Environmental stimulation reduces learning deficits in experimental cretinism.

Behavioral deficits in adult rats exposed perinatally to thiouracil were substantially reduced or elimated by a 5-week period of "superenriched" postweaning rearing conditions before testing. This treatment resulted in remediation of hypothyroid rats' deficits in maze learning, maze retention, and resistance to extinction of bar-pressing; the facilitative effect persisted for more than 4 months. These behavioral results were consistent with neurohistological findings from studies of early thyroid deficiency and postweaning environmental stimulation in rats.