Mapping of the rat's motor area after hemispherectomy: The hemispheres as potentially independent motor brains

Purpose: The remarkable motor recovery observed after hemispherectomy in patients and experimental animals has puzzled investigators, as it defies classic jacksonian neurology. Several mechanisms for this phenomenon have been considered, such as neuronal sprouting to subcortical structures, neurochemical changes, and cerebellar diaschisis. The spared hemisphere may, however, play a crucial part in this functional recovery. Methods: In this study, seven Wistar rats were submitted to right hemisphere motor area mapping. In the same anesthetic time, a left microsurgical hemispherectomy was performed, and the animal allowed to recover for 2 weeks. After then, the right hemisphere was again stimulated for its motor area. Results: Four rats had, after 2 weeks of observation, bilateral body movements with stimulation of only the right hemisphere. The same segments on both sides had symmetric and simultaneous movements. Conclusions: The results suggest that each motor area has the latent capacity to control motricity bilaterally, and that such capacity is brought into function after removal of the opposite hemisphere. The same neuronal population that gives afference to one segment contralaterally seems to give afference to the same segment ipsilaterally.