ONTOGENIC DIFFERENCES IN THE EXPRESSION OF ODOR-AVERSION LEARNING IN 4-DAY-OLD AND 8-DAY-OLD RATS

Two experiments investigated the ability of preweanling rats, 4 or 8 days of age, to form an odor‐LiCl association across various CS‐US delays. The results of the odor preference test indicated that 8‐day‐old subjects acquired an aversion to the CS+ odor when trained with either a 0 or 15 min CS‐US delay, while 4‐day‐old subjects did not exhibit a reduction in preference for the CS+ at any of the CS‐US delays tested. The absence of a reduction in preference for the CS+ by 4‐day‐old rats could not be attributed to their failure to acquire the odor aversion, however; they avoided a texture with which the CS+ odor was paired in a second order conditioning paradigm. The results suggest that outcomes appearing to represent age‐related differences in associative learning may in some instances be more appropriately viewed as representing ontogenetic differences in the way in which acquired associations are manifested in behavior. Copyright © 1990 John Wiley & Sons, Inc.