Probing the Many Riddles of Memory

When the ghost of King Hamlet commands his son to “remember me,” the prince takes the message to heart, vowing to “wipe away” all that is trivial in his accumulated memory, so that “thy commandment alone shall live / Within the book and volume of my brain.” Of course, it’s not quite that simple, and we often find ourselves doing battle with our memories — struggling to recall something that we’ve forgotten, or wishing to forget something that nonetheless intrudes into consciousness.

BOOK REVIEW — “Adventures in Memory: The Science and Secrets of Remembering and Forgetting” by Hilde Østby and Ylva Østby (Greystone Books, 312 pages).

A long-forgotten memory can surface at any time. In Marcel Proust’s “In Search of Lost Time,” the narrator bites into a French pastry known as a madeleine and is instantly transported back in time. Suddenly a childhood memory “revealed itself” — it was the recollection of the snack his aunt used to share with him in her bedroom on Sunday mornings before mass.

Poets and novelists got a head start, but for some 140 years now scientists, too, have been wrestling with memory. It’s this struggle that two Norwegian sisters, the novelist Hilde Østby and the neuropsychologist Ylva Østby, tackle in their engrossing book, “Adventures in Memory: The Science and Secrets of Remembering and Forgetting.”

There has been progress, of course, but as the authors point out, there is much that remains shrouded in mystery. How reliable are the memories associated with traumatic experiences? Can we train our brains to remember better? And what exactly is memory, and how and why did it evolve?

One thing that scientists learned in the last century is that there is more than one kind of memory. Semantic memory is the memory of how the world is, apart from our experiences of it. We exercise our semantic memories when we recall that Paris is the capital of France, for example, or that cats have four legs and spiders have eight. And then there’s episodic memory — our memory of things that have happened to us. It is the loss of episodic memory that makes dementia and Alzheimer’s disease so terrifying. No one wants to be stricken with heart disease or cancer, but diseases of the mind and brain command a special kind of terror. They seem to eat away at one’s sense of self: Without our episodic memories — the record of the unique events that have made each one of us into who we are — what is left?

The world’s most famous memory disorder patient was Henry Molaison, known while he was alive as H.M. He underwent brain surgery to treat his epilepsy while in his 20s, and though he lived into his 80s, he was unable to form new memories — either semantic or episodic — after the operation. He couldn’t name the president of the United States without prompting; he couldn’t remember Suzanne Corkin, the researcher who visited him numerous times (he suspected she might have been a friend from school); he couldn’t even recognize his own aged reflection in the mirror. He could talk about his life before the operation, but only in a fragmentary way, as though he knew only a list of facts but hadn’t actually “been there” as his life unfolded. “He possessed a rather dry encyclopedia about himself,” as the authors put it. As far as we know, “he could not recall lifelike, smelly, noisy, emotional memories.”

Most of us do have these smelly, noisy memories. And, the authors argue, such memories are a uniquely human affair. “No gazelles cringe because they’re thinking about an embarrassing moment two years ago, no leopards experience a flash of happiness when a memory hits them of how they killed their first prey,” the authors write. Maybe not — though certain animals definitely remember, and have some ability to plan ahead (experiments with scrub jays, for example, suggest that they can anticipate their food needs for the next day). At any rate, we humans are certainly masters of leaping through time; like Proust’s narrator, we do it in our heads, and we do it all the time. We vividly imagine the past, and we make plans — often richly detailed plans — for tomorrow.

And here we get a glimpse of why memory evolved in the first place. The better we remember past events, the more successfully we can prepare to exploit the opportunities and avoid the dangers that lie ahead. Indeed, we master these in unison: From about the age of 4, children can relate episodes from their past in vivid detail, as well as plan for the things they want to do the next day. But that doesn’t mean that these two kinds of mental imagining — of the past and of the future — carry equal weight.

From the point of evolution, it is the latter skill that pays off. The psychologist Thomas Suddendorf, one of many experts who the Østbys interview, argues that our ability to vividly remember the past is a byproduct of imagining the future. “Our malleable, unpredictable, yet vivid memory would not have evolved had it not been for its usefulness in creating vivid, insightful scenes of the future,” the authors write. Think of our Stone-Age ancestors: They were not especially fast or strong, but they could envision where a herd of antelope might next be found, and could make axes and other tools today, for use tomorrow — an enormous advantage.

These mental capacities evolved together, and somehow function together — which means that when memory is impaired, our ability to plan for the future is also jeopardized. H.M., who couldn’t form new memories, also had only a vague conception of his own future.

Even when our brains are working normally, we can misremember. In fact, decades of research have shown us just how fallible memories can be, and one of the book’s most compelling chapters focuses on the problem of flawed and false memories.

For starters, we now know how easily memories can be implanted. In one study, Canadian researchers were able to convince 70 percent of their subjects that they had committed a serious crime — either burglary or assault — when they were young. And the work of Elizabeth Loftus, a leading authority on false memories, has highlighted just how unreliable our memories can be. In one investigation, she asked people to relate in detail a particular event that they had witnessed. Then they were given written accounts of the event in which some small detail — the color of a sweater, for example — had been changed. Many participants didn’t spot the change, and went on to trust the written account over what they had actually seen.

The implications can hardly be exaggerated: What might begin as a courtroom stenographer’s mistake could lead to the wrong person being convicted. One result is that the criminal justice system has been forced to re-think the value of eyewitness testimony. Back in the 1970s, the authors write, the courts imagined “that memory functioned as a precise documentary: expose the film, and you’ll have a murderer.” We now understand that it’s not so simple. In many cases where a defendant was convicted but later exonerated due to DNA evidence, the initial conviction turns out to have been based on eyewitness testimony. The witnesses had no ill intent; they simply misremembered.

All we can do is to strive to be aware of these shortcomings. (One of the book’s few clunky episodes is a scene in which the authors attempt to implant a false childhood memory in the head of their Norwegian editor, a man named Erik, with the help of some doctored photos. But Erik is overly suspicious — these women are writing a book with a chapter on false memories, after all — and doesn’t take the bait.)

If remembering is a continuous struggle, forgetting might seem like something to be welcomed. At least, if it were a choice. But as we age, the forgetting is often thrust upon us. The authors, however, are sanguine about this, seeing it as a tolerable compromise. “The truth about forgetting is that we are forced to live with it, embrace it, and let it do the job of chiseling out the most important things that will stand out like monuments in our memories,” they write, “even if that means forgetting all those little things we wish we could remember.”

Prince Hamlet couldn’t have said it better.

Dan Falk (@danfalk) is a science journalist based in Toronto. His books include “The Science of Shakespeare” and “In Search of Time.”