Ontogenetic differences in the expression of odor-aversion learning in 4- 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.