Odor-aversion learning in neonatal rats.

Two-day-old rats were exposed to a novel odor and injected with an illness-inducing drug, lithium chloride. When tested at 8 days of age, these pups avoided pine shavings scented with the odor, whereas control pups did not. These results imply that rat pups are capable of associative learning at a much earlier age than was thought possible.