The time machine

It all comes down to cheese. Can rats remember when they ate it? Can rats put their memories of cheese-eating in a chronology? Researchers at The University of Western Ontario say their rats couldn't.

In research presented in the latest issue of Science, William Roberts and his colleagues in the psychology department found that rats had memories but couldn't place the memories in a continuum with an appreciation of past, present, and future. The rats could track how much time had passed since they nabbed a piece of comestible dairy, but according to tests formulated by the researchers, they couldn't form a memory of the event and place it in time among other events.

In the study, rats were sent to different areas of a maze. Food pellets sat in some areas, and a piece of delicious cheese was in one arm of the maze. Later, the rats were returned to the maze with the cheese removed or replaced by pellets. The rats seemed to know how long ago they saw the cheese, but they couldn't put two and two together and figure out when that cheese might show up again.

"The rats remember whether they did something, such as hoarded food a few hours or five days ago," Roberts says. "Rats may learn to follow different courses of action using weak and strong memory traces as cues, thus responding differently depending on how long ago an event occurred. However, they do not remember that the event occurred at a specific point in past time."

Roberts says the research shows animals are "stuck in time." They form memories about events, but can't place them in definite points in the past or anticipate exactly when they'll happen again in the future.