A study by biologists at Vanderbilt University in Nashville, Tennessee, found dramatic variations in a cockroach’s learning ability throughout the day. In the morning, the insects couldn’t learn a new task, but in the evening, something kicked in.
"This is the first example of an insect whose ability to learn is controlled by its biological clock," Terry L. Page, professor of biological sciences, said on Friday.
"This study was a surprise from the beginning to the end –the fact that cockroaches could be trained, even though you would not generally say they are a high IQ creature, and the impact that their body clocks had on their ability to learn."
During the two-year study, published in the Proceedings of the National Academy of Sciences, researchers taught cockroaches to associate peppermint — a scent that the critters normally dislike — with sugar water so that they favored it over one of their favorite smells, vanilla.
The researchers trained several hundred cockroaches at different times throughout a day and tested them to see how long they remembered the association.
The cockroaches trained during the evening and at night, when they tend to be more active, remembered what they had learned for several days. But the bugs trained in the morning were incapable of learning something new and remembering it.
"It is very surprising that the deficit in the morning is so profound," said Page, who lead the study. "An interesting question is why the animal would not want to learn at that particular time of day. We have no idea."
He said the study could provide insight into links between biological clocks, memory and learning for other animals and humans.