity75 at various ages were electrophysiologically tested 4-6 months postoperatively. In all groups, including non-lesion control animals, @entity717 contralateral to the stimulating electrode were evoked at threshold values of 7-11 microA. Ipsilateral @entity717 for control animals as well as those @entity76 at 45 or 120 days of age showed significantly higher mean threshold current values, ranging from 38 to 45 microA. In contrast, the mean threshold current values for @entity910 in adult animals sustaining @entity75 at 2, 10 or 21 days of age were significantly lowered, ranging from 16 to 22 microA. Secondary lesions of spared cerebellar tissue or callosal fibers in adult animals that had sustained hemicerebellectomy at two days of age had no effect on the current intensities needed to evoke forelimb responses. In comparison, lesions of the cerebral cortex contralateral to the stimulated cortex increased the threshold for @entity910 and medullary pyramidal lesions ipsilateral to the stimulated cortex both reduced the number of responses and increased the threshold current intensities needed to evoke them. These data indicate that hemicerebellectomy within 3 weeks of age can induce electrophysiological alterations in the responses mediated by the corticospinal tract. These results support previous suggestions of the cerebral cortical involvement in compensation for @entity76 .
