ONTOGENY OF 2ND-ORDER ODOR-AVERSION CONDITIONING IN NEONATAL RATS

In Exp I, 102 Sprague-Dawley rat pups 1, 3, 5, or 7 days old received a Phase 1 Stimulus 1 (S1)-UCS pairing calculated to establish a 1st-order conditioned aversion to S1 (lemon scent). On the next day each pup received a Phase 2 S2-S1 pairing designed to establish a 2nd-order aversion to S2 (orange scent). Ss at all ages displayed a 1st-order aversion to S1, but only Ss given Phase 2 training when 6 or 8 days old displayed a 2nd-order aversion to S2. Exp II revealed that 52 Ss that received the S1-UCS pairing when 3 days old acquired an aversion to S2 if they were 6 days old when they received the S2-S1 pairing but not if they received the pairing when 4 days old. In Exp III, 2 Phase 2 treatments were compared. One was identical to that employed in Exps I and II: 15 4-day-old Ss received a sequential exposure to S2 and S1. Seven Ss were exposed first to S2 and then jointly to both S2 and S1. Only Ss in the latter set displayed an aversion of S2. These results reflect developmental differences in the memory processes mediating the rat's experience with olfactory stimulation. (16 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.