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1995 LECTURE SERIESThe Fragile Power of Human MemoryDr. Daniel Schacter
One character in the novel, Jose Juandia, comes up with the idea to mark everything in the village. Jaundia decides to hold off the memory loss by writing labels for everything in the village -- what it is and how it is used. But things turn out to be a little bit more complex: "(Jose) went to the corral and he marked the animals and plants -- cow, goat, pig, hen, banana, and so forth. But little by little studying the infinite possibilities of loss of memory, he realized that the day might come when things would be recognized by their inscriptions, but that no one would remember their use." So then Juandia was more explicit. The sign that he hung on the neck of the cow was an explementary proof of the way in which the inhabitants of Mocando were prepared to fight against loss of memory. He writes out, this is the cow, she must be milked every morning so that she will produce milk and the milk must be boiled in order to be mixed with coffee to make coffee and milk. So what Juandia comes to realize is that if you have a progressive loss of memory, as you move through these different layers of memory, eventually you get to a point where people cannot function, even in the most rudimentary ways. This vignette is revealing because it reminds us of the vast and numerous ways in which memory is essential to just about every aspect of our everyday lives. We think of the manifold ways in which memory influences even the simplest tasks that we perform. We can easily see how a plague that wipes out memory would wreak havoc on human existence. It is a stark illustration of the power of memory. But as powerful as memory is, it is also extraordinarily fragile. Memories are not like compact discs. They are subject to distortion and destruction. They are subject to forgetting and they are subject to destruction by various brain diseases. In memory we witness a paradoxical duality --magnificent power and intricate fragility -- that holds much of its fascination. It is the source of our identity. It is the source of what we do in life. But it is delicate. It can lead us falsely. And, since it is dependent on the brain, it is vulnerable to various kinds of insult and injury. The fragile power of memory is evident in many sectors of our society. Consider the aging population and the problem of Alzheimer's Disease. The progressive loss of memory seen in Alzheimer's Disease is not unlike what Marquez described in his novel. Alzheimer's first strikes our ability to remember personal experiences. The disease progresses through global demensia and, ultimately, destroys our entire memory system and virtually all forms of knowledge. Public attention on this disease has helped to illustrate the great power and critical importance of memory. But the deterioration of the mind as caused by Alzheimer's also reinforces our dependence on memory and our reliance on the integrity of delicate intracranial structures. A more controversial reminder of the fragile power of memory has recently arisen in the courts. The debate centers on the accuracy of memories of long past events recovered in psychotherapy. These memories often involve horrible experiences of sexual and other kinds of abuse that people have apparently forgotten for years. Patients in therapy have come to claim, with tremendous subjective conviction, that these grotesque incidents indeed happened. People accused of having perpetrated the acts many years ago claim with equal passion that nothing happened and that the memories were implanted in therapy. A similar phenomenon has been evident over the past decade in accusations made against child care workers concerning horrible acts of molestation allegedly perpetrated on young children. In some cases, these accusations have been based on the memories of young children -- which can be terribly accurate but also subject to suggestion. Some have argued that these memories are often implanted by law enforcement officials and therapists too eager to infer the existence of abuse where none exists. In all of these scenarios, the power and fragility of memory is displayed. The paradox of memory is also evident at the societal level as a cadre of historical revisionists has sought to question the existence of the Holocaust with claims that much of the horror surrounding World War II simply never happened. Even at this level we see how memories, the most powerful force for determining both what a society believes about its past and how it acts to shape its future, can be fragile enough to whither under attack or suggestion. In considering memory in these broad terms, it is clear that it is a fundamental problem for science. We think of memories encoded in cells and synapsis at the most molecular level. We think of memory operating at the systems level in different parts of the brain. We think of memory as a purely psychological phenomena and ask questions about how accurate it is. We think of memory at a societal or cultural level and ask questions about how societies remember their past. However, for the sake of brevity, we will limit the scope of this discussion to considerations of memory based upon primary research that explores the interface between brain systems and psychological aspects of memory. More specifically, this talk will focus on three main themes. The first is that memory is not one thing. One of the most important insights gained from research in neurobiology and cognitive psychology over the last 10 to 15 years is that memory is not a unitary, monolithic entity. To understand memory, we must distinguish among a variety of forms or kinds of memory. The second theme to consider is the notion of accuracy in memory and memory distortion, and how both relate to brain structure and function. The third and final is the relationship between emotional trauma and memory. In considering the notion that memory is many faceted, it is important to first draw a distinction between explicit memory and implicit memory. Explicit memory is the kind of memory we depend on in everyday life. It refers to our conscious recollections of our past experiences -- remembering what we had for breakfast today, remembering how you got to work today, remembering what the ocean looks like. In studying memory, one of the first problems to confront is how to control memory system input. In the laboratory, we study explicit memory by showing people a series of words, a series of pictures, a video tape -- anything which enables us to control input. The next step is usually a recall test (...tell me about the pictures you just saw) or a recognition test (do you remember seeing this word before, yes or no?). But there is a whole other domain of memory that need not involve explicit recollection at all. It is what I refer to as implicit memory. Implicit memory refers to the unintentional, nonconscious effects of prior experience on subsequent performance. This is the kind of memory of which we are not aware. It is the memory that shows up in improvements in the way that we perform a task, in the ease with which we execute a skill even though we need not remember anything about the particular episodes or occasions in which we acquired the skill or anything about the particular episode that is now influencing our performance. It is a nonconsciousness form of memory. One example of implicit memory is learning to ride a bicycle or other everyday examples that involve learning motor skills. You don't have to remember the previous episodes in which you practiced riding the bicycle, but even if you don't remember those episodes, you can benefit from prior practice. Skill learning, or the learning of procedures involved in performing the task, is another example of implicit memory. One interesting thing is that patients with certain kinds of brain damage can still learn new skills in normal ways. They show this memory implicitly by improving their performance without the ability to remember the past episodes in which they acquired the skills. One particularly fascinating example of implicit memory is a phenomenon known as priming. The priming effect describes the increased recognition or recall by a subject of particular objects or words to which the subject has had previous exposure. For example, a subject is shown the word "octopus" for a split second. Some time later, the subject is asked to complete an incomplete word, "Oct--." Previous exposure to the word "octopus" increases the likelihood that the subject will write "octopus" as opposed to "October" or "Octagon." What is particularly interesting about the priming effect is that it doesn't matter whether the subject remembers having seen "octopus." The subject is still as likely to show priming whether he or she remembers having seen the example or not. Moreover, study has shown that subject's explicit memory for having seen octopus declined over a set amount of time up to one week while the priming effect was steady over the same amount of time. One of the most important insights into priming has been gained through the study of patients with brain damage that produces amnesiac syndromes. These patients exhibit such severely impaired explicit memory that they are unable to remember their past experiences. Amazingly, these patients, despite the severe impairments to their explicit memories, show normal priming effects. One important amnesiac patient case involves a British artist named David Jane. While on a vacation to Brazil in 1989 Jane began to experience horrible headaches. The pain got worse and worse until it finally got so bad that he passed out and was taken to the hospital. Jane's next memory was waking up in England one month later. He had no idea who he was and could not remember anything about his past. What had happened to David Jane is that he had suffered an infection of Herpes Simplex Encephalitis. It's a virus that can cause severe memory loss for reasons that are not terribly well understood. It has a predilection for attacking some of the structures that are important for explicit memory. But fortunately for Jane, the virus primarily attacked these structures on the left side of his brain. Since this is the side which tends to be associated with verbal memory and verbal cognition, Jane could still paint. During the early days and weeks of his convalescence he started doing paintings of the MRI scans, or brain scans, that showed the damage that caused his severe amnesia. Jane's paintings reveal severe damage to his medial temporal lobe. Through Jane and other amnesiac patients, we now know that this part of the brain -- the inner section of the temporal lobe -- is largely responsible for explicit memory. Accordingly, amnesiac patients, for example, would have a terrible time remembering what they had for breakfast this morning. They would have a terrible time in just about any domain of explicit memory. Yet, their intelligence is generally intact. Their ability to engage in conversation and their perception of the world is fine. It's not a global dementia. They simply have this terrible deficit of explicit memory. Another everyday example is an amnesiac patient of mine with whom I occasionally play golf. Now, playing golf requires more forms of memory than you might think. To play the game reasonably well, you have got to have skill or procedural memory of how to swing a golf club. There is also a wealth of jargon involved -- birdie, chip, divot, bogey, etc. -- that requires considerable semantic memory. Moreover, there are all kinds of explicit episodic memory for the events of the round. To keep score, you've got to remember your strokes. If you want to find your ball, you have got to remember where you hit it. When I first took this amnesiac patient out to play a round, the results were quite revealing. He played about as well as he ever had in the past. His procedural memory was fine. He knew all the jargon, all the words, all the strategies. His general semantic memory seemed to be fine, but he just could not remember even the simplest events that occurred during the round. He could never remember his score at the end of each hole (I sometimes minimized mine, but that was motivated amnesia -- a different animal). Most striking, he could hardly ever find his ball off the tee (I could hardly ever find mine, but, again, a different animal). One occurrence, which repeated itself several times the course of the round, is particularly illustratrative of the profound loss of memory associated with amnesiac syndrome. My patient would hit a terrific drive into the fairway. Pleased, he would excitedly begin to consider his next shot. I would then hit my drive and head off the tee and up the fairway. Turning around to find my partner I invariably looked to see him teeing the ball up again. I said, "What are you doing?" He said, "Well, I want to play the hole, too." I said, "Well do you remember just hitting that great drive about a minute ago?" And he looked at me with a look of complete astonishment. He had no idea what I was talking about. He had totally forgotten the drive that he had just hit a minute ago. Obviously, this is real devastation of the medial temporal lobe memory system, those structures in the inner parts of the temporal lobe that are critical for establishing new memories of episodes and experiences that can be remembered consciously and explicitly. Yet patients like this do perfectly fine in priming tasks. This tells us that implicit and explicit memory depend on very different brain structures. Explicit memory depends on the medial temporal lobe. Implicit memory does not. Shifting back to explicit memory, because of the controversy surrounding the reliability and accuracy of memories of childhood abuse recovered in psychotherapy, it's important to consider issues of memory distortion and false memory. This has become an explosive issue in society because of uncertainty about the extent to which these memories are accurate. This is a very complex issue with a number of different questions that must be torn apart and addressed very carefully. Now there's no question that our explicit memories can be highly accurate. Memory, after all, is an adaptation that's evolved over time and it wouldn't make much sense if we had evolved with a distorted memory system. Consider, for a moment, the case of a man who left his home village in Italy in the late 1950s and settled in San Francisco. In the early Î70s he was afflicted by a strange illness. Nobody is quite sure what it was but he emerged from his illness with vivid, hallucinatory memories of the village that he had left some 15 years earlier. And although he was not trained as an artist, he felt compelled to paint these memories. One of the museums in San Francisco was so intrigued that it sent a photographer to this man's village. The photographer took with him reproductions of the man's paintings and set out to capture on film what the man had painted. The results were astonishing. When placed side by side it is nearly impossible in some cases to distinguish between painting and photograph. The detail is that striking. Remarkable examples like this Italian painter and other laboratory research clearly demonstrate that memory can be highly accurate. But we know that memory is also susceptible to distortion and contamination. When leading questions are introduced, people can often incorporate questions into their memories of past events -- even when the questions refer to events that never happened. Not surprisingly, memories seem to be particularly susceptible to suggestive influences as they age and original recall of an episode weakens or degrades over time. But memory can be subject to distortion even under more benign conditions. Psychologists refer to this phenomenon as false memories. False memories most often occur as a result of a source memory problem. For this reason they can be subjectively compelling because the foundation for the memory -- or source -- is somewhat fluid. If your brain confirms a memory as truth then that's what you have. There is no second opinion. There is a lot of evidence now from cognitive psychology experiments to suggests that when we lose access to source information -- information about where an episode took place, who told us something and what they told us -- we become very susceptible to memory distortions because we retain aspects of an event, but we can't remember if that event was real or imagined. Was it something that was said to me? Was it something that actually happened? Once we lose source information we become very vulnerable to memory distortion. As it turns out, investigation has some interesting links between brain damage and false memory and source memory. The frontal lobes are the largest area of the brain and they play a role in many different cognitive and memory abilities. Damage to certain parts of the frontal lobes, particularly on the outer surface of the frontal lobes, results in interesting kinds of memory distortions in patients who are otherwise relatively okay. Frontal lobe damage leads to a high incidence of source amnesia. For example, you can teach a patient a made up fact such as Bob Hope's father was a fireman. In an experiment we then asked patients a little while later, "by the way, do you know what job Bob Hope's father had?" Patients would say, "oh, yeah, he was a fireman. I remember that." We would then ask how they knew Bob Hope's father was a fireman and they would say things like, "I always knew that," "I heard it on television the other day," "I read it in the newspaper," or "everybody knows that." They exhibited source amnesia. They remembered the fact. They thought it was a real memory of theirs, but they couldn't locate the source. It's worth noting that aging is usually accompanied by some frontal lobe deterioration. Accordingly, as we grow older we become more susceptible to source amnesia. The key point to remember, though, is that source memory is tied to frontal lobe structures in the brain. Confabulation is another memory distortion problem that arises as a result of frontal lobe damage. Confabulation refers to the process through which patients will make up stories about events that never happened. Typically, a patient retrieves bits and pieces of the past but puts them together inappropriately. Along the way patients lose the ability to monitor the verticality of the memories and to verify their accuracy. Another important area in the study of memory is its relationship to emotion and trauma. This is particularly important as it relates to recovered and repressed memories. The psychological literature reveals that highly emotional experiences tend to be the best remembered. One of the most compelling phenomena of this kind is known as flash bulb memories. It is this phenomenon that allows so many people to remember exactly where they were when President Kennedy was shot or when the Challenger exploded. With these highly unexpected and vivid events the brain basically takes a picture of the surrounding circumstances and, hence, the term flash bulb memory. But the accuracy of even flash bulb memories can be questionable. Recent studies have shown that, even with these highly vivid memories, people can sometimes be dead wrong about when and where they were when they experienced the memory. The psychologist Alaric Nicer conducted the following experiment. One day after the Challenger explosion he asked a large sample of people where they heard the news. Three years later he asked the same people the same question: where were you when you heard news of the Challenger explosion? Somewhat surprisingly, Nicer recorded some wild deviations in the responses. On balance the evidence suggests that emotionally traumatic memories tend to be better remembered than more ordinary memories. Just the same, there is a lot of evidence to indicate that even these most vivid memories are not immune to decay and distortion. More recently, new studies (conducted at UCI by Larry Kahill and Jim McGaugh and their colleagues) suggest a link between emotional memory and some of the hormones that control and affect brain structures such as the imegula in the medial temporal region. But enhanced memory is not the only consequence of strong emotion. There are conditions under which powerful emotional experiences can lead to poor memory and even amnesia. This is a rare occurrence but it does happen. In some extreme cases people can forget much of their personal past after an emotional trauma. I had a patient in the early Î80s who was found wandering the streets of Toronto with no idea who he was. The story behind this is that the patient had lost his memory as a consequence of the recent death of his grandfather. In this case, the patient's parents had abandoned him as a child and he had been raised by his grandfather. His grandfather had a special role and when he died unexpectedly this young man left the funeral and started wandering aimlessly. When he was picked up, he had no idea who he was or where he'd come from. He couldn't answer any questions about himself. As it often happens in these rare cases, his amnesia cleared up a few days later when he was watching television. The program was "Shogun" and it features an elaborate funeral/cremation sequence that somehow sparked his memory of his grandfather's funeral and the rest of his past. The interesting thing about this patient is that his memory deficit was not global. For example, we gave him a test known as the famous faces test in which the patient is shown the faces of famous people and asked to identify them. He performed well. Indeed, he performed the test at the same level both before and after his amnesia had cleared up. Even when he couldn't remember his name he still had good general semantic knowledge of some past learning. This is another poignant example of the disassociation between different kinds of memory. There is a story of a little Jewish girl who was sent to Bergen Belsen. It is a story that perfectly, painfully illustrates both the power and fragility of memory. When this girl was being loaded onto a cattle car bound for the camps, her mother gave her a poison pill to insert in a tube and to keep with her at all times in the event that things got unbearable. But she threw the pill away. In its place, she inserted into the tube some photos --pictures of herself and of her family. This poor child later described how, as she was brought to the camp, she wanted to remind herself of how she really looked and who her family was. She wanted to remind herself of where she came from. To keep the Nazis from finding her family photos, her memories, she had to hide the tube in her rectum. From time to time, when it was safe, she would remove the tube, take out the pictures and look at them. She was able to remember her past. In her recollections she talks about how she was reminded of her goodness. She was reminded that she was from people, not stone, and that she had a family. She was willing to risk a great deal of discomfort, even torture, in order to carry those memories with her. And more than any science, her courage and desire demonstrates the power and fragility of memory. Memory defines who we are and who we will become. It is fundamental to our understanding of self, both as individuals and societies. But memory is also delicate and must be protected vigilantly, for it can abandon us in the most unexpected and unpredictable ways. It is truly a wonder. |
Irvine Health Foundation |