Learning during the newborn's first meal: special resistance to retroactive interference.

At their first postnatal meal, 3-hour-old rats learned an association between an odor and a sweet or bitter taste. Retention after a long interval or after associative interference was compared to that of 1-day-old rats. Despite equivalent and negligible effect of the long retention interval, contrary to infantile amnesia, newborns differed strikingly from 1-day-olds in susceptibility to associative interference. When lemon odor predicted saccharin in the first episode but quinine in the second, 1-day-olds had strong retroactive interference, but the newborn's first memory was unaffected by the second. The results were identical when the first memory was a lemon-quinine association and the second a lemon-saccharin association. It is uncertain whether this special robustness of memories associated with the first postnatal meal is best understood in terms of cognitive primacy or neurochemical and physiological consequences of the birth process.