Reorganization of cerebral control of tactile placing after interrupting a spinal ascending system in cats with pyramid section.

Interruption of a spinal ascending system by hemisection of the spinal cord at mid-thoracic level restores the tactile placing (TP) which is lost after bulbar pyramid section in cats. To determine the location of the ascending system in the spinal cord, partial lesions involving various dorsal, lateral, or ventral tracts were made at mid-thoracic level in cats with pyramid section. To determine the supraspinal control of the recovered TP after pyramid section and spinal cord hemisection, lesions were made in other cortical and subcortical structures essential to TP and also in cortical areas which are not normally involved in TP in cats with recovered TP. The findings demonstrate that the spinal ascending system is located in the ventral part of the lateral funiculus and that the cerebral association cortex takes over the function of motor cortex in the reorganized control of TP. A slow course of TP recovery along with no recovery of impaired distal forelimb movements resulting from pyramidotomy were also observed.