The role of the dorsal CA1 and ventral CA1 in memory for the temporal order of a sequence of odors

Memory for the temporal order of a sequence of odors was assessed in male rats. A sequence of five odors mixed in sand was presented in digging cups one at a time to each rat in a sequence that varied on each trial. A reward was buried in each cup. Following the fifth odor, two of the previous five odors were presented simultaneously and the rat needed to choose the odor that occurred earliest in the sequence to receive a reward. Temporal separations of 1, 2, or 3 were used which represented the number of odors that occurred between the two odors in the sequence. Once pre-operative criterion was reached, rats received a control, dorsal CA1 (dCA1), or ventral CA1 (vCA1) lesion and were retested on the task. On post-operative trials, only the vCA1 group was impaired relative to both control and dCA1 groups. All groups of rats could discriminate between the odors. The data suggest that the vCA1, but not dorsal CA1, is involved in separating sensory events (odors) in time so that one odor can be remembered separate from another odor.