The first experiments with neural transplantation into the brain (for a review, see Bjorklund and Stenevi 1985) were reported at the end of the last century by Thompson (1890), who took cortical tissue from adult cats and implanted the tissue pieces into the neocortex of adult dogs. The neurons did not survive, but the transplanted mass did not disintegrate entirely. Successful graft ing into the brain was reported later by Ranson (1909), who implanted spinal ganglia into the cerebral cort...