Forgetting: The Benefits of Not Remembering

PROLOGUE

Funes not only remembered every leaf on every tree of every wood, but even every one of the times he had perceived or imagined it.

I suspect, nevertheless, that he was not very capable of thought. To think is to forget a difference, to generalize, to abstract.

—

Jorge Luis Borges

, Funes, the Memorious

As a memory specialist, all I hear about is forgetting. And not just from my patients, who typically have disorders that cause pathological forgetting and are expressing a valid medical concern. I mean from nearly everyone else, the vast majority of whom are complaining about normal forgetting, the forgetting that we are born with and that naturally varies among us like height or other traits. I am not complaining about these complaints. My own forgetting is frustrating, and besides, offering compassionate advice is a privilege of doctoring. I am quite sure, in fact, that my early interest in memory—triggering my academic interests, training, and career—was influenced by my own forgetting. Who wouldn’t want to have a better memory? To perform better on exams; to remember with high fidelity books read or movies watched; to have more details at the tip of one’s tongue to win over minds in intellectual debates or hearts with fun facts and poetry?

That forgetting represents a glitch in our memory systems, or a nuisance at the very least, has always been the common scientific view. Accordingly, science has primarily focused on figuring out how the brain forms, stores, and retrieves memories; how the memory snapshot is taken, processed, and cataloged. While some scientists have intuited forgetting’s possible benefits, the fading of memories, like musty photos in an attic, is usually considered a malfunction of the recording device or a sign of the flimsiness of the record. This standard view, in which better memory is always the noble goal, whereas forgetting is to be prevented and fought tooth and nail, has guided my training and my career.

I have been a student of memory for more than thirty-five years. As an undergraduate in experimental psychology at NYU, I wrote my first published paper and graduating thesis on the topic of how our emotions can bias what we see and how we remember. As an M.D./Ph.D. student at Columbia University, I worked in the lab of the memory researcher Eric Kandel, who in 2000 was awarded the Nobel Prize in Physiology or Medicine for his discoveries regarding how neurons in different animal models remember. And since completing a postdoctoral fellowship at Columbia on Alzheimer’s disease and other forms of memory failure with Richard Mayeux, a leading Alzheimer’s clinician and geneticist, I have been toiling away in my own lab investigating the causes of, and potentially the cures for, Alzheimer’s disease and other reasons for memory failure in later life.

While old dogs can’t learn new tricks, it’s a good thing we can forget old ones, since it turns out that I, along with many other memory investigators and memory doctors, was wrong about forgetting. Recent research in neurobiology, psychology, medicine, and computer science has contributed to a clear shift in our understanding. We now know that forgetting is not just normal but beneficial to our cognitive and creative abilities, to our emotional well-being, and even to societal health.

This book is dedicated to the hundreds of patients I have tried to help throughout my career who have suffered from pathological forgetting, commonly caused by neurodegenerative disorders but also simply by aging itself. While the medical definition of pathological is often up for grabs, the easiest distinction between normal and pathological forgetting is that the latter reflects a true worsening of one’s memory, a worsening that impacts the ability to fully engage in our information-laden lives. Only by observing the painful consequences of pathological forgetting in patients does normal forgetting emerge in sharp relief. Witnessing the suffering caused by Alzheimer’s disease inoculates against the temptation to poeticize it—to say, for example, that the pathology carries a silver lining, that it is somehow good. Perhaps. But as a doctor who tries to sympathize as much as possible and is exposed to the suffering caused by pathological forgetting, I cannot abide that position. In any case, this book is not about that. It is about normal forgetting.

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The question presented earlier—Who wouldn’t want to have a better memory?—was obviously posed rhetorically. What about photographic memory, a memory system that immortalizes like a computer hard drive, where snapshots never fade in a mind that never forgets? Most of us have fantasized about this cognitive power, but I suspect many have also sensed its potential burdens. Despite occasional claims in the annals of neurology, cases of true photographic, sometimes called eidetic, memory turn out to be vanishingly rare. There are some people whose natural memory is at the superior end of the normal distribution, like extremely tall variations in height. There are experts in certain fields who depend on particular memory skills so extraordinary as to seem out of this world: memory specifically for chessboard arrangements by grand masters, sheet music by concert pianists, limb movements by professional tennis players. There are also so-called mnemonists, or memory magicians, who rely on cognitive tricks of the trade, some innate skills, and lots of practice to develop superior memories for specific information categories—autobiographical information, numbers, names, or events. When formally tested, however, none of them, it turns out, have true photographic memories for all things. None have minds that never forget.

So photographic memory is really a fabrication, a superhero power. Is it desirable? Until science caught up with fiction to show why not, fictional descriptions provided the early answers. The best example is Jorge Luis Borges’s short story Funes, the Memorious, found in his anthology Ficciones. After being thrown from a horse and knocked unconscious, Funes awakes with an inflamed brain that can no longer forget. Now, in a flash, he can memorize and recollect anything and everything. Envy is what most readers experience when starting the story, as we learn that Funes, endowed with his new super cognitive powers, can effortlessly recite long passages from books recently read or master new languages (even Latin!) in a matter of days. But jealousy transitions to compassion as we begin to appreciate his psychic chaos. In one instance, when Funes is offered a glass of wine produced in a neighbor’s vineyard, his mind drowns in a deluge of memories. The wine revivifies so many associated memories, each with pointillist details—for example, the shoots, clusters, and grapes of the vine from which the wine was pressed—that this total recall seizes Funes with anxiety. No wistful and meandering remembrance of things past for poor, suffering Funes. When asked about any previous event, even a lovely childhood afternoon, his mind is overloaded with the day’s minutiae—the formation of every cloud seen, the minute-by-minute fluctuations in temperature felt, the choreography of every movement of his limbs. Very quickly we realize that total recall can be a nightmare.

What’s most remarkable about Funes, the Memorious is how astutely it foreshadows neuroscientific research into the way a mind that snaps and stores photographs with retina display resolution can impair our thinking. Many of the story’s passages about Funes describe a dominant cognitive impairment caused by his photographic memory: the inability to generalize—to see the forest for the trees. "His own face in the mirror, his own hands, surprised him on every occasion….It was not only difficult for him to understand that the generic term dog embraced so many unlike specimens of differing sizes and different forms; he was disturbed by the fact that a dog at three-fourteen (seen in profile) should have the same name as the dog at three-fifteen (seen from the front)." Having a photographic memory was so distressing that young Funes wound up spending the rest of his life sequestered in a deliberately darkened and pitch-quiet room.

Only in the past decade or so has a new science begun to coalesce to explain why forgetting in balance with memory is the true and very natural cognitive power bestowed on us to live in an ever-fluctuating world, one that is also often frightening and painful. The right to be forgotten was legally determined in European courts in 2010, when it was successfully argued that a permanent record, in this case on the internet, could have damaging consequences for a person’s life. In a similar spirit, our brains are right to forget.

As you shall see in this book, forgetting in balance with memory is required for sculpting cognition: for granting us the flexibility to accommodate to an ever-changing environment, for extracting abstract concepts from a scattered mess of stored information, for seeing the forest for the trees. Forgetting is required for emotional well-being: for letting go of resentments, neurotic fears, and hurtful experiences that fester. Too much memory or too little forgetting imprisons with pain. Forgetting is required for societal health and for creativity, lightening the mind for those eureka moments when unexpected associations are made. Without forgetting, all flights of creative fancy would be moored by memory.

If the rhetorical question posed at the beginning was changed to, Who would want to have a photographic memory with a mind that never forgets? I hope that after reading this book, you will appreciate that the answer is nobody.

ONE

TO REMEMBER, TO FORGET

My mind was like a steel trap! declared Karl, my first patient of the day at Columbia University’s Memory Disorders Center. Among the many metaphors for memory, a steel trap is one of my least favorites—partly on aesthetic grounds (the violent visual of a trapped paw is repugnant), but mainly for its misleading scientific implications. Even for those in the superior range, memory is never steely; it is flexible, form-shifting, and fragmented. The trap metaphor is also mechanically incorrect by implying that memories are formed instantly, with a decisive snap.

A Manhattan criminal defense lawyer, Karl appeared dressed for court. Renowned for its expertise in Alzheimer’s disease and related disorders, our center provides care to a diversity of patients from around the world. Still, Karl stood out, and not just because of the tailored fit of his three-piece suit. When I arrived punctually to the office from my research laboratory a block away, Karl was pacing and raring to go, revealing a hyperkinetic eagerness atypical of our patients. It turned out that he had studied English literature as an undergraduate at Yale, and once he’d dispensed some initial glib proclamations about his superior cognitive abilities and courtroom prowess, he relaxed and began articulating his symptoms and his fears about their causes and their consequences on his active legal career.

Listening carefully to a patient’s symptoms and clinical history is the first order of a neurologist’s business. These testimonials contain rich information we need to achieve our central goal, localizing the lesion. Even more than other medical specialists, neurologists are typically obsessed with asking where? before asking what? The cause of arm weakness, for example, can localize to muscles or nerves, or different parts of the spinal cord, or the brain, and each part of this nervous system map is targeted by different diseases. Most of us admit to taking joy in solving this anatomical puzzle. It requires knowledge of the nervous system’s circuitry, an understanding of how different nodes of the circuit function, and, accordingly, how to probe the circuit in isolating the source of the problem. The joys of our profession aside, localizing the lesion—answering the question of where—is critical for getting the diagnosis right.

Isolating the anatomical source of someone’s malfunctioning memory is harder than isolating the source of a malfunctioning arm, but the same principle applies. Memory specialists begin localizing the lesion that is causing pathological forgetting the second a patient walks through the door. Even during the informal introductory phase, we try to map the function of a patient’s cognitive brain regions in order to get a sense of how their memory network functioned in their premorbid state—that is, before the onset of cognitive symptoms. (Beware, an occupational hazard: we reflexively perform these functional biopsies even when chitchatting in social settings. Just listening to how someone tells a story—that is, how embroidered the details, how rich the vocabulary and syntax—we can’t help but start color-coding the storyteller’s cognitive brain regions according to level of function.) These admittedly blurry cognitive brain maps are a helpful starting point from which we can chart the anatomical source of a patient’s chief cognitive complaints. By the end of the first visit, we try to formulate an opinion on the where of memory loss. Subsequent clinical tests—which may include blood work, neuroimaging studies like MRI, and a neuropsychological evaluation—ultimately confirm or help us adjust that opinion.

Karl had always excelled in school, and even among his academically competitive peers his memory was exceptional, as evidenced by his ability to memorize baseball stats as a boy growing up on Long Island, poems as an undergraduate, and legal torts as a student at NYU’s law school. His outstanding memory was professionally useful and well known throughout his law firm. After meeting someone once—a summer intern, a legal assistant, or, of course, a client—he would never forget that person’s face or name. And this turned out to be his chief clinical complaint: a slippage in recalling clients’ names. Recently, a few months after meeting an important new client, he’d run into her on a bustling Manhattan street and, shockingly, fumbled for her name. Simply an embarrassing nuisance for most of us, stumbling over a name felt to Karl like a serious drag on his career.

—

Just hearing Karl’s history, and listening carefully to his chief clinical complaint, I began formulating a pretty good idea about which parts of his brain might be the source of his pathological forgetting. In fact, I had a strong hunch that it was likely localized to one of two areas, a hunch that I would then try to confirm with a neurological exam and a rudimentary memory test that I perform in my office, then with additional tests that would be administered at the visit’s end. But in order to explain my hunch—and before we can begin to explain how forgetting works—I think an overview of memory will be helpful as I take you through my clinical thinking and evaluation, and on to Karl’s ultimate diagnosis.

Among the many metaphors for memory, a personal computer is a good one. In fact, better than a metaphor, how a personal computer works turns out to be an excellent analogy for how our brains store, save, and retrieve memories. That’s no coincidence, since both computer and brain engineers have to solve the same three problems in learning how best to handle vast amounts of information: where to store memories, how to save memories in the dedicated storage site, and how to open and retrieve memories on demand. For this play of memory, our brains have three main anatomical actors. A collection of regions toward the back of the brain, which for simplicity I will call the posterior area, is where many of our most cherished memories are stored. A structure buried deep in the brain’s temporal cortex, the hippocampus, allows the brain to properly save these memories. And an area in the prefrontal cortex, located right behind our foreheads, is the general area that helps us open and retrieve memories. Whenever you save a document onto your computer hard drive or open a previously stored file, you are playing with your computer’s memory just as your brain does with your own.

Brain areas of memory and forgetting.