DESPITE LIVING in the Vienna of Mahler, Sigmund Freud was irritated by music. “Some rationalistic, or perhaps analytic, turn of mind in me rebels against being moved by a thing without knowing why I am thus affected and what it is that affects me,” he wrote — thus bizarrely turning his back on perhaps the most potent medium by which humans express their innermost feelings.

A century on, we are not much farther towards knowing why seemingly meaningless vibrations have such an effect on our mental state. But plenty of psychiatrists, psychoanalysts and neurologists have rushed in where Freud disdained to tread, and gathered evidence about music's impact on brains and behaviour. So Oliver Sacks isn't so much breaking new ground in Musicophilia as providing an elegant compendium of observations about mental disturbances triggered, fuelled, alleviated or cured by music.

His range is enormous, and the more admirable for being tackled (mostly) in layman's language. Here are tales of a man possessed with an insatiable desire to hear piano music after being struck by lightning, of another whose epileptic seizure created permanent music “playing” inside his head, of an eminent musicologist (the English conductor Clive Wearing) whose musical powers were unimpaired even though amnesia blotted out everything else, and of a severely retarded man able to recall hundreds of operas and play Debussy from ear after hearing it once.

But many stories will be familiar to all. He discusses how tunes go “round and round in the brain” and how, in some cases, they mushroom into musical hallucinations — often when a person has been deprived of receiving music (by, say, temporary deafness).

And he talks about music in dreams, citing his own experience of dreaming some anguished songs in German that he didn't recognise. When he hummed the tunes to a musical friend, they were identified as Mahler's Kindertotenlieder — Songs of Dead Children. And how did they get into Sacks's slumbers? Well, the previous day he had resigned his job in the children's unit of a hospital. Was this a troubled conscience speaking subliminally through music?

Modern scanning techniques reveal that musicians have different brains from the rest of humanity. Sacks discusses their remarkable gifts — notably what he calls “absolute pitch” (the mysterious ability, generally called “perfect pitch” in Britain, to name a musical note out of context). He doesn't explain it. Who can? But he does point out that half of all people born blind have it (among the general population the ratio is 1:10,000), which suggests that sensory deprivation in one area boosts perception in another.

Even more remarkably, perfect pitch occurs in 60 per cent of Chinese and Vietnamese music students, compared with only 14 per cent of American music students. Unlike English speakers, the Chinese and Vietnamese speak “tonal” languages, in which a word's pitch is critical to meaning. The much-disputed link between linguistic and musical skills is far more complex than many people believe. But Sacks, who provocatively (and wrongly) declares that music “lacks images, symbols, the stuff of language”, is probably not the right person to explore this.

What he does do, superbly, is survey the use of music as therapy. He looks at how singing can transform the brain's right hemisphere into an “efficient linguistic organ” when the left has been knocked out by a stroke; and how rhythmic music can “unlock” the movements of Parkinson's sufferers by imposing an external beat on their frozen inner clocks; and how, since musical memory seems to survive longer than any other kind, songs with autobiographical associations reawaken the “sense of self” in dementia sufferers.

All fascinating. But mostly it's about the “how” of music's relationship with the brain. What Sacks doesn't attempt is a grand theory telling us why. I don't blame him. The power of music remains as mysterious to us as it did to the Ancient Greek sailors lured on to the rocks by the Sirens' song. We can create it, enjoy it, exploit it, harness it. But we still can't explain it.

Musicophiia by Oliver Sacks
Picador, £9.99

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