The loss of a gracious man who taught us about the loss of memory.

Last Tuesday evening marked the death of a very strange, very impaired, and very important man. Despite his worldwide fame, almost no one knew his name until now, yet the world owes him a debt it can never repay.

He was Henry Gustav Molaison, known only as H.M., initials that became a household word throughout brain science. He was born in Louisiana and grew normally until he was nine, when a severe bicycle accident began a new phase of his life. 

He had seizures during those years; they first involved only transient mental changes, but progressed to blackouts and then in early adulthood to full-blown convulsions that became more and more frequent. He could no longer work at his job repairing motors, and he was increasingly impaired.

At the age of 27, in 1953, he went to see neurosurgeon William Scoville who, after trying other treatments, did radical brain surgery. It is not unusual for surgery to be done for intractable and disabling epilepsy. The goal is to remove the piece of brain that contains the seizure focus, and it often works. But in this case Scoville boldly—much too boldly it turned out—removed a large part of the temporal lobes on both sides of Henry Molaison's brain.

If you hold your hands palms upward in front of you and cup them together as if to hold water, and then let the tips of your thumbs almost touch, you have a passable, life-size, upside-down, three-dimensional model of your brain. If this were Henry Molaison's brain, the thumbs would be missing up to the second joint.

No one anticipated the result of this drastic surgery, but it was devastating. Molaison lost the ability to store new memories in his brain, a condition called anterograde, or forward-going, amnesia. This means his doctors and nurses, everyone he would meet after his loss, would have to reintroduce themselves each time they entered his room. And he would be unable to recall any event occurring during the 55 more years that he lived.

Fortunately, he was able to recall most important things and people from his childhood, and many events up to three or four days before the surgery. His speech and many other mental abilities were normal. But he was never again able to live independently.

Over the years gifted neuropsychologists, especially Brenda Milner and later Suzanne Corkin, studied him intensely—or you might say, studied with him—and learned an enormous amount about human memory. It turned out that what H.M. lost was "only" what is now called declarative memory.

Like his childhood memories, his short-term memory, which we use to remember a phone number long enough to write it down, and which is critical to ongoing tasks including thought, was intact. Also, his procedural memory, which helps us get better at tasks as we repeat them again and again, worked quite well.

For example, he rose to the challenge of learning to draw by looking at the figure and his hand only in a mirror. This is not easy, but he became good at it, although each time he practiced he thought it was something new, and at one point remarked that he was surprised he could do it so well.

Thanks to Henry Molaison, we now know that these different kinds of remembering are in part carried out by different circuits in the brain. Going back to the cupped hands model, your thumbs contain the hippocampus and nearby parts of the cerebral cortex in the temporal lobe.

When you meet someone new, the sights and sounds of that person are processed in many parts of the brain, but if you are to remember the meeting, the face, and the voice, those perceptions must converge on the temporal lobe and then pour into the hippocampus; as the hippocampus processes them and reports its results into the emotional core of the brain, you form a memory. It's something like pressing the "Save" button on your computer, although it can take a day or more.

We also know that short-term memory depends on parts of the frontal lobe—the backs of your fingers in the upside-down model—while the gradual learning of a practiced task is distributed over all the circuits that are repeatedly fired, and involves stable changes in the chemistry and even the microscopic structure of brain cells.

After Henry Molaison's death, the president of the Society for Neuroscience said, "What H. M. lost, we now know, was a critical part of his identity." Yes and no. 

It might be more accurate to say that he lost the ability to build and change his identity with experience as he aged. When he died, he did not have the identity of an 82-year-old. But he still had the identity he had when he was 27, including his memories of childhood and early life, and the relationships he had with family and friends before his loss.

Famed neurologist and writer Oliver Sacks described a similar patient named Jimmy, who in the 1970s still thought of himself as a 20-year-old navy soldier at the end of World War II. In a little experiment Sacks later felt guilty about, he had Jimmy study his face in a mirror; Jimmy was briefly upset by the older man he saw there, but of course, he soon forgot the incident.

Like Jimmy, H.M. still had his personality; Brenda Milner described him as gracious and very patient with all the tests she engaged him with, although he blushed once when a visiting doctor referred to him in his presence as "an interesting case." He had a mild awareness of his importance, because of the hubbub that sometimes surrounded him. And his brain itself will now be intensively studied, greatly increasing the value of all we know about his mind.

A few years ago, the film Memento premised a mystery story on a case that was purportedly like H.M. But the protagonist functioned far too well in the world to really have been such a patient. The loss that H.M. suffered, the ability to store new memories, was a very severe one, and his life was limited to his parents' home and after their deaths to a nursing home.

Yet because of his grace and patience, his great loss became brain science's great gain, and we can all remember him with gratitude.