A surgeon in his 50s suffers an incapacitating stroke. He is one of the first patients to enroll in a rehabilitation clinic guided by principles of neuroplasticity: his good arm and hand are immobilized, and he is set cleaning tables. At first the task is impossible, then slowly the bad arm remembers its skills. He learns to write again, he plays tennis again: the functions of the brain areas killed in the stroke have transferred themselves to healthy regions.

An amputee has a bizarre itch in his missing hand: unscratchable, it torments him. A neuroscientist finds that the brain cells that once received input from the hand are now devoted to the man’s face; a good scratch on the cheek relieves the itch. Another amputee has 10 years of excruciating “phantom” pain in his missing elbow. When he puts his good arm into a box lined with mirrors he seems to recognize his missing arm, and he can finally stretch the cramped elbow out. Within a month his brain reorganizes its damaged circuits, and the illusion of the arm and its pain vanish.

Research into the malleability of the normal brain has been no less amazing. Subjects who learn to play a sequence of notes on the piano develop characteristic changes in the brain’s electric activity; when other subjects sit in front of a piano and just think about playing the same notes, the same changes occur. It is the virtual made real, a solid quantification of the power of thought.

From this still relatively primitive experimental data, theories can be constructed for the entirety of human experience: creativity and love, addiction and obsession, anger and grief — all, presumably, are the products of distinct electrical associations that may be manipulated by the brain itself, and by the brains of others, for better or worse.

For neuroplasticity may prove a curse as well. The brain can think itself into ruts, with electrical habits as difficult to eradicate as if it were, in fact, the immutable machine of yore. Sometimes “roadblocks” can be created to help steer its activity back in the desired direction (like bandaging the stroke patient’s good arm). Sometimes rewiring the circuits requires hard cerebral work instead; Dr. Doidge cites the successful Freudian analysis of one of his patients.

And, of course, the implications for external re-engineering of the human brain are ominous, for if the brain is malleable it is also endlessly vulnerable, not only to its own mistakes but also to the ambitions and excesses of others, whether they are misguided parents, well-meaning cultural trendsetters or despotic national leaders.

The new science of the brain may still be in its infancy, but already, as Dr. Doidge makes quite clear, the scientific minds are leaping ahead.