The key to pleasant music may be that it pleases our neurons. A new model suggests that【C1】______musical intervals trigger a rhythmically【C2】______ firing pattern in certain auditory neurons, and that sweet sounds carry more information than【C3】______ones. 【C4】______ the time of the ancient Greeks, we have known that two tones whose【C5】______ were related by a simple ratio like 2:1 or 3: 2 produce the most pleasing, or consonant, musical intervals. This effect doesnt depend on musical【C6】______—infants and even monkeys can hear the difference. But it was unclear whether consonant chords are easier on the ears【C7】______the way the sound waves combine in the air, or the way our brains【C8】______ them to electrical impulses. A new mathematical model presents a strong【C9】______for the brain. 'We have found that the reason for this difference is【C10】______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 【C11】______from the ear to the brain. In their model, two sensory neurons 【C12】______ to different tones. Each sends an electrical signal to a third neuron, called an interneuron, which sends a final signal to the brain. The models interneuron fires【C13】______ it receives input from【C14】______ or both sensory neurons.【C15】______, the signals from the sensory neurons arrive at the same time if the tone is consonant, and so the interneuron still fires just once, then waits until it '【C16】______' before it fires again. The result is a(n) 【C17】______train of pulses. 【C18】______, the signals from harsh tones arrive at【C19】______times and so generate an【C20】______ spaced train of pulses in the interneuron. 【C1】