1. A method of treating a mammal afflicted with a seizure disorder, the method comprising: transplanting medial ganglionic eminence (MGE) cells into the central nervous system of a mammal afflicted with a seizure disorder; and allowing the transplanted cells to migrate and integrate in the central nervous system of said mammal to form functional inhibitory interneurons that are associated with a reduction in seizure activity in said mammal, thereby treating the seizure disorder in said mammal.