Ontogenetic differences in the expression of conditioned visual aversions.

We examined ontogenetic differences in the expression of conditioned visual aversions. Sprague-Dawley-derived rats, 16 or 21 days of age, were conditioned with either an element (brightness) or compound (brightness/odor) CS+ and tested for their aversion to the common element (brightness). Aversions to the brightness cue were assessed by either a traditional test of preference between the CS+ brightness and a contrasting brightness or by assessment of freezing in the presence of either brightness cue.