Since the time of the ancient Greeks, we have known that two tones whose frequencies were related by a simple ratio like 2:1 (an octave) or 3:2 (a perfect fifth) produce the most pleasing, or consonant, musical intervals. This effect doesn't depend on musical training – <a href="http://jn.physiology.org/content/86/6/2761.short" target="_blank" class="news_link">infants and even monkeys</a> can hear the difference. But it was unclear whether consonant chords are easier on the ears because of the way <a href="http://www.newscientist.com/article/mg20627591.300-harmonious-minds-the-hunt-for-universal-music.html" target="_blank" class="news_link">the sound waves combine in the air, or the way our brains convert them to electrical impulses</a>. A new mathematical model presents a strong case for the brain.


"We have found that the reason for this difference is somewhere at the level of neurons," says Yuriy Ushakov at the N. I. Lobachevsky State University of Nizhniy Novgorod in Russia.


Ushakov and colleagues considered a simple mathematical model of the way sound travels from the ear to the brain. In their model, two sensory neurons react to different tones. Each sends an electrical signal to a third neuron, called an interneuron, which sends a final signal to the brain. The model's interneuron fires when it receives input from either or both sensory neurons



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Why harmony pleases the brain