Figure 1. Incidental order and item memory task.

A, Odors (household spices) were presented one at a time on wooden beads in front of the cage and centered. The time spent exploring the first odor (during a 30 s exposure) set the criterion exploration time for the remaining odors in the sequence. After a 60 min retention interval, subjects were given an order probe in which two odors from the sequence were presented (B vs. D) separated by ~6 cm. Preferential exploration on the odor that came earlier (B) indicated memory for order. Twenty minutes later, an item probe was presented in the same way except that it involved a comparison between another odor from the sequence and a novel odor (C vs. X). Preferential exploration toward the novel odor (X) indicated memory for the items presented in the sequence. B, All behavior was performed within each individual rat’s home cage, and active investigation time (sniffing and whisking within 1 cm of bead) was scored for each odor. Each bead was only used once to eliminate the possibility of contamination and/or change in odor strength. Therefore, when a sample odor was presented in the order or item probe, it was on a different bead (which was incubated in the same container for the same period of time).