Cockroaches are morons in the morning, geniuses in the evening

September 27, 2007

In its ability to learn, the cockroach is a moron in the morning and a genius in the evening. Dramatic daily variations in the cockroach’s learning ability were discovered by a new study performed by Vanderbilt University biologists and published online this week in the Proceedings of the National Academy of Sciences.

“This is the first example of an insect whose ability to learn is controlled by its biological clock,” says Terry L. Page, the professor of biological sciences who directed the project. Undergraduate students Susan Decker and Shannon McConnaughey also participated in the study.

The few studies that have been done with mammals suggest their ability to learn also varies with the time of day. For example, a recent experiment with humans found that people’s ability to acquire new information is reduced when their biological clocks are disrupted, particularly at certain times of day. Similarly, several learning and memory studies with rodents have found that these processes are modulated by their circadian clocks. One study in rats associated jet lag with retrograde amnesia.

In the current study, the researchers taught individual cockroaches to associate peppermint – a scent that they normally find slightly distasteful – with sugar water, causing them to favor it over vanilla, a scent they find universally appealing.

The researchers trained individual cockroaches at different times in the 24-hour day/night cycle and then tested them to see how long they remembered the association. They found that the individuals trained during the evening retained the memory for several days. Those trained at night also had good retention. During the morning, however, when the cockroaches are least active, they were totally incapable of forming a new memory, although they could recall memories learned at other times.

“It is very surprising that the deficit in the morning is so profound,” says Page. “An interesting question is why the animal would not want to learn at that particular time of day. We have no idea.”

Most previous studies of circadian rhythm 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.”

In the study, the researchers used cockroaches of the species Leucophaea maderae. It doesn’t have a common name but it is commonly used in scientific experiments because it was used extensively in early physiological and endocrinological studies.

The discovery that the cockroach’s memory is so strongly modulated by its circadian clock opens up new opportunities to learn more about the molecular basis of the interaction between biological clocks and memory and learning in general.

Much of the new information about the molecular basis of memory and learning has come from the study of other invertebrates (animals without backbones) such as the sea slug (Apylsia) and the fruit fly (Drosophila).

“Studies like this suggest that time of day can have a profound impact, at least in certain situations. By studying the way the biological clock modulates learning and memory we may learn more about how these processes take place and what can influence them,” Page says.

Source: Vanderbilt University

Explore further: Changing clocks and changing seasons: Scientists find role for neuronal plasticity

Related Stories

Eris' moon Dysnomia

July 29, 2015

Ask a person what Dysnomia refers to, and they might venture that it's a medical condition. In truth, they would be correct. But in addition to being a condition that affects the memory (where people have a hard time remembering ...

Recommended for you

Magnetism at nanoscale

August 3, 2015

As the demand grows for ever smaller, smarter electronics, so does the demand for understanding materials' behavior at ever smaller scales. Physicists at the U.S. Department of Energy's Ames Laboratory are building a unique ...

How the finch changes its tune

August 3, 2015

Like top musicians, songbirds train from a young age to weed out errors and trim variability from their songs, ultimately becoming consistent and reliable performers. But as with human musicians, even the best are not machines. ...

Study calculates the speed of ice formation

August 3, 2015

Researchers at Princeton University have for the first time directly calculated the rate at which water crystallizes into ice in a realistic computer model of water molecules. The simulations, which were carried out on supercomputers, ...

Small tilt in magnets makes them viable memory chips

August 3, 2015

University of California, Berkeley, researchers have discovered a new way to switch the polarization of nanomagnets, paving the way for high-density storage to move from hard disks onto integrated circuits.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.