After 5 minutes, the hamster is removed from the box, and one of the objects is replaced with a new, different object. After a span of time-in Ruby's study, the time was varied between 20 minutes and an hour-the hamster is put back in the box.
"A normal animal will spend time with both objects, but it will spend easily twice as much time with the new one," Ruby said. "It understands that it has seen the other one before."
But when a hamster that lacks circadian rhythms is put back in the box, it's as if it is a whole new world for the hamster. Whether the hamster is out of the box for an hour or as short a time as 20 minutes, it spends the same amount of time with each object, Ruby said.
"What that means is they don't remember the object that was in there before," he said.
The finding is even more striking when you consider that when a hamster loses its circadian system, it gets even more sleep than usual.
"What our data are showing is that these animals still performed terribly on a simple learning task, even though they're getting loads of sleep," Ruby said. "What this says is that the circadian system really is necessary for something that is deeply important: learning."
|Contact: Louis Bergeron|