Rats take fast route to remembering

People call on a rich background of relevant experiences to organize and remember new material. Rats do the same, and with surprising speed, say Dorothy Tse of the University of Edinburgh and her coworkers.

Prior studies, which have focused on task learning unrelated to preexisting knowledge, indicate that a brain region called the hippocampus incorporates new facts and events into memory. The hippocampus gradually yields to another structure, the neocortex, as new memories become stronger. This process typically takes at least 1 month in rodents and a few years in people.

Tse’s team trained groups of rats to associate six flavors, including banana and bacon, with six designated spots within a laboratory-test area. Rats received food with a particular flavor in one of four entries to the area and then could obtain more of it by going to the correct location. The animals learned all six flavor-place associations in 1 month.

Further experiments indicated that the animals had also developed a framework of knowledge about relations between places and flavors that enabled them to learn new pairings remarkably quickly. The rats remembered novel flavor-place associations after just one trial and retained this information for at least 2 weeks, the scientists report in the April 6 Science.

The rats’ formation of a knowledge framework spurred the neocortex to integrate new information into memory in record time, the scientists propose. Surgical removal of the hippocampus 48 hours after the rats had rapidly learned new flavor-place associations left those memories intact, a sign that the neocortex had already taken charge of the material.