This is the 11th collection of essays about medical anomalies by neurologist Oliver Sacks, and at 76, he's as cogent and elegant as ever. As the Time magazine reviewer remarked about an earlier book: "He has refined the case history into an art form." And he continues to do so without sacrificing the complexities and occasional unresolved questions arising from a medical predicament.

It is quite likely that what first sparked his interest in strange medical problems were his own. He cannot tell left from right; if he doesn't follow precisely the same route daily, he'll get lost. He cannot maneuver inside large buildings. And, more mysterious, he has prosopagnosia, the inability to recognize a face, even if he's just seen that person. Unlike the other conditions he describes, often the results of strokes, this one probably has a genetic basis, because it cannot be treated or improved.

It makes one wonder how it is that the majority of us get on in the world with largely unimpaired vision and brain function, when so much can be miswired or misfired. Take the tragically ironic story of Lilian in Sacks' opening piece, "Sight Reading." She was a brilliant pianist who gave concerts worldwide and taught master classes until what had for years been intermittent becomes horribly permanent: She loses the ability to read music. Over the next nine years she also loses words, cannot make out what the objects around her are (she can see but not understand or define). If she puts a bowl on a table and her husband moves it, she is unable to find it again. When Sacks last sees her, nothing has improved, but there's a lifetime of music inside her and she still plays brilliantly.

Another plucky example is that of the writer in "A Man of Letters," who awakes one morning after a series of small strokes and finds that his morning newspaper appears to be written in Cyrillic. He has lost the ability to read, though he can write as well as before. (But he can't read what he's written.) It's a condition called aphasia sine agraphia. He learns to cope by turning to audio books and dictation.

Despite all the ills that befall the subjects of these essays, this is an inspiring book. Human beings are adaptable and so, it turns out, is the brain. It remains plastic well into middle age. "One part or system of the brain may take over the functions of a defective or damaged one." This is in part because every module of the brain "must interact with dozens or hundreds of others, their total integration creating something like a vastly complicated orchestra with thousands of instruments." When one fails, another can step in.

Sacks raises a number of fascinating questions about vision, thinking, reading and writing. Can thinking, for example, be pure ideation, pre language or visual imagery? And how is it that our brains are wired for reading and writing? We've been talking since the dawn of humankind, but writing is only about 5,000 years old.

Darwin had a very "open view of the process of natural selection and adaptation, foreseeing that biological structures might find uses very different from those for which they had originally evolved."

There is much to ponder in this erudite yet lucid book, and Sacks shows us that despite the myriad of problems that can arise in the brain, it is a wondrous instrument.

Brigitte Frase is a writer and critic in Minneapolis.