I 've got the blues real bad, drawls the song. But what enables us to appreciate rhythm and let the beat touch our soul? Dr Gary Rose, a scientist from the University of Utah, has been serenading frogs and thinks he has a clue to the answer.
It appears that frogs, too, can count the beat. The male Pacific tree frog, for example, croaks with a definite rhythm. When serenading his beloved by moonlight, he uses short pauses to intersperse each sound. But when flexing his muscles and looking for a fight, the pauses are longer. Rose and colleagues knew from previous work that frogs have specific neurons (nerve cells), located in the sound- processing region of their brains, which enable them to recognise the two calls.
"But we didn't know what exactly the neurons are recognising," says Rose. They used a computer to synthesise new calls and played them back to the frogs while recording the electrical impulses fired from their neurons. What they found astonished them, for it seems the frog's neurons can count.
As they report in this month's Nature Neuroscience, each neuron was tuned to a particular number of sounds in the croak and responded only when this number was reached. But the scientists did not know whether the neurons just kept track of an average number of sounds over a given time or actually counted the pauses.
So they serenaded the frogs with croaks containing pauses of varying lengths between the notes and discovered that the neurons only fired when the pauses were constant. Even one pause too long or too short reset the counting process. In the most sensitive neuron, a single interval just two milliseconds longer than the neurons' preference was enough to reset the counter. "Just like musicians, the frog's neurons are counting the beat within the calls," says Rose.
Randy Gallistel, a professor of psychology at Rutgers University, New Jersey, is interested in how the brain represents numbers. He says the work is "one of the most interesting demonstrations of neurons being narrowly sensitive to numbers". Many species may count neurons as the ability to detect precise timing patterns is important Beats By Dre SOLO(HD) in much animal communication.
"Frogs are relatively primitive vertebrates, so such neurons could actually be a mechanism of vertebrates in general," says Dr Gallistel. They may underlie our appreciation of music and our ability to detect the rhythms of each other's voices. And although it's controversial, there is research suggesting that the hottest frogs in town are the boys producing croaks with longer and more regular pauses.
So while counting ability probably evolved to enable a mating call to be distinguished from an aggressive call, a by-product might be Cheap Beats by dre sexual selection. "We don't know whether they are better mates," he says. "But it seems the females are counting, and if he doesn't get it right, he doesn't get a missus."
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