By Tuan C. Nguyen, LiveScience Staff Writer
posted: 30 September 2007 10:14 am ET
Cockroaches learn new tricks well in the evening, but they're lousy students in the morning.
A new study, published in the Proceedings of the National Academy of Sciences, showed that while cockroaches were able to pick up and remember lessons taught in the evenings, they might as well have stayed in bed during the morning hours.
Similar research performed on rodents suggested that the ability to learn and retain lessons is regulated by "biological clocks," which adjust the body's alertness and hormone levels over a 24-hour cycle. One study even revealed that mice subjected to jet lag—a sudden disruption to the biological clock—were more likely to die.
"This is the first example of an insect whose ability to learn is controlled by its biological clock," said researcher Terry L. Page of Vanderbilt University.
To figure out how a cockroach's biological clock impacted its learning ability, the scientists at Vanderbilt University trained cockroaches—at different times of the day—to associate the normally disliked scent of peppermint with tasty sugar water, so that they would favor it over vanilla smells, which they typically preferred.
"With the cockroaches trained in the morning, we were quite surprised at the profound learning deficit the next day," Page said. "They forgot everything and behaved as if they had no training at all."
Page noted that although they have no idea why cockroaches don't learn at that particular time of day, these kinds of studies can give insight into the interaction between learning, memory and biological clocks, as well as what can influence these processes in other creatures.
Humans also are affected by a circadian rhythm. Most previous studies of the mechanism have focused on the visual system.
"The advantage of eyes becoming more sensitive at night is so obvious that people haven’t looked much at other sensory systems," says Page. "The fact that our study involves the olfactory system suggests that the circadian cycle could be influencing a number of senses beyond vision."
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