"Four groups of rats, two experimental and two control, were trained to jump at the onset of a light. On the next day, experimental rats were subjected to extensive unilateral posterior cortical ablations. One experimental and one control group spent the next 12 days in the home cages; the other two were transferred to a lightproof chamber for the same period of time. Afterward, all experimental rats were operated for removal of the remaining contralateral posterior region of the brain, and then all groups were transferred to home cages for a 6-day period prior to being tested for retention through retraining in the habit. Sparing was noted in all groups except the one composed of operated animals that spent the interoperative interval in darkness. Thus, extrinsic factors have been shown to be of critical importance for retention, and the process of reorganization is not aptly call "spontaneous." From Psyc Abstracts 36:01:1EH46M. (PsycINFO Database Record (c) 2006 APA, all rights reserved)