ABSTRACT
Until recently, the general opinion was common that the mature brain is rather stable or fixed in functional organization. This general opinion seemed to be based on two major lines of evidence. As an example of one type of evidence, Sperry (1943) showed that altering inputs into the mature brain of mature rats failed to produce adaptive adjustments in behavior. Specifically, Sperry crossed sensory nerves from one hindlimb to the other and allowed regeneration of the cut nerve into the skin of the wrong limb. When the newly innervated skin was pinched, the rats retracted the original limb rather than the newly innervated limb, and this behavior persisted. We repeated these experiments with exactly the same behavioral results (Wunderlick, Wall, & Kaas, 1981). Rats consistently retracted the original rather than the pinched leg. Recordings in the somatosensory cortex showed no adaptive reorganization that would alter this behavior. In regard to this manipulation, no adaptive change in behavior occurred, and no relevant reorganization of the somatosensory system was observed. Sperry, on the basis of the behavioral observations alone, concluded that the mature nervous system was not very plastic.
