My cat has exquisitely sensitive hearing, but music interests her not at all. She greets simple folk music, sublime Bach fugues, and complex African polyrhythms with the same regal indifference. Yet let her hear the faintest hint of a can opener and her ears will perk up. She'll race to her bowl. Music certainly hath not charms to soothe the savage beast.

But music's charms do soothe the savage breast, which is closer to the original version of William Congreve's quote. As far as is known, music has been an important part of every human society from the most primitive and "savage" to the most modern and civilized. What is it about the human brain that allows music to engage us so profoundly? That is the central question that pianist, composer, and technical writer Robert Jourdain attempts to answer in Music, the Brain, and Ecstasy.

Jourdain sets the stage with a lucid discussion of how our ears and our brains perceive sound. He argues that of all the senses, hearing is the most "difficult," a "late bloomer" in evolutionary terms, because of its reliance on fragile mechanical structures.

The author continues with fascinating disquisitions on the nature of melody, harmony and rhythm, the basic elements of music. As an aspiring percussionist, I was particularly fascinated by the interplay between melody and rhythm. Jourdain points out that a melody will become unrecognizable when its rhythmic structure is altered only slightly, by shifting it across bar lines by a single beat, so that the accents fall on different notes. On the other hand, try tapping out the rhythm of a well-known melody, such as "Mary Had a Little Lamb." Practically anyone can identify the song by its rhythm alone, without any tonal information.

Nevertheless Jourdain successfully demolishes the notion, beloved by percussionists, that rhythm is the most essential aspect of music, instilled in utero by the beating of our mother's heart. He believes that melody is primary. Melody is based on tones, which are organized into scales, The book contains an evenhanded discussion of the relative value of Western and non-western scales. According to the author, some aspects of scales are determined by the way our brains perceive sound. Others are biologically based but not hardwired, and still others are matters of historical happenstance.

Jourdain offers a commendably nuanced discussion of brain lateralization as it pertains to music. Too many such discussions in works intended for the general public stop at the Sunday supplement notion that the left brain is logical and analytical and the right brain is intuitive and holistic. Jourdain avoids that trap. For example, he notes that the left ear (which primarily feeds the right hemisphere) is better at identifying melodies than the right ear (which primarily feeds the left hemisphere). So melody is a right-brain function, correct? Not so fast. This is true only in the musically unskilled.

The first half of the book contains a great deal of elementary information both about how the brain perceives sound and about the elements of music. Experienced neuroscientists and musicians may be tempted to skip these discussions, but if they do they'll be denying themselves some of the pleasure of Jourdain's lyrical and graceful writing style. Consider this passage, in which Jourdain vividly describes the complex interplay between the body and various brain systems as a pianist plays a piece of chamber music.

After excellent discussions of how the brain perceives melody, harmony, and rhythm, with numerous examples from popular and classical music, Jourdain considers the question of whether musical inventiveness has reached a kind of dead end. He argues that by the beginning of the Twentieth Century composers had thoroughly explored most available melodic and harmonic relationships. With that territory mapped so well, serious composers of modern music have been striking out into new areas, writing in strange, dissonant scales, with unsettling melodic structures and unfathomable rhythms. They may have gone so far beyond the brain's ability to comprehend such structures that the result can hardly be called music. This can't continue. "In the name of self improvement," writes Jourdain, "today's symphony audiences sometimes sit through premiers of contemporary works they can hardly stomach, suffering harmonies that sound consistently dissonant, rhythms without apparent pattern, and a dearth of melody. To this the public responds with remarkable passivity, applauding politely to celebrate the end of their suffering."

Despite the book's fascinating facts and elegant writing, it has problems. Music, the Brain, and Ecstasy seems inadequately researched, and it's certainly inadequately referenced. Chapters dense with information contain mere handfuls of endnotes, most referring only to secondary sources such as textbooks. In fact, Jourdain's bibliography consists exclusively of books, with not a single reference to an individual, peer-reviewed, journal article. To take just one example among many, in a discussion of how listeners focus their attention Jourdain writes, "We attend most intently to melody at the peaks and valleys of its contour, most intently to harmony at crucial shifts of key, most intently to rhythm when metrical patterns are violated or when phrases begin or end." Now this is a fascinating series of assertions. Although they ring true, Jourdain provides not a whit of evidence for them in the text or in his endnotes, leaving the reader no opportunity to follow up with the original literature.

In the end this is a crucial omission that is especially disappointing to Jourdain's most attentive readers. How much of this book is science and how much consists of Jourdain's opinions and educated guesses? A curious reader will never know.

Despite such frustrations, Music, the Brain, and Ecstasy is well worth the attention of music lovers who wish to know more about the brain, and neuroscientists who wish to learn more about this uniquely human cognitive function.