Speak, Memory, Vladimir Nabokov called his book about his childhood years, and in this incantatory title we can hear our human dread of forgetting. “The cradle rocks above an abyss, and common sense tells us that our existence is but a brief crack of light between two eternities of darkness,” reads the book’s first sentence. The crack of light may be described as memory itself—that fickle and unreplicable network of experience and associations from which we construct who we are, who others are, and what we may expect from them and from ourselves.
In the broadest sense, memory is consciousness, because what the brain is doing at all times and in all of its operations is remembering. More often than not, it is a matter of practical cognition: knowing where we left the keys, and then, once we have located them, what the keys are for. But within such memories are vestiges of our emotional and sensorial lives, an intimate network of recollections, unique to each of us, that keys conjure. The neurosystem in which this cascade of memory occurs, with its branches and transmitters and ingeniously spanned gaps, has an improvised quality that seems to mirror the unpredictability of thought itself. It is an ephemeral place that changes as our experience changes, to the point where we are incapable of remembering the same event in exactly the same way twice.
In her fascinating book about memory loss and the efforts of scientists to understand it, Sue Halpern reports an experiment in which members of the Cambridge Psychological Society were asked to reconstruct a meeting of the society that had taken place two weeks before. The average person was barely able to recall 8 percent of what had happened, and almost half of this was incorrect, peppered with the recollection of events that had never occurred or that had occurred elsewhere.
Such paltry power of retrieval in an educated, and supposedly attentive, group is not surprising. Memory, Halpern reminds us, “is not an archive,” nor does it record in real time. It lives in the brain “in chemical traces. The traces can fade…and they can be augmented,” depending on one’s experience and observation. The intensity of an experience may sharpen the memory of it, while making it even less accurate. During situations of extreme stress, for example, the body is flooded with damaging amounts of the hormone cortisol, causing communication relayed by neurotransmitters and other chemicals in the brain to break down. Halpern recounts the case of an Australian forensics expert named Donald Thomson who was a guest on a television show devoted to exploring the unreliability of eyewitness testimony:
Not long afterward [Thomson] was summoned to a police precinct, put in a lineup, and identified by a woman as the man who had raped her. Though he had an incontrovertible alibi—he was on national television at the time of the attack and seen by hundreds of thousands of viewers—he was charged with the crime on the basis of her unwavering eyewitness testimony. It was only later, when an investigator discovered that the woman’s television had been on during the assault, that it became clear that in the midst of her trauma, the woman had conflated Thomson’s face with that of the rapist.
In spite its unreliability, however, our memory is the fullest record we have of ourselves. We live through it as we live through breathing, and not only in the figurative sense: in the most advanced stage of Alzheimer’s—a disease that first strikes the hippocampus, where short-term memory is created, before spreading throughout the rest of the brain—one forgets, on a muscular level, how to exhale.
Halpern’s central aim in Can’t Remember What I Forgot is to find out how memory loss occurs, when it ceases to be a normal condition of aging and becomes a disease, and what the prospects are for the development of a drug that can stave it off. Playfully, she frames her investigation as a quest for esoteric knowledge: skeptical, open-minded, and omnivorously curious, she goes where the rest of us cannot go, penetrating the inner sanctums of America’s memory research labs to bring back the news. She twice submits herself to injections of radioactive material in order to get up-to-the-minute functional images of her brain; undergoes hours of paper-and-pencil neuropsych exams that put her memory and spatial reasoning to the test; takes a cognitive stress test (in which the brain takes in new information, encodes it, and retrieves it, while the MRI takes “pictures that show which parts of the brain are being activated, which parts are working harder than normal”); attends memory-boosting seminars; and at home practices a variety of mental exercises designed to sharpen her cognitive prowess.
In San Francisco, Halpern sits in on a “brain-fitness class.” And in Manhattan she witnesses a one-on-one session at a psychologist’s office, where
a fellow in his forties who wanted to “stay sharp” was coached through a series of mental stretching exercises adapted from a rehabilitation regimen originally designed for stroke victims and people with traumatic brain injuries. There was nothing particularly wrong with him, he said, but he was now single, after years of marriage, and he was hopeful that a tuned-up memory would give him an edge in the dating game.
At one point, at UCLA’s Brain Mapping Center, Halpern has her hippocampus “unfolded,” using magnetic resonance imaging and math, in order to measure the thickness of each of its six cortical layers. The thicker each layer is, the healthier, since Alzheimer’s begins with a thinning of the hippocampus’s entorhinal cortex—an important memory center in the brain—as a result of the death of neurons there. (In non-Alzheimer’s memory loss a different node of the hippocampus is affected, the dentate gyrus.) When neurons in the entorhinal cortex fail to project into the next region of the brain, the neurons in that region die as well, starved of the connections needed to keep them alive. Recent recordings taken from the brains of epilepsy patients show that specific spontaneous memories are stored in specific neurons in the hippocampus.1 As those neurons fail to ignite, the capacity for free recall diminishes until it is wiped out entirely. The loss is sequential. “This may be a fifty-year process,” Dr. Susan Bookheimer of the Brain Mapping Center tells Halpern. “It’s a long process that will spread and spread.”
In all of the tests, Halpern’s brain performs well, but this fails to assuage her anxiety about the future. She knows that early detection of Alzheimer’s is difficult, and that, as with many types of cancer, by the time impairment is diagnosable it’s too late. Moreover, early detection comes with psychological peril, since there is no treatment capable of warding off dementia’s later stages. Most people reasonably prefer ignorance to certainty when given the choice of knowing whether they will get a disease with no cure. Halpern writes that when signs of Alzheimer’s show,
this is when you begin to say that someone is not herself. We even say this about ourselves. But how can that be?… How can you be anything but yourself? The obvious, rational answer [is] that you can’t…. You are only yourself now. And what if that self is one who can’t remember itself? What if the person you had been is only a memory…held by others?
These questions go to the heart of our anxiety about memory loss. According to a survey conducted by the MetLife Foundation, in 2006, Americans over the age of fifty-five fear getting Alzheimer’s more than any disease. (Among respondents of all ages, Alzheimer’s was second only to cancer.) Near the beginning of Can’t Remember What I Forgot, Halpern gives a brief description of her father’s mild cognitive impairment (MCI). He is in his mid-seventies, and he knows how disorienting it is “to pick up the phone to call a friend, whose funeral he’d attended two years earlier.”
During the year before his death he would often sit at “the kitchen table from breakfast till lunch staring at a single page of the New York Times.” Halpern’s mother has bought him a key-chain recorder with his name and address in case he gets lost, but he dies before having to use it. The doctor has assured Halpern that he did not have Alzheimer’s, but he never underwent an autopsy that would have shown unequivocally whether the gummy mess of beta-amyloid plaques that is the telltale symptom of Alzheimer’s had infected his brain.
Not everyone with MCI goes on to develop Alzheimer’s, and some people diagnosed with MCI turn out not to be impaired. Comparing people with MCI at the time of diagnosis and two years later, Susan De Santi, a psychologist at NYU’s Center for Brain Health, found that some actually went back to being normal. For the most part, these people were younger and more educated than the group as a whole, suggesting that, through various means of intellectual and physical stimulation, they had developed alternative neural pathways that allowed them to make up for weaknesses in other parts of their brains. It was a kind of cognitive reserve. De Santi tells Halpern in a “quiet and conspiratorial” voice:
People think that MCI is only about memory, and in fact, only those who converted to AD had significant declines in memory. But we also found that it’s not memory alone. It’s memory problems combined with problems in some other cognitive domain, like fluency or spatial reasoning. Seventy-one percent of those who had memory problems and some other problem ended up getting sick with AD, but only eight percent of people who only had memory problems got sick…. For people who went back to normal, the significant thing was that they had no attention deficits. Attention, not memory, was really the key.
But of what comfort is all of this diagnostic wisdom in the face of a disease that strikes, with alarming frequency, a growing population of elderly people whether they are educated or not?2 John Bayley, in Elegy for Iris, his memoir of his marriage to the novelist Iris Murdoch, who suffered from Alzheimer’s during the last years of her life, likens her mental state to that of one condemned to collect water with a sieve. Language is one of the first faculties to break down. Their mode of communication, Bayley writes, “seems like underwater sonar, each bouncing pulsations off the other, then listening for an echo.” Even when words come, they are not accompanied by “that wordless communication which depends on the ability to use words.”
A particularly diabolical feature of Alzheimer’s is that, while all else has washed away, “emotional memory” is retained, so that the patient finds himself in a prison of feeling without context. A friend has told me of his normally mild-mannered father who, enraged at being unable to figure out how to insert his key into his locked car, hacked the door off with an axe that he kept for splitting firewood. He began eating soap, toilet paper, and worse—extreme behavior, but not untypical. To tamp down his delusions, he was given haloperidol, an antipsychotic medication that blocks the manufacturing of dopamine in the brain, thereby accelerating his cognitive decline.
Hagar Gelbard-Sagiv, Roy Mukamel, Michal Harel, Rafael Malach, Itzhak Fried, "Internally Generated Reactivation of Single Neurons in Human Hippocampus During Free Recall," Science, October 3, 2008, pp. 96–101.↩
According to a National Institute of Mental Health study cited by Halpern, starting at age sixty-five the average American's chance of developing Alzheimer's disease is 10 percent. About half the people who reach age eighty-five experience "diagnosable symptoms." In public discussions about Alzheimer's it is often said that 5 percent of Americans already have the disease, though some may still be asymptomatic. If true, this is almost twice as many as suffer from manic-depressive psychosis and schizophrenia combined.↩
Hagar Gelbard-Sagiv, Roy Mukamel, Michal Harel, Rafael Malach, Itzhak Fried, “Internally Generated Reactivation of Single Neurons in Human Hippocampus During Free Recall,” Science, October 3, 2008, pp. 96–101.↩
According to a National Institute of Mental Health study cited by Halpern, starting at age sixty-five the average American’s chance of developing Alzheimer’s disease is 10 percent. About half the people who reach age eighty-five experience “diagnosable symptoms.” In public discussions about Alzheimer’s it is often said that 5 percent of Americans already have the disease, though some may still be asymptomatic. If true, this is almost twice as many as suffer from manic-depressive psychosis and schizophrenia combined.↩