April 3, 2008
Can Animals Tell Time?
William Roberts and his colleagues at the University of
Western Ontario found that rats are able to keep track of how much time has
passed since they discovered a piece of cheese, be it a little or a lot, but
they don't actually form memories of when the discovery occurred.
The rats can't place the memories in time, Roberts and
colleagues report this week in the journal Science.
The researchers designed an experiment in which 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. Rats were later returned to the maze with the cheese removed on certain
trials and with the cheese replaced with a pellet on others.
Three groups were tested using three varying cues: when,
how long ago or when plus how long ago.
Only the cue of how long ago food was encountered was
used successfully by the rats.
"The rats remember whether they did something, such
as hoarded food a few hours or five days ago," Roberts said. "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
Previous studies have suggested that rats and scrub jays
(a relative of the crow and the blue jay) appear to remember storing or
discovering various foods, but it hasn't been clear whether the animals were
remembering exactly when these events happened or how much time had elapsed.
"This research," said Roberts, "supports
the theory I introduced that animals are stuck in time, with no sense of time
extending into the past or future."