Why does music play such a large role in our lives? How can simply hearing even a snippet of a song trigger memories and emotions? Why do some songs have instant, almost universal appeal, while others require multiple hearings before we even begin to understand, much less enjoy, them? Finally, why is it that, try as we might, we can’t get that annoying jingle out of our heads?

“It’s because we’re all hardwired for music,” said Daniel J. Levitin when I spoke to him last week by phone from his home base at McGill University in Montreal. In his new book, This Is Your Brain on Music: The Science of a Human Obsession, this Bay Area native son combines his years of experience in the music business, his study of cognitive psychology, and references ranging from Bach to hip-hop to explain our love affair with music.

It would be hard to find a better guide. Levitin grew up playing saxophone and listening to classical music, jazz, and rock and roll. After almost receiving a degree from Stanford University in music and psychology (he left when told he couldn’t major in saxophone), he spent years in the commercial music world, where his engineering and musical skills took him from working as a session musician, live sound engineer, record producer, and consultant for numerous rock groups — including Santana, Steely Dan, and Stevie Wonder — to director and eventually president of artists and repertory for 415/Columbia Records. It was during this period that he first began wondering why some people seemingly had a gift for music, why the greats could hear nuances that most people couldn’t, and what role the human brain played in all of this.

He returned to Stanford in 1990 to get his B.A. in cognitive psychology and cognitive science while lecturing extensively in the music department on audio recording. He went on to earn his Ph.D. in psychology from the University of Oregon, researching absolute pitch in both musicians and nonmusicians. Today, as an associate professor of psychology, neuroscience, and music at McGill University, he runs the Levitin Laboratory for Musical Perception, Cognition, and Expertise, where he is still looking for better understanding of many of those same questions.

Add to this resume the skills of a gifted writer and a Web site that gives audio clips of the almost 200 songs he cites as examples, and the result is a book that resonates with musicians, scientists, and those of us who just like a good tune. Since its publication in August 2006, it has made news from Sweden to New Zealand. It is a New York Times bestseller, a Booksense bestseller, and has gone back to press 13 times. Levitin has been profiled in The New York Times, on The NewsHour with Jim Lehrer, and has even made the pages of People. The publishers just call it “The Little Book That Could.” Not bad for a 49-year-old ex-rock insider turned psychology professor who in his spare time plays in a campus band known as the Diminished Faculties.

The good news, according to Levitin, is that we are all music experts. We may not be performing at concerts, or even be able to rattle off the notes of the C major scale, but we know music. Experiments have shown that babies can recognize music that was played to them while they were still in the womb. By age 5, we can recognize specific songs, and more important, tell when a note or chord is wrong. When asked to sing a song we’ve heard, we reliably replicate the pitch and tempo, even if we aren’t trained musicians. When someone begins singing a song we know in what is a new key, which as Levitin points out is common with songs such as Happy Birthday, our minds instantly transpose the song to this new key and we join in the singing.

Even more amazingly, we can recognize different versions of the same song, something that even the most sophisticated computer program can’t yet do. When we hear a new version of something we’ve heard before, we “know” the song, despite changes in pitch, tempo, rhythm, timbre, and musical style. We also have an innate ability to instantly categorize music, placing it within a familiar framework even when we haven’t heard all of it. That’s how we mentally can appreciate new music that falls into familiar patterns, and also explains why the unexpected in a piece, such as the “Surprise" symphony by Haydn, can stimulate and delight us. In fact, we have the capacity to learn to enjoy any of the world’s musical styles, even if they differ substantially from the music we are familiar with.

But while the brain can be shown to give structure and order to the sounds we hear, it doesn’t completely explain why music affects us emotionally. As Levitin says in his book, “After all, we don’t get all weepy-eyed when we experience other kinds of structure in our lives, such as a balanced checkbook or the orderly arrangement of first-aid products in a drugstore (well, at least most of us don’t).”

This is where the “how” of how the brain processes music comes in. What was surprising to Levitin was just how many areas of your brain are involved in this process, whether you’re listening to, performing, or even mentally recalling music. “Conventional wisdom says brain functions are generally more localized, but music affects all areas,” he says. It is this complexity that allows music to affect us emotionally. It is the reason, Levitin argues, that music has played such an important role in our evolutionary development. And it is the reason music still continues to play such an important role in our lives.

So if we’re all musical experts, why aren’t we all performing musicians? Part of it is cultural — contemporary Western culture creates a divide between expert performers and the rest of us. But according to Levitin, the real difference is practice. Your piano teacher was right. He feels great musicians are made, not born. “If there were a musical gene, why don’t we hear about Mozart’s children?" he asks. "Professional musicians, even those who achieve acclaim as children, spend thousands of hours practicing, just as people do who are experts in any domain, such as a finish carpenter. When you read biographies of musicians we perceive as musical geniuses, no one ever says that it came easy.” While minor variations in our brains' neural setups may make it somewhat easier for certain people to master specific skills, it still requires time.

This Is Your Brain on Music is more than just an explanation of neurons and connections and their evolutionary importance. Levitin uses his almost encyclopedic knowledge of contemporary Western music to show how elements like timbre, pitch, and rhythm affect our perception. He says one of the most profound changes in Western music, starting with Ravel, is that composers have moved away from the rhythm-based compositions that had been the music’s driving force and now are using timbre as a focal point for composition. In his book, Levitin describes timbre as “that which distinguishes one instrument from another when both are playing the same wrtten note. It is a kind of tonal color that is produced in part by overtones from the instrument’s vibrations. ... The timbre of a sound is the principal feature that distinguishes the growl of a lion from the purr of a cat, the crack of thunder from the crash of ocean waves, the voice of a friend from that of a bill collector one is trying to dodge.”

He says that composers are now writing music with the overall sound in mind rather than for individual instruments, whether it’s a classical composition or classic rock and roll. “If I played 10 seconds of Mozart and 10 seconds of Haydn, you couldn’t tell them apart," Levitin said. "But if I play one-tenth of a second of Hendrix and one-tenth of a second of the Beatles, you instantly know which is which, even if you have no idea what the song is. That’s because of timbre.” We listen to music for its overall sound, not just for the specifics of an instrument or even the individual notes.

What’s also important to Levitin is how we learn to appreciate and understand new or “difficult” music, whether it’s an unfamiliar piece by a familiar composer or an entirely new genre. Until about age 20, we’re all open to learning new music, just as it’s fairly easy to learn a new language or the principles of mathematics, and it’s also when we’re more apt to experiment with new ideas and explore different cultures. Certainly, these are the years when many of us explore musical options. We never lose the ability to acquire new music, but after age 20, we’re primed by our brain’s synapses to stop making the new connections that speed our learning process. We start pruning out connections we don’t need.

But Levitin says, “It’s worth the effort to fight this tendency, especially with music." Take the time, he suggests, to listen to music that falls outside your familiar comfort zone. "I heard [Michael] Tilson Thomas conduct the Bartók Concerto for Strings and Orchestra. I hated it. So I went out and bought it, just to figure out why I hated it. Now, I love it.”

Levitin’s advice for understanding music of a different genre or style: Listen to something somewhat familiar, whether it’s a jazz standard or a classical chestnut, so you have a starting reference point. Listen in a nondistracting setting, such as while driving or at home or in your living room, and when you’re not involved in another intellectual activity, like reading. Finally, give yourself permission not to like everything. Not everyone has to like Schoenberg. As for Levitin’s own classical music preferences, he loves Debussy and Chopin, especially as interpreted by Aldo Ciccolini and Maurizio Pollini. His favorite pieces include the Brahms Fourth Symphony, Mahler's Fifth, Beethoven's Sixth, and Julia (Nine Pieces for Solo Piano) by Jon Appleton. He also likes Bizet, Poulenc, Boulez, and Rachmaninov. His choice for interpreting Beethoven sonatas is Rubenstein.

When it comes to classical music, though, Levitin does feel that contemporary classical composers aren’t reaching the same audiences as they used to. “One hundred years ago, Beethoven would compose something and orchestras would play it," Levitin says. "Now the major orchestras seldom play new contemporary classical pieces, unless you’re lucky enough to live near a university.” But where he does find contemporary classical music widely heard is in films. “People like John Williams and Hans Zimmer are composing contemporary pieces in the classical style.”

As for why we can’t get that jingle out of our head? It’s known as an ear worm. There’s been little research done, but the most likely explanation is that the neural circuits get “stuck.”

So far, says Levitin, there’s no cure.