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THE SEA MONSTER

Or: The discovery of the hippocampus

Your memory is a monster; you forget—it doesn’t. It simply files things away. It keeps things for you, or hides things from you—and summons them to your recall with a will of its own. You think you have a memory; but it has you!

JOHN IRVING, A Prayer for Owen Meany

AT THE BOTTOM of the ocean, tail curled around seagrass, the male seahorse sways back and forth in the current. He may be tiny and mysterious, but no ocean creature compares to him. The only male in the animal kingdom to become pregnant, he stands on guard, carrying his eggs in his pouch until they hatch and the fry swim away into the open sea.

But let’s back up: this isn’t a book about seahorses. To find our real subject, we must rise out of the depths and journey back 450 years.

The year is 1564. We’re in Bologna, Italy, a city full of elegant brick buildings and shady, vine-covered walkways. Here, at the world’s first proper university, Dr. Julius Caesar Arantius bends over a beautiful object. Well, beautiful might be an exaggeration, if you’re not already deeply, passionately involved in its study. It’s a human brain. Rather gray and unassuming, and on loan from a nearby mortuary. Students surround the doctor, clustered on benches throughout the theater, following his work intently, as though he and the organ in front of him are the two leads in a drama. Arantius leans over the brain and slices through its outer layers, studying each fraction of an inch with extreme interest, hoping to understand what it does. His disregard for religious authority is clear in the gusto with which he approaches his dissection because, until shortly before that time, the scientific study of human corpses had been strictly forbidden.

The doctor cuts further into the object, examining what’s inside. And then, deep within the brain, buried in the temporal lobe, he finds something very interesting. Something small, curled up into itself. It looks, he thinks, a bit like a silkworm. The upper classes of the Italian Renaissance loved silk, a luxurious and exotic fabric that arrived in Venice via the Silk Road from China; by extension, they loved silkworms too. Intrigued, Arantius looks closer, making some careful cuts, and pries the little worm loose, liberating it from the rest of the brain.

This is the moment at which modern memory research was born, the precise moment that memory, as a concept, moved from the mythological world into the physical one. However, back then, on that particular day in sixteenth-century Bologna, life goes on in the markets as usual; people carry wine and truffles and pasta below the city’s famous pergolas and ancient red brick towers, oblivious to the hugely important discovery in their midst.

Arantius turns over what he has dug out of the brain and places it on the table before him, considering what it might be. That’s it! Rather than a silkworm, perhaps it is a tiny seahorse? Yes, indeed. With its head nodding forward and its tail curling up, it does look like a seahorse, the tiny distinctive fish living in shallow ocean waters between the tropics and England. And so he names it: hippocampus, meaning “horse sea monster” in Latin. It also shares its name with a mythological creature—half horse, half fish—said to wreak havoc in the waters around ancient Greece.

By the light of a tallow candle perched on an autopsy table, Julius Caesar Arantius couldn’t tell what this little part of the brain actually did. All he could do was give it a name. Hundreds of years passed before we fully understood the significance of what this Italian doctor held in his hands, and you might guess that it has something to do with memory. After all, memory is the subject of this book.

The world beneath the sea and the one in our brain are profoundly different, of course, but there are many similarities between the seahorse and the hippocampus. Just as the male seahorse carries his eggs in his pouch until it’s safe for the fry to be on their own, the seahorse of the brain also carries something: our memories. It watches over them and nurtures them until they are strong enough to make it on their own. The hippocampus is the womb that carries our memories.

No one knew how crucial the hippocampus was to memory until 1953, but there was endless speculation about where memories were stored in the brain. One popular early belief was that our thoughts flowed through the liquid inside our skulls, but that theory was long gone by 1953. By then, the prevailing thought was that memories were created and stored throughout the brain. But then something happened to sink this theory once and for all, an incident that was tragic for one man, fortunate for the rest of us. An unsuccessful experimental surgery was the key to understanding Julius Caesar Arantius’s earlier discovery.

IF HENRY MOLAISON had lived in modern times, his treatment would have been very different. Henry suffered from severe epilepsy, and several times a day—or sometimes several times an hour—he had small absence seizures (also known as petit mal seizures), in which he would black out for a few seconds at a time. At least once a week he’d suffer a major convulsive seizure (or a grand mal seizure), in which he’d completely lose consciousness and his body would shake violently for several minutes. The medicines he was prescribed only made things worse and resulted in more seizures. In 1953, at age twenty-seven, he sought treatment from a surgeon, William Beecher Scoville, who proposed an operation unthinkable by today’s standards.

Dr. Scoville didn’t have the benefit of hindsight. He was inspired by reports of a Canadian surgeon who’d removed the hippocampus on one side in several patients in order to cure their epilepsy, and he believed that if he removed the hippocampi from both sides of Henry’s brain, then the treatment would be twice as effective. Henry listened to his doctor. After a lifetime of crippling epilepsy, he was desperate, and he agreed to the operation. Unwittingly, Henry Molaison had signed up to become the most important subject in the history of memory research.

When Henry woke up after the surgery, doctors found that he had no memory of the last two or three years; in fact, he couldn’t retain anything beyond what was present within his short-term memory. The nurses had to show him the way to the bathroom every time he needed to go. He had to be constantly reminded of where he was, because he forgot as soon as he thought of something else. He had lost his ability to form new memories.

For the remaining fifty-five years of his life, Henry lived literally in the moment. He couldn’t remember what he’d done half an hour ago, or the joke he’d told a minute earlier. He couldn’t remember what he’d eaten for lunch and had no idea how old he really was, until he looked in the mirror and saw gray hairs. He had to guess what season it was when looking out the window. Since he couldn’t remember new information, he couldn’t manage his money, diet, or household chores, so he lived at home with his parents. In spite of this, he was usually calm and content. But sometimes, things would upset him—like the death of his father.

Each morning, Henry woke up with no recollection of his grief, but every time he rose, he made an alarming discovery: the valuable weapons collection normally hanging on the wall was missing. He understood there was something wrong—the weapons were gone—and concluded that the house had been burgled and the weapons stolen. The truth was that his uncle had inherited the collection. But there was no use explaining that this was due to his father’s death, as the next morning he would conclude, all over again, that he’d been burgled. Finally, his uncle had to return the weapons collection. Eventually, Henry appeared to get used to the fact that his father didn’t come home anymore and, to some degree, understood that he was gone.

Scoville’s surgery on Henry was an experiment, but no one at the time could have anticipated the consequences. In fact, Scoville had already performed the operation on dozens of other patients. None had shown any obvious signs of memory loss. But there was a catch: every patient in this group had been acutely schizophrenic, paranoid, or psychotic. Their behavior was already abnormal, so any memory problems were blamed on their psychosis. Incidentally, they were no less schizophrenic after the surgery. But this was the era when lobotomies were in fashion, and Scoville believed he could improve this procedure by removing the hippocampi rather than following the classic approach of removing parts of the brain’s frontal lobe. Exactly why he believed this is another story. Our story centers on the consequences of his famous surgery on Henry Molaison. But there were also consequences for Scoville, who was deeply concerned about the results of the surgery. In a scientific paper he cowrote with Canadian neuropsychologist Brenda Milner in 1957, he confessed to his mistake. In the years after the article was published, Milner endeavored to find out more about how Henry’s memory was damaged. She believed that together, she and Henry would be able to explain to the world how human memory functions.

What could be learned about memory by studying Henry Molaison? Simply talking to him revealed some basics about the structure of memory; he was quite capable of sticking to the topic of conversation, as long as his thoughts didn’t wander and he didn’t become distracted by something around him. This meant that he had normal short-term memory. Short-term memory is what we remember in the moment. Before our experiences become permanent memories, they spend time in short-term memory. When we look up a phone number, we remember the number for a short while before we dial it. The same happens when we learn a new word or somebody’s name. These things remain in our memories for no more than a few seconds, or as long as we keep thinking about them. Sometimes, items that pass through short-term memory are picked up for long-term storing. In this case, all that remained was Henry’s short-term memory, but he learned how to use it in ingenious ways. During one study, examining his ability to perceive time, a researcher told him that she would leave the room, and that when she returned, she would ask him how long he thought she’d been gone. He suspected that he wouldn’t be able to do this, so he did something clever; he looked at the wall clock (something the researcher hadn’t noticed) and memorized the time by silently repeating it to himself, over and over again, until she returned. When she came back, he looked at the clock again to calculate how long she’d been gone. Since he’d focused on this one task during the test, he was able to keep the information in his short-term memory. Henry knew that he was participating in an experiment. But he couldn’t remember the researcher or her name.

Luckily, Henry enjoyed mental challenges; he always had a crossword with him and happily solved puzzles, which made him a willing participant in Brenda Milner’s experiments. In one example, she gave him a small maze, in which he had to negotiate steps through a grid to find an exit. After 226 attempts, he still couldn’t do it. But since he had no recollection of all his previous attempts, he happily carried on trying.

Another time, Milner asked him to draw a star while looking only at a reflection of his hand in a mirror. For anyone, this is a difficult task, because when you’re watching a mirror image, you tend to move the pencil in the wrong direction when you get to a corner of the star. But with practice you can improve. It’s a way of learning, of remembering, that helps you perform a task better the next time. But unlike remembering events you have experienced, or figuring out a maze, this kind of memory doesn’t involve conscious thought. It’s like riding a bicycle; you never remember that you have to move your feet a certain way, or tilt your body to keep your balance; it becomes second nature. Each time Henry repeated the mirror drawing task, he too improved. As with people with intact hippocampi, he eventually mastered the mirror star test. His final, almost perfectly drawn star surprised him, because he had no knowledge of the previous attempts that had helped him to gradually improve.

“That’s strange. I thought it would be difficult, but it looks as though I’ve done it rather well,” he said, astounded.

Brenda Milner was also astounded. She’d made a crucial discovery about long-term memory: that it consists of different, separate storage areas. In learning tasks that are not based on conscious memories, but rather on procedural memories (the body’s memory of how to do something), the hippocampus is not involved. If it were, Henry wouldn’t have done so well.

IN LATER YEARS, Suzanne Corkin, a student of Brenda Milner’s who became a neuroscientist, took over the work of researching Henry Molaison’s memory. Corkin and Henry’s partnership lasted for more than forty years, and in a way continued past his death. But though the two saw each other frequently, and to her he was like an old friend, she was new to him every time they met. When she asked him if he knew who she was, he replied that there was something familiar about her. He would guess that she was perhaps an old schoolmate. He may have wanted to be polite, but perhaps there was a remnant of something like a memory in his brain, which gave him a feeling of recognition, without knowing where it came from.

Henry reaffirmed that we possess a short-term memory, something he still had, and a long-term memory, which he had only half of—the part involving unconscious learning, otherwise known as procedural memory. What he was missing was the ability to store memories that can be consciously recalled: facts about the world and himself, called semantic memories, and all the experiences that would normally become part of his personal memory album, called episodic memories.

The modern theory of memory—based in part on Henry Molaison—suggests that previously stored memories are separate from new memories waiting to be let in. Henry did have memories from before his surgery. He remembered who he was and where he came from. He remembered events from his childhood and youth. But the three years leading up to the surgery were completely gone. This meant that memories could not be stored in the hippocampus, or at least not only there. Anyway, it is unlikely that there could be room for all of life’s experiences in such a tiny, fragile structure deep inside our brain. The role of the hippocampus must be to hold on to memories while they are maturing, before they are properly stored elsewhere in the brain—in the cerebral cortex, the outer layer enveloping the brain. It’s logical to think this process may take about three years, since Henry couldn’t remember the three years prior to his unfortunate surgery.

As Henry was living life from one minute to the next, in the safety of his mother’s house, the continual experiments turned him into something of a memory celebrity. Fortunately, researchers kept his identity hidden until after his death. If they hadn’t, he would have been vulnerable to overenthusiastic researchers and journalists. He was known only by his initials, and to this day, memory researchers around the world refer to him only as H.M.

Henry contributed his life to research—or at least the memories of his life. He took part in one experiment after the other, so researchers could document how memory works. Although he remembered very little after the surgery, he had memories of conversations with his doctor from several years prior to the surgery. This meant he understood that something had gone wrong—maybe with the surgery. This is why he repeatedly told the researchers that he wanted to help prevent the same thing from happening to others. “It’s a funny thing—you just live and learn. I’m living, and you’re learning,” he said.

Another important consequence of the research on Henry was that no one was ever operated on in the same way again. Scoville quit removing both hippocampi from his patients, whether they suffered from epilepsy or schizophrenia. Surgery to cure epilepsy did continue, however, and is still carried out today. If a patient has a certain type of epilepsy, originating in the area of the hippocampus, it can sometimes be remedied by removing one of the seahorses. The other one is left intact, so new memories still have at least one entrance into long-term memory.

For those of us whose brains are pretty much intact, it’s easy to take memory for granted. It’s easy to think, “I’m sure I’ll remember this, I won’t need to write it down.” All the special moments in our lives will remain with us as memories, won’t they? We like to imagine memory as a hard drive filled with film clips from our lives that we can watch whenever we want to. That’s not how it works, though. When we’re driving to the store or sitting around the dinner table with good friends and family, how can we be sure those precise moments will be remembered? Will those memories be useful or important in the future? Our memories do take good care of certain moments, of course: birthdays, weddings, a first kiss, the first time we score in soccer. But all the other moments—what happens to them? We spring-clean our brains now and then, throw out the clutter, and keep some things for safekeeping. This is a good thing, because if we had to remember every single moment of our lives, we wouldn’t be able to do much more than reminisce. When would we have time to live?

Some of us, however, store more than others: meet Solomon, the man who was unable to forget anything at all!

Solomon Shereshevsky worked as a Russian newspaper journalist in the 1920s. There, he annoyed his editor by never taking notes when he was given an assignment. The editor distributed the stories for the day, and while the other reporters eagerly wrote down what they needed to know to get to work, Solomon just sat there, as if he couldn’t care less.

“Haven’t you got anything of what I said?” the chief editor would ask.

But Solomon had gotten all of it: every address mentioned, every name, what the issue was. He could repeat it all back to his editor, every last detail. “Isn’t this the way it is for everyone?” he thought. He found it odd that others had to take notes. To him, it was natural that everything he heard, he remembered. Solomon’s editor sent him to see an expert. In the office of neuropsychologist Alexander Luria, Solomon was—like Henry Molaison—exposed to a battery of tests. How much was it possible for a human being to remember?

An almost limitless amount, as it turned out. At least it was difficult to find limits for Solomon’s memory. The psychologist showed him long lists of nonsense words and he could regurgitate them in perfect order, even backward and diagonally. He memorized poetry in other languages, tables of numbers, and advanced math in the blink of an eye. When Solomon met Luria again, seventeen years later, he could still repeat the same lists he had seen that time many years ago.

Solomon eventually quit his job at the newspaper and launched a new career as a mnemonist, a memory artist. He appeared onstage and memorized endless lists of numbers or words provided by the audience. Then he repeated them perfectly, to everyone’s amazement. But contrary to what you may think, an amazing memory—the kind so good we dream of having it ourselves—didn’t make Solomon rich, nor did it make him powerful or particularly happy. He jumped from job to job and finally died alone in 1958, without friends or family by his side.

Solomon Shereshevsky’s astonishing memory was partly due to something called synesthesia. This is a condition in which all sensations are accompanied by another sensation, such as sight, sound, smell, or taste. Solomon suffered from an extreme form of synesthesia. Everything he experienced was accompanied by impressions of bright colors, strong tastes, or special images. Hearing certain words would conjure distinct pictures, even tastes and smells. Certain voices evoked strong visual impressions. Once, when he was buying an ice cream at a kiosk, he recoiled in disgust because the seller’s voice made him see a billowing storm of black coal and ashes. These profound sensations made his memories latch on far stronger than a regular person’s. It was said that he couldn’t get rid of a memory—not even a meaningless list of numbers—unless he made a conscious effort to remove it.

Solomon was special. Almost no one remembers things as well as he did. Compared with his, the memory of an average person is a mere joke. But would you really want to be able to remember not only your parents’ phone number and the bus schedule from elementary school, but all phone numbers and bus schedules you have ever encountered?

Exactly fifty years after Solomon passed away, eighty-two-year-old Henry Molaison also died. The difference between these two exceptional men is not only that one of them had a vast trove of memories while the other couldn’t remember a thing. The fifty years between them also made a difference in terms of how their memories were researched. While we know a lot about Henry’s brain, we know nothing about Solomon’s. We don’t know if he had an extra large—or in any other way different—hippocampus. Meanwhile, Henry Molaison is still, even after his death, contributing to science. In his will, he bequeathed his brain to research, and the researcher who worked most closely with him for the last forty years of his life, neuroscientist Suzanne Corkin, planned to give her subject an afterlife in her field. After Henry’s death on December 2, 2008, Corkin worked together with a large team of physicians and researchers to make his brain work for posterity. First, researchers at Harvard scanned the brain with a magnetic resonance imaging (MRI) machine in Boston. Then, Corkin placed Henry’s brain in a cooler and handed it over to brain researcher Jacopo Annese, who took it on a plane bound for San Diego. Annese’s Brain Observatory stores the donated brains of deceased people so they can be used in various avenues of research, including on Alzheimer’s and normal aging. There, Annese’s team was ready and waiting to cut Henry’s brain into slices, thin as strands of hair. “We believe that the enormous attention that was devoted to patient H.M. when he was living and generously served as a keen research subject ought to be matched by a similarly involved study of his brain,” Jacopo Annese said.

Henry’s brain needed special attention. No other brain at the Brain Observatory had received as much scientific attention as his. The team photographed every single one of the 2,401 slices of Henry’s brain and stored them both in formaldehyde and as digital files. They spent fifty-three hours doing so, and Annese didn’t sleep until he was sure that all the pieces of this exceptional brain were securely preserved. Thanks to his work, researchers can now study the exact location where Scoville made his mistake and speculate about which of the remaining areas, near the hippocampus, helped Henry remember the few things which he occasionally and surprisingly did remember. In May 2016, Corkin passed away at age seventy-nine, and her brain is now in the safekeeping of other brain researchers. It contains no unusual surgical scars but houses decades of memories of her special contributions to research.

Henry Molaison’s legacy was an entirely new field of research. Now the hippocampus has a definite place in our memory. And during the past fifty years, memory research has become more and more focused on mapping memories all the way down to the cellular level.

“I believe that we will achieve the goal of explaining memory in the brain within my lifetime,” says one of the leading memory researchers in the world, Eleanor Maguire, professor at University College London and Wellcome Trust Centre for Neuroimaging. Her research, which focuses on the hippocampus, has allowed her to “see” memories. In one experiment, she told test subjects to think of a certain memory while she watched, through an MRI machine, the patterns that lit up their hippocampus. When they thought of other specific memories, different patterns became visible.

“Your experiences are taken into the brain. After that, the experience is taken apart and stored away in little pieces in the brain’s neocortex. Every time you recollect it, it is brought back to life. The hippocampus is critical to reconstructing the memory in your mind’s eye, enabling you to relive it once more,” says Maguire.

Memory research is also, in a sense, a process whereby small pieces are assembled into a larger puzzle. Memories cannot be seen, per se. No one can retrieve a memory and put it under the microscope. That’s also why it took so long for memory to move from being strictly a philosophical and literary topic to being the object of scientific examination. Psychology is a relatively new academic discipline, and so the scientific study of memory has a shorter history than that of many other subjects. But when memory researchers started piecing together human memory, they gave us a picture of an amazing inner world. They worked tirelessly with lists of words, meaningless shapes, staged bank robberies, life stories, puppet shows, and strings of numbers, all to reveal the truth about memory by using the brains of the people who volunteered to be guinea pigs.

Some of you will probably argue that it’s meaningless to measure something so abstract, a thing that exists only for the individual who owns the memory. How will we be able to reduce the evocative descriptions of memories in Marcel Proust’s seven volumes of In Search of Lost Time into figures and scientific graphs?

To capture unique human experiences and turn them into science, isn’t that a paradox? Like putting a seahorse in a glass of formaldehyde hoping to preserve its beauty and essence forever?

There are, however, many good arguments for why memory research is necessary. Turning memory into something concrete and measurable helps us compare memory in the healthy and in those with diseases, and it can help people with memory problems. It contributes to our understanding of how the brain works, which in turn may help find the solution to major medical issues of our time, such as Alzheimer’s, epilepsy, and depression.

Some 140 years of measuring memory has not solved all its riddles—far from it. Disagreements come and go on the memory battleground. One longstanding dispute is referred to as the “memory wars.” One side maintains that, in extreme situations, memory will behave differently, producing things like repression and dissociation. The other side maintains that memory always behaves the same way, only much more strongly in extreme situations. Another hot issue is the possibility of memory training: Is it like strengthening a muscle—that is, it gets better with repetition—or can you use strategies and techniques to improve existing ability? And what exactly is memory? Even this is being debated in minute, technical detail in scientific papers—debates punctuated by indignant letters to the editors of scientific journals—while researchers try to gain ground in the scientific community. It’s almost like an election campaign in slow motion, or a TV debate spread out over fifty or a hundred years.

There’s even discord over the hippocampus. Two camps face each other. One rigidly believes that the role of the hippocampus is simply to consolidate memories into the rest of the brain. As time passes—sometimes with the help of a good night’s sleep—memories attach themselves to more robust cortical networks, while the seahorse slowly and carefully lets go of the memories it has been tending. The other camp argues that this is too simple. This group adamantly insists that the seahorse holds on to memories, especially the personal, vivid sort that we remember in something resembling a personal memory theater, at the same time as they are also stored deeper in the cortex. Every time we recall a memory, they say, the hippocampus is involved and “overwrites” the original memory, each time with a slightly new interpretation or reconstruction.

In the same way as the seahorse’s ocean ecosystem is important to understanding its existence, the hippocampus’s brain ecosystem is important to understanding how memory is kept and recalled. In the past few years, people have been paying more attention to how the hippocampus interacts with the rest of the brain. Memories play out in physical networks, where different parts of the brain move as in a synchronized dance. It’s visible with modern MRI methods. William James, one of the fathers of psychology, understood it already in 1890:

“What memory goes with is, on the contrary, a very complex representation, that of the fact to be recalled plus its associates, the whole forming one object, … known in one integral pulse of consciousness … and demanding probably a vastly more intricate brain-process than that on which any simple sensorial image depends.”

In other words, each memory consists of different bits and pieces brought together in one unified wave of consciousness. Each part of the memory originates in a different part of the brain, where it first made a sensory impact. To make the whole thing feel like one experience, one unique memory, requires intricate brain interaction. William James didn’t know exactly how this worked, but thinking of memory and mind the way he did in the 1890s was remarkable. When James was alive, people thought of each memory as a unit, a copy of reality, like something that could be pulled out of a folder in a filing cabinet. That the key to understanding memory was the seahorse—slowly swaying in rhythm with the sensory areas and the emotion and awareness centers of the brain—wouldn’t be discovered for another hundred years. Just a few years before James’s armchair observations, researchers had discovered how neurons are connected to each other with a slight gap in between them called a synapse: the so-called neuron doctrine. From that discovery to today’s brain research, where we can virtually watch memories come to life in the brain, has been a long journey.

We can all benefit from making that journey and learning more about our memories. A small seahorse turned out to be the key to many of the brain’s mysteries. When Julius Caesar Arantius named it the hippocampus, it probably was not solely due to its appearance. Seahorses, like silkworms, were special and somewhat mysterious during the Italian Renaissance. When an event is special and unique, it helps the hippocampus hold on to it as a memory. We know that now, but Arantius could not have known that about the tiny part of the brain he had discovered. He just wanted his discovery to be noticed—and remembered.