A new study has suggested that rats can recall how much time has passed since they discovered a piece of cheese, but they simply cannot recall when they found it.
William Roberts, a researcher in the Department of Psychology at The University of Western Ontario, says that this finding indicates that rats cannot place memories in time.
A Science magazine report, which describes the study, reveals that rats visited the 'arms' of a maze at different times of day. Some arms contained moderately desirable food pellets, and one arm contained a highly desirable piece of cheese.
The animals were later returned to the maze with the cheese removed on certain trials, and with the cheese replaced with a pellet on others.
Robert's team used three varying cues as to when, how long ago, and when and how long ago three groups of rats, respectively, encountered the food.
The only cue that rats used successfully was of how long ago they encountered food.
The researchers say that the observations made during the study suggest that episodic-like memory in rats is qualitatively different from human episodic memory, which involves retention of the point in past time when an event occurred.
"The rats remember whether they did something, such as hoarded food a few hours or five days ago," says Roberts.
"The more time that has passed, the weaker the memory may be. 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," he adds.
While previous studies had suggested that rats and scrub jays-a relative of the crow and the blue jay-appeared to remember storing or discovering various foods, it has been unclear whether they could remember exactly when such events happened or how much time had elapsed.
"This research, supports the theory I introduced that animals are stuck in time, with no sense of time extending into the past or future," said Roberts.