The Hippocampus and Memory for What, Where, and When

Previous Studies have indicated that nonhuman animals might have a capacity for episodic-like recall reflected in memory for what events that happened where and when. These studies did not identify the brain structures that are critical to this capacity. Here we trained rats to remember single training episodes, each composed of a series of odors presented in different places on an open field. Additional assessments examined the individual contributions of odor and spatial cues to judgments about the order of events. The results indicated that normal rats used a combination of spatial (where) and olfactory (what) cues to distinguish when events Occurred. Rats with lesions of the hippocampus failed ill using combinations of spatial and olfactory cues, even as evidence from probe tests and initial sampling behavior indicated spared capacities for perception of spatial and odor cues, as well as some form of memory for those individual cues. These findings indicate that rats integrate what, where, and when information in memory for single experiences, and that the hippocampus is critical to this capacity.