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Why do people always want to get up and dance when they hear music? The usual explanation is that there is something embedded in every culture—that dancing is a 'cultural universal'. A researcher in Manchester thinks the impulse may be even more deeply rooted than that. He says it may be a reflex reaction. Neil Todd, a psychologist at the University of Manchester, told that he first got an inkling that biology was the key after watching people dance to deafeningly loud music. 'There is a compulsion about it,' he says. He reckoned there might be a more direct, biological, explanation for the desire to dance, so he started to look at the inner ear. The human ear has two main functions: hearing and maintaining balance. The standard view is that these tasks are segregated so that organs for balance, for instance, do not have an acoustic function. But Todd says animal studies have shown that the sacculus, which is part of the balance-regulating vestibular system, has retained some sensitivity to sound. The sacculus is especially sensitive to extremely loud noise, above 70 decibels. 'There's no question that in a contemporary dance environment, the sacculus will be stimulated,' says Todd. The average rave, he says, blares music at a painful 110 to 140 decibels. But no one really knows what an acoustically stimulated sacculus does. Todd speculates that listening to extremely loud music is a form of 'vestibular self-stimulation': it gives a heightened sensation of motion. 'We don't know exactly why it causes pleasure,' he says. 'But we know that people go to extraordinary lengths to get it.' He lists bungee jumping, playing on swings or even rocking to and fro in a rocking chair as other examples of pursuits designed to stimulate the sacculus. The same pulsing that makes us feel as though we are moving may make us get up and dance as well, says Todd. Loud music sends signals to the inner ear which may prompt reflex movement. 'The typical pulse rate of dance music is around the rate of locomotion,' he says. 'It's quite possible you're triggering a spinal reflex.'