Long-term impact of early olfactory experience on later olfactory conditioning

This study examined the duration of the effect of early olfactory experience in rats by determining the ease of conditioning and then reconditioning to an early-experienced odor. Rat pups (experimental group) were exposed to aniseed odor sprayed on the mother's belly from day 1 to 20 after birth. A control group was exposed only to water. At the ages of 21 and 40 days all the rats (experimental and control) were tested for preference for the odor of aniseed. Starting from day 41 after birth they were conditioned in a Y-maze to approach the odor of aniseed for a reward. We then divided both groups into five subgroups each. Each subgroup was retrained to approach aniseed after 5, 6, 7, 8 or 9 months, and their speeds of reconditioning to the odor were compared. The results showed that all rats in the early exposed group had remembered the odor and did not require reconditioning, unlike those in the group that had not had the early olfactory conditioning. The effect of the early experience was still detectable at least 5 months after last exposure to the odor.