The development of intersession habituation and emergence in socially reared and isolated rats.

Male and female hooded rats were weaned at 17 days and then reared in isolation or in social groups. Intersession habituation of locomotor activity in the open field was tested at 15, 25, and 45 days. Contrary to some previous reports, the 15-day-old animals showed significant habituation. At 45 days, however, the isolates showed very little habituation compared to the social animals. The isolates showed a similar pattern of development in their emergence into the open field. Apparently, isolation does not result in an arresting of development, but rather in the formation of behavior patterns otherwise absent in normally reared rats.