We come to know our brains only when they fail us. We have a hard time believing that our every thought, inexplicable wish, or misguided remark — let alone our higher intellectual pursuits — originates in the pale, wrinkled organ between our ears, and the compilation we call our sense of self does not seem contained in the neat compartment of our skulls. But when things go wrong, it is hard to look past anatomy, or to get beyond the diminishing sense that our psychological lives are predicated on our biological ones.

Much of what is now known about the human brain comes from studies of brain injuries. In an 1861 autopsy of a patient who had lost the ability to speak after suffering a severe stroke, the French surgeon Paul Broca attributed the man’s disrupted speech to damaged tissue he found in the left frontal lobe. The discovery of “Broca’s area” not only localized the site of language production, it also provided early evidence for lateralization (a term applied to the cognitive functions, like speech, that are performed almost entirely by one hemisphere of the brain, rather than both). In the 1950s, surgeons removed both temporal lobes of the now-famous epilepsy patient H.M., leaving him without a hippocampus — and, his doctors discovered, without the ability to acquire new memories. As a result, we now know that the hippocampus plays a crucial role in the production of our own personal histories.

But while injury can make the brain more knowable, it can also render the victim less so. When we encounter a patient who has suffered a severe head trauma or stroke, we often feel a shiver of nonrecognition: The patient had led a normal, recognizable life, we know, compiling memories and experiences in the usual way, but the injuries have put an end to that particular story, and it takes a struggle to see the new protagonist as anything but less than fully human. He or she becomes unfamiliar, strangely unclassifiable; a shadow of a former life; a subject for anatomical inquiry, like a cadaver. As Michael Paul Mason points out in his illuminating “Head Cases: Stories of Brain Injury and Its Aftermath” (Farrar, Straus and Giroux, 320 pages, $25), in many cases of traumatic brain injury, patients get shuffled into psychiatric hospitals, mixed in alongside the mentally ill.

Mr. Mason’s book confronts this impulse to dismiss and dehumanize. He is a brain injury case manager, working as victims’ advocate in the struggle — often fruitless, always arduous — to get the brain-injured the medical care they need. He faces countless obstacles: the scarcity of treatment programs in this country, the inevitably staggering cost of treating a brain injury (on average, $4 million over a lifetime), and the number of people who have them. “In America alone, so many people become permanently disabled from a brain injury that each decade they could fill a city the size of Detroit,” he writes. “Seven of these cities are filled already. A third of their citizens are under fourteen years of age.”

So Mr. Mason travels back and forth across the country, meeting the people whose interests he will represent. “Head Cases” is a collection of their stories. There is Cheyenne Emerick, a man in his 40s, living, barely, in a dilapidated Hollywood apartment and suffering 120 seizures every month. We learn about his talent for acting, and his old passion for snowboarding, which took him to the famed Utah ski run where he went off a precipice at top speed, lost sight of where the sky turned back into the ground, and landed awkwardly, his knee slamming into his head and sending his brain into a ricochet against the walls of his skull.

There is Julie Meyer, who lost her memory after a car accident, and is now “a prisoner of the present.” Without the ability to recall anything further back than a minute or two, she has become a “perfect mirror” of the people she encounters, instantly taking on whatever emotion they express, laughing when they laugh, raging when they are angry. There’s a man who, after a herpes infection spreads to his brain, regularly becomes convinced that he’s dead; there’s a 25-year-old woman with two master’s degrees, a doctorate in math, and a career as an artist despite, or perhaps because of, the massive brain injury she suffered at 12 when she flew over her bicycle’s handlebars.

In these cases, and several others like them, Mr. Mason’s accomplishment is formidable, restoring to each subject a measure of human dignity, achieving through sympathy and curiosity insight like that which pulses through genuine literature. These are not people whose lives have ended, he suggests, only changed, and we recognize in their jagged, altered lives something like allegories for our own experience. But this is not mere literary conceit, and Mr. Mason’s approach has parallels within current scientific research: Mark Solms, the co-director of the International Neuropsychoanalysis Centre, has recently established the unprecedented practice of putting brain injury patients in psychoanalysis, hoping to achieve a richer sense of what each injury means, subjectively, for each patient.

At times, however, the tone of “Head Cases” turns naive and boastful, as Mr. Mason excoriates the callous behavior of neurosurgeons (forever “rolling their eyes,” he tells us, in the face of their patients’ distress) and the hapless work of psychiatrists, implying that he, unlike them, is in touch with the larger truth here, the greater humanity. In these moments, his book resembles an ugly and unsubtle crusade, but, taken whole, its contents constitute instead a modest corrective — to the narrow medicalization of brain injuries, as well as to the belief that a damaged brain is a defining destiny.

Ms. Schwartz is a graduate student in neuropsychoanalysis at Yale University. She last wrote for these pages on Susan Pinker and gender difference.