"This is also important because it is one of the first lines of evidence that shows losing your circadian timing actually does cost you something," Ruby said. "It makes it hard to learn things. And the underlying mechanism is that you have too much GABA."
Ruby said researchers have known since the early '70s that the circadian system modulates learning in humans and other animals, but no one knew what the effect would be on learning if the system was completely wiped out. Laboratory animals-rats, mice and hamsters-whose circadian systems have been disabled as part of a study typically live long and healthy lives.
"We thought it might be possible to wipe out circadian rhythms and eliminate the rhythm in learning, but that the animals could still learn something," Ruby said. "But they don't. That is what was so surprising. They actually can't remember anything. Losing their rhythms costs them a lot."
The researchers knocked the hamsters' circadian systems out of commission using a new noninvasive technique they developed involving manipulating the hamsters' exposure to light. The hamsters were first exposed to two hours of bright light late at night. Then the next day the researchers delayed the usual light/dark cycle by three hours. "It is like sending them west three time zones," Ruby said.
After the treatment, the normal light/dark cycle is resumed, but that one-time treatment is enough to wipe out their circadian system.
To assess the effect of the treatment, Ruby's team conducted a standard test called a novel object recognition task that takes advantage of animals' innate tendency to explore their environment. Using a box roughly 2 feet square, the researchers put two identical
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