Cockroaches: stupid in the morning, geniuses in the evening

Learning ability is dependent on the internal clock

American Cockroach © Creative Commons 2.0
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For most, cockroaches are annoying pests, but they have now given American biologists an amazing insight into the influence of the Inner Clock on learning behavior. Because this fluctuated dramatically in the insects depending on the time of day, the researchers reported in the journal "Proceedings of the National Academy of Sciences".

Earlier, scientists discovered in learning experiments with mammals that their learning ability fluctuated with the time of day. Even in humans, such variations occur. It showed a recent attempt that the learning ability is particularly bad when the internal clock is disturbed, for example by a jet lag, but also at certain times of the day. An experiment on rats also confirmed a connection between jet lag and forgetfulness.

Learning effect in the morning at zero

In the current study, scientists from Vanderbilt University helped individual cockroaches of the species Leucophaea maderae associate peppermint scent with sugar water. Usually a hateful smell, the animals even learned to prefer this to the very popular vanilla fragrance. To find out if the learning ability changes during the day, the researchers trained the cockroaches at different times and observed how long they retained the memory of what they had learned.

It turned out that the cockroaches trained in the evening remembered the connection between peppermint and sugar water for several days. Similar to those who received their lessons at night. Quite different, however, the morning learners: they were completely unable to memorize new things, but at least they could retrieve the learned at other times.

Mechanism still unclear

"This is the first example of an insect whose learning ability is controlled by the internal clock, " explains Terry L. Page, Professor of Life Sciences at Vanderbilt University. "It's very surprising that the deficit in the morning is so fundamental. An interesting question is why the animal can not learn at this time of day. So far we have no idea why. "Ad

Inner clock controls cockroaches learning behavior. SXC

The discovery that the cockroaches' memory is so strongly influenced by the inner clock opens up new possibilities to find out more about the molecular basis of the interplay between learning and the inner clock. Because a large part of the previous findings comes from experiments with insects and other invertebrates. "Studies like this indicate that the time of day can have a strong impact, at least in certain situations, " he says. "By studying how the Inner Clock modulates learning and memory, we also learn more about how these processes work and how we can influence them."

(Vanderbilt University, 28.09.2007 - NPO)