Ontogenetic adaptation and learning: a developmental constraint in learning for a thermal reinforcer.

Hoffman, Flory, and Alberts (1999) demonstrated that 1-, 5-, and 11-day-old rats in a cool environment (25 degrees C) acquired an operant head-turning response when rewarded with a 20-s warming of the platform on which they lay. In the current experiment 5- and 11-day-old rats in a hot environment (40 degrees C) acquired the head-turning response when rewarded with a 20-s cooling of the platform on which they lay, but 1-day-olds did not. The concept of ontogenetic adaptation helps us interpret these results: Neonatal thermotaxis constrains the 1-day-olds from learning a novel operant response for a cool reinforcer in a hot environment. Because the thermotaxis wanes from birth, it is not as strong in 5- and 11-day-old pups that are thus able to learn the operant for a cool reinforcer.