Excerpt from How We Learn by Benedict Carey, plus links to reviews, author biography & more

Scientists had known since the nineteenth century that some skills, like language, are concentrated in specific brain regions. Yet those seemed to be exceptions. In the 1940s, the neuroscientist Karl Lashley showed that rats that learned to navigate a maze were largely unfazed when given surgical injuries in a variety of brain areas. If there was some single memory center, then at least one of those incisions should have caused severe deficits. Lashley concluded that virtually any area of the thinking brain was capable of supporting memory; if one area was injured, another could pick up the slack.

In the 1950s, however, this theory began to fall apart. Brain scientists began to discover, first, that developing nerve cells—baby neurons, so to speak—are coded to congregate in specific locations in the brain, as if preassigned a job. "You're a visual cell, go to the back of the brain." "You, over there, you're a motor neuron, go straight to the motor area." This discovery undermined the "interchangeable parts" hypothesis.

The knockout punch fell when an English psychologist named Brenda Milner met a Hartford, Connecticut, man named Henry Molaison. Molaison was a tinkerer and machine repairman who had trouble keeping a job because he suffered devastating seizures, as many as two or three a day, which came with little warning and often knocked him down, out cold. Life had become impossible to manage, a daily minefield. In 1953, at the age of twenty-seven, he arrived at the office of William Beecher Scoville, a neurosurgeon at Hartford Hospital, hoping for relief.

Molaison probably had a form of epilepsy, but he did not do well on antiseizure drugs, the only standard treatment available at the time. Scoville, a well-known and highly skilled surgeon, suspected that whatever their cause the seizures originated in the medial temporal lobes. Each of these lobes—there's one in each hemisphere, mirroring one another, like the core of a split apple—contains a structure called the hippocampus, which was implicated in many seizure disorders.

Scoville decided that the best option was to surgically remove from Molaison's brain two finger-shaped slivers of tissue, each including the hippocampus. It was a gamble; it was also an era when many doctors, Scoville prominent among them, considered brain surgery a promising treatment for a wide variety of mental disorders, including schizophrenia and severe depression. And sure enough, postop, Molaison had far fewer seizures.

He also lost his ability to form new memories.

Every time he had breakfast, every time he met a friend, every time he walked the dog in the park, it was as if he was doing so for the first time. He still had some memories from before the surgery, of his parents, his childhood home, of hikes in the woods as a kid. He had excellent short-term memory, the ability to keep a phone number or name in mind for thirty seconds or so by rehearsing it, and he could make small talk. He was as alert and sensitive as any other young man, despite his loss. Yet he could not hold a job and lived, more so than any mystic, in the moment.

Excerpted from How We Learn by Benedict Carey. Copyright © 2014 by Benedict Carey. Excerpted by permission of Random House, a division of Random House LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.