| The Memory Issue | Autumn 2008 |
What Tangled Webs People with Alzheimer’s disease not only fail to remember previously learned information, but they also experience distortions of memory and false memories. Distortions of memory may include simple but critical aspects of daily life. Alzheimer’s patients may falsely remember, for example, that they have already turned off the stove or taken their medications, leading them to neglect these tasks. More dramatic distortions of memory occur when Alzheimer’s patients substitute one person in a memory for another, combine two memories, or believe that a long-ago event occurred recently. These distortions may fall under the definition of confabulation—when people fill a gap in their memory with a fabrication they believe to be true. Sometimes a false memory can be confused with a psychotic delusion or hallucination. A person may claim, for instance, to have recently seen and spoken with a long-deceased family member. Although visual hallucinations are part of Parkinson’s disease dementia and dementia with Lewy bodies (dementias that are characterized by parkinsonism, visual hallucinations, and fluctuations), an Alzheimer’s patient is usually more likely to suffer from a memory distortion or a false memory than a true auditory and visual hallucination. The same is true for patients who claim that someone has broken into their house and rearranged their belongings. That these symptoms likely represent false memories rather than true hallucinations or delusions has treatment implications, as false memories respond better to memory-improving medications than to antipsychotics. My interest in memory distortions began with a simple clinical observation: most of my patients with memory problems triggered by mild Alzheimer’s disease could not live alone, while most of my patients with memory problems stemming from encephalitis, temporal lobe epilepsy surgery, and other etiologies could live independently. It was clear that something other than simple memory loss was at work in those with Alzheimer’s. My discussions with patients and their caregivers soon showed that false memories and memory distortions made the use of routines and reminders more difficult for Alzheimer’s patients than for those with memory loss from other conditions. Bearing False Witness At Bedford Veterans Administration Hospital in Massachusetts, my colleagues and I began our research into memory distortions by creating false and distorted memories in healthy older adults and then determining whether Alzheimer’s patients could use the same mechanisms that the healthy participants used to suppress these false memories. We created false memories by presenting healthy people with a list of words—such as candy, sour, sugar, bitter, taste, honey, heart, and cake—that related to a theme word, which was not itself presented. Study participants were highly likely to falsely remember on free-recall tests and falsely recognize on recognition memory tests the theme word—in this case, sweet. (Even healthy younger and older adults falsely recognize more than two-thirds of such theme words.) One way to reduce false recognition in healthy individuals was simply to have them repeat the theme word several times. These repetitions helped them recall particular words, thus allowing them to resist the lure of the non-presented yet central theme word. In two studies, we found that repetition allowed healthy older adults to develop specific recollection of words on the list, which in turn reduced their rate of false recognition. Among Alzheimer’s patients, however, repetition only helped them grasp the theme of the list, thus leading them to err more often in choosing the theme word, paradoxically increasing their false recognition rate. Another way that healthy individuals reduced false recognition of related words was by pairing the words with pictures. Although this reduction could simply reflect the fact that pictures are better remembered than words, researchers at Harvard University have shown that false recognition decreases because the stories that form from picture–word pairings are more distinctive, and thus, more memorable. The basic idea of this heuristic is that some events are so distinctive they would have to be memorable. If you were asked, “Have you killed a fly in your office within the past year?” you might find the answer elusive, because for most people killing a fly is neither remarkable nor distinctive. If instead the question was “Have you killed a snake in your office within the past year?” you would answer confidently, because the memory would have been distinct. We investigated whether Alzheimer’s patients could use this distinctiveness heuristic to reduce their false recognition rates. We experimentally determined that Alzheimer’s patients could use the heuristic. Their poor memory, though, limited their ability to reduce their false recognition rate. In Living Memory Studying the frequency of memory distortions and false memories in the real world can be difficult. The terrorist attacks of September 11, 2001, though, provided us an opportunity. We contacted Alzheimer’s patients and healthy older adults with a phone questionnaire within weeks of the attacks, again three to four months later, and finally one year afterward to evaluate both their memory of and emotions about that day. Memory distortions were common among all participants, reminding us that a vivid memory isn’t necessarily an accurate memory. Even healthy older adults showed a high rate of memory distortions—on average 25 percent—as they misremembered such details as where they were and whom they were with when they first heard of the attacks. Alzheimer’s patients showed even less accuracy, with memory-distortion rates approaching 50 percent. In contrast, memory-failure rates—with study participants saying, “I don’t know” or the equivalent—were relatively low: 13 percent in the Alzheimer’s patient group and only 1 percent in the healthy older adult group. Thus, when it comes to remembering personal information related to national traumatizing events, Alzheimer’s patients and healthy older adults are more likely to misremember than to say “I don’t know.” We recently conducted several laboratory studies that also have real-world significance. In one of these studies, we first presented Alzheimer’s patients and older adult controls with sentences that could be either true or false, followed by a label of true or false. For example, “In New York City, the 53rd Street bus will take you uptown: false,” or “It takes 32 coffee beans to make a cup of espresso: true.” Interestingly, although the Alzheimer’s patients correctly remembered that 69 percent of the true statements were true, the same patients incorrectly remembered that 59 percent of the false statements were true. This finding suggests that if you tell someone with mild Alzheimer’s disease that something is false, they are more likely to remember that it’s true. The statement, “The 53rd Street bus won’t take you to your sister’s house, so take the 67th Street bus instead,” for example, will lead an Alzheimer’s patient to be more likely to falsely remember that the 53rd Street bus is the correct bus than if the 53rd Street bus had not been mentioned at all. This finding has significant relevance for clinicians and caregivers who need to communicate with Alzheimer’s patients. Brain Storming To begin to unravel the underlying pathophysiology of these memory distortions in Alzheimer’s patients, we elected to test the role that frontal-lobe pathology may play in the disease. We began by examining false recognition in patients with frontal-lobe lesions caused by stroke or tumor resection. We gave these patients and matched control subjects the same related-word lists we had given Alzheimer’s patients and found that patients with frontal lesions showed even higher levels of false recognition than the Alzheimer’s patients did. Some of our newer research investigates how the brain forms and retrieves memories. In this work, we use 128 channels of EEG to produce a particular type of neural activity as subjects are shown a picture or presented with a previously studied word. We found that when we average the EEG across 30 or so trials, we can see—in real time—the electrical activity associated with retrieving a memory. These studies have shown that, compared with healthy older adults, people with mild Alzheimer’s disease exhibit vastly reduced frontal-lobe activity, thus providing support to the hypothesis that frontal-lobe dysfunction may cause the high levels of memory distortions in people with mild Alzheimer’s disease. An improved understanding of the causes of false memories and memory distortions may lead to behavioral and pharmacological treatments that can decrease their effects. Reducing the effects of these tangled memories may in turn allow patients with Alzheimer’s disease to live fuller, more independent lives. Andrew E. Budson ’92 is director of the Center for Translational Cognitive Neuroscience and the Geriatric Research Education Clinical Center at Bedford Veterans Administration Hospital in Bedford, Massachusetts. He is also director of cognitive neuroscience research at the Alzheimer’s Disease Center at Boston University School of Medicine and a consultant neurologist in the Division of Cognitive and Behavioral Neurology at Brigham and Women’s Hospital in Boston, Massachusetts. Photo: ©iStockPhoto.com |
cognitive testing, she explained more fully: “That’s the problem—he remembers doing things he hasn’t done. When the electric company shut off his power, we found he hadn’t paid any bills for about six months. He swears he paid them all. I worry whether he can keep living alone. He tells me he takes all his medications, but how do I know that’s true?”
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