Conditioned aversion is promoted by memory of CS-

Abstract

Five experiments tested the effects of experience with a white compartment not paired with footshock (CS-) on conditioning of an aversion to a black compartment paired with footshock. As previously found with odors as CSs, a single pairing of the CS+ with footshock yielded significant conditioning only if the animal was also exposed to CS-, with greater conditioning when the CS- exposure preceded the CS+ than when the CS+ preceded the CS-. If, however, the CS- preceded CS+ by a 24-h interval, it was ineffective and no CS+ conditioning occurred. For adult rats, the effectiveness of the CS-/CS+ "integration" progressively decreased with increasing length of the interval separating their occurrence, although it was still significant (i.e., some CS+ conditioning occurred) with a 12-h CS- to CS+ delay. For preweanlings (16 days postnatal), no conditioning to CS+ occurred if the interval between CS- and CS+ was 1 h or longer, although significant conditioning to CS+ did occur with a CS- to CS+ interval as long as 40 min. It was as if active memory for the CS- at the time of CS+ exposure was necessary for CS+ conditioning, and forgetting of the CS- memory proceeded more rapidly for preweanling than for adult rats. Collectively, these experiments extend results previously indicating that (1) the CS+ contiguous to the US may or may not be "selected" for conditioning, depending on the rat's exposure to, or memory for, a CS-, and (2) this stimulus selection might differ for immature and mature rats. © 1985 Psychonomic Society, Inc.