Cockroaches have a memory and can be taught to salivate in response to neutral stimuli in the way that Pavlov's dogs would do when the famed Russian doctor rang his bell, Japanese researchers found.
Such "conditioning" can only take place when there is memory and learning, and this salivating response had only previously been proven in humans and dogs.
Now, cockroaches appear to have that aptitude too.
Writing in the latest edition of the online journal Public Library of Science, the researchers said they hoped to learn more about the human brain by exploring what goes on in the simpler brain of the cockroach. (Article is freely available on http://www.plosone.org/doi/pone.0000529)
"Understanding the brain mechanism of learning in insects can help us to understand the functionings in the human brain. There are many, many common characteristics," said Makoto Mizunami, of Tohoku University's Graduate School of Life Sciences, in a telephone interview.
In the experiment, the scientists exposed a group of cockroaches to an odour whenever they fed them a sugar solution. They found that when they later exposed the cockroaches to the odour alone, they still drooled.
Another group of cockroaches was fed the sugar solution without the odour, and exposure to the smell afterwards caused no change in the amount of saliva produced.
"Sure, cockroaches can remember and learn," Mizunami said.
In the 1890s and 1890s, Russian doctor Ivan Petrovich Pavlov conducted research into what is now known as "classical conditioning" with dogs.
He used bells to call dogs to their food and, after a few repetitions, the dogs began to salivate in response to the bell.
But until today, and despite the advances of science, little is known about the mammalian brain and its neural mechanisms because they are so complex.
Mizunami said his team would find out what takes place in the cockroach's brain next.
"In the cockroach's brain, there are many, many neurons and we have to find which neuron is actually responsible for this learning," he said.
"We believe that it is very important to study a simple system to very precisely determine what is happening during learning. We hope it is at least in part applicable to humans."