For a glimmer of hope, he looked to a number of well-known musicians who arrived at their particular musical talent late in life—Patti Smith didn't consider becoming a professional singer until she was in her mid-twenties, iconic jazz guitarist Pat Martino only relearned to play after a brain aneurysm at the age of 35, and New Orleans keyboard legend Dr. John switched from guitar to piano when he was 21 after an injury, then won the first of his five Grammys at the age of 48. Having no such aspirations of grandeur, Marcus, aged 38 and with a documented lack of rhythm, still found himself desperately longing to learn to play the guitar. As he puts it, "Perhaps few people had less talent for music than I did, but few people wanted more badly to be able to play." So he confronted the fundamental question:

"Could persistence and a lifelong love of music overcome age and a lack of talent? And, for that matter, how did anyone of any age become musical?"

Curiously, one of the most influential experiments on critical periods comes from barn owls who, like bats, rely heavily on sound to navigate; but, unlike bats, they see better than bats do, and one of the first things they do after hatching is calibrating their ears with their eyes, attuning what they hear to what they see. But because this navigational mapping of auditory information depends on the exact distance between their eyes and ears, which changes as the owl grows, it can't be hardwired at birth.

To study how the owls calibrate their visual and auditory worlds, Stanford biologist Eric Knudsen devised a clever experiment, in which he raised owls in a kind of virtual reality world where prisms shifted everything by 23 degrees, forcing the owl to adjust its internal map of the world. Knudsen found that young owls learned to compensate for the distortion easily, and older owls could not—at least not in one go. But as soon as the 23 degrees were broken down in chunks—a few weeks at six degrees, another few at 11, and so forth—the adult owls were able to make the adjustment.

Using this insight, Marcus turned to David Mead's Crash Course: Acoustic Guitar, which broke guitar playing into the kind of bite-sized morsels fit for the human equivalent of adult owls. It gave Marcus the basics, and thus the first step in rewiring his own brain.

"This book is about how I began to distinguish my musical derriere from my musical elbow, but it's not just about me: it's also about the psychology and brain science of how anybody, of any age—toddler, teenager, or adult—can learn something as complicated as a musical instrument."