Heading out of the hippocampus.

Despite the hippocampus' powerful influence on episodic memory, other brain areas may independently gather and retrieve information that animals use to orient themselves in a new setting, according to a report in the July 8 Proceedings of the National Academy of Sciences.

This surprising finding is compatible with the notion that parts of the cortex can facilitate some facets of spatial memory, even without an intact hippocampus, hold Edward J. Golob and Jeffrey S. Taube, both psychologists at Dartmouth College in Hanover, N.H.

Golob and Taube trained seven rats to search for food pellets placed at random in variously shaped enclosures by first orienting themselves with respect to a colored cue card taped to the wall; the card served as a constant reference point. Most or all of each rat's hippocampus was then removed.

Afterwards, when the rats searched for food in unfamiliar enclosures, brain cells at sites outside the hippocampus emitted electrical discharges keyed to the animals' head directions, just as they did before the hippocampal damage. Over several days of testing, a particular test space evoked the same neural response pattern at those brain sites.

Cortical structures related to vision may absorb information about the spatial features of new surroundings, the researchers suggest. Animals may then retrieve that information on return trips and use it to gauge the direction in which they're facing.