Forgetting: What's normal?
| May 1, 2008
In-Depth Report
Forgetting: What's normal?
It's normal to forget some things, and it's normal to become somewhat more forgetful as you age, but it's not normal to forget too much. The question is, how much is too much? Regardless of age, some people's memories are better than others — just as some people are better at math or athletics. How can you tell whether your memory lapses are within the scope of normal aging or are a symptom of something more serious?
Neuroscientists and physicians have not fully answered that question, but they have identified some key differences between normal memory lapses and those that occur with more serious cognitive deficits, such as dementia, a progressive deterioration of memory and other aspects of cognitive function.
Seven types of normal memory problems
Regardless of age, healthy people can experience memory loss or memory distortion. Daniel Schacter, a professor of psychology at Harvard University, describes seven common "sins" of memory, discussed below. Some of these memory flaws become more pronounced with age, but — unless they are extreme and persistent — they are not considered indicators of Alzheimer's or other memory-impairing illnesses.
Transience
This is the tendency to forget facts or events over time. You are most likely to forget information soon after you learn it. However, memory has a use-it-or-lose-it quality: memories that are called up and used frequently are least likely to be forgotten. Although transience might seem like a sign of memory weakness, brain scientists regard it as beneficial because it clears the brain of unused memories, making way for newer, more useful ones. In this sense, transience is akin to cleaning the junk out of your closets or clearing the temporary files from your computer's hard drive.
Although everyone experiences transience of memory, it is extreme and debilitating in people with particular kinds of brain damage. For instance, people with amnesia from damage to the hippocampus and related structures have normal short-term memory, but they are unable to form new long-term memories (see "Amnesia: Memory loss caused by injury or trauma"). They forget information soon after they learn it.
Absentmindedness
This type of forgetting occurs when you don't pay close enough attention. You forget where you just put your pen because you didn't focus on where you put it in the first place. You were thinking of something else (or, perhaps, nothing in particular), so your brain didn't encode the information securely. Absentmindedness also involves forgetting to do something at a prescribed time, like taking your medicine or keeping an appointment.
One way to avoid this problem is to identify things that can serve as cues to remind you to do something. For example, if the doctor tells you to take your medicine at bedtime, you might use another regular bedtime activity as a reminder cue for medicine-taking. In this situation, you could link rinsing after tooth brushing and use the same water glass to sip water to take your pills. Similarly, if you need to take your vitamins at breakfast, you could make a habit of putting the bottle beside your coffee cup at your place at the table so they'd provide a cue when you sit down to eat.
Blocking
Someone asks you a question and the answer is right on the tip of your tongue — you know that you know it, but you just can't think of it. This tip-of-the-tongue experience is perhaps the most familiar example of blocking, the temporary inability to retrieve a memory. Blocking doesn't occur because you weren't paying attention or because the memory you're looking for has faded from your brain. On the contrary, blocking occurs when a memory is properly stored in your brain, but something is keeping you from finding it.
In many cases, the memory block is a memory similar to the one you're looking for, and you retrieve it instead of the one you want. This competing memory is so intrusive that you can't think of the memory you want. A common example is if you call your older son by your younger son's name, or vice versa. Scientists call blocking memories "ugly stepsisters" because they're domineering, like the stepsisters in Cinderella. Scientists have used ugly stepsisters experimentally to block memories. In one such experiment, people were asked to pick out the definitions of uncommon words from a selection of possible definitions. When definitions that were similar in sound or in meaning were given along with the accurate definition, more people had memory blocks than when unrelated ones were given.
Brain-imaging studies suggest how blocking might work in the brain. When a person is retrieving a memory, some regions of the brain become more active and others become less active. Some of the increased activation reflects inhibition. When the right regions are activated, the inhibition of other regions can work in your favor by keeping your brain from calling up irrelevant information. But when you call up an ugly stepsister by mistake, the brain regions that encode it may suppress the regions needed to retrieve the memory you really want.
Scientists think that memory blocks become more common with age and that they account for the trouble older people have remembering other people's names. But it remains unclear whether tip-of-the-tongue experiences are more common than other age-related memory problems. Nor have researchers determined whether memory blocks are simply caused by the overall slowing of memory retrieval that occurs with age. In any case, there's encouraging news about blocking. Research shows that people are able to retrieve about half of the blocked memories within just a minute.
Misattribution
Consider the following scenario: you're asked who "John Smith" is, and you remember quite clearly not only who he is, but also what he's done lately that's been in the news. Then you're asked where you learned these details. You think for a moment and reply that it was on the evening TV news. However, there was no report about John Smith on TV. Instead, you got your information from the friend you had lunch with yesterday.
Right memory, wrong source — that's one example of misattribution. Misattribution occurs when you remember something accurately in part, but misattribute some detail, like the time, place, or person involved. Another kind of misattribution occurs when you believe a thought you had was totally original when, in fact, it came from something you had previously read or heard but had forgotten about. This sort of misattribution explains cases of unintentional plagiarism, in which a writer passes off some information as original when he or she actually read it somewhere before.
Misattribution happens to everyone. Usually it's harmless, but it can have profound consequences, particularly in the criminal justice system. In some cases, misattribution on the part of eyewitnesses is responsible for the arrest and conviction of individuals for crimes they didn't commit.
As with several other kinds of memory lapses, misattribution becomes more common with age. Age matters in at least two ways. First, as you age, you absorb fewer details when acquiring information because you have somewhat more trouble concentrating and processing information rapidly. Second, as you grow older, your memories grow older as well. And old memories are especially prone to misattribution.
Suggestibility
Imagine that you saw someone fleeing from a car as its antitheft alarm was blaring. You didn't get a good look at the thief, but another person on the street insisted that it was a man wearing a green plaid jacket. Later, when the police show you photos of possible suspects, you're confused until you see a man dressed in green plaid. Then you point to him.
Suggestibility is the vulnerability of your memory to the power of suggestion — information that you learn about an occurrence after the fact. Although little is known about exactly how suggestibility works in the brain, the suggestion fools your mind into thinking it's a real memory. Suggestibility can be the culprit in recollections that adults have of incidents from their childhood that never really happened (see "Are recovered memories real?" below).
Bias
One of the enduring myths about memory is that it works like a camera, recording what you perceive and experience with complete, objective accuracy. But even the sharpest memory isn't a flawless snapshot of reality. In your memory, your perceptions are filtered by your personal biases — experiences, beliefs, prior knowledge, and even your mood at the moment. Your biases affect your perceptions and experiences when they're being encoded in your brain. And when you retrieve a memory, your mood and other biases at that moment can influence what information you actually recall.
Bias can affect all sorts of memories, but among the most interesting examples are people's recollections of their romantic relationships. In one study, couples who were dating were asked to evaluate themselves, their partners, and their relationships — initially and then two months later. During the second session, participants were asked to recall what they had said initially. The people whose feelings for their partners and their relationships had become more negative over time recalled their initial evaluations as more negative than they really were. On the other hand, people whose feelings for their partners and their relationships had become more loving recalled their initial evaluations as more positive than they really were.
Although everyone's attitudes and preconceived notions bias their memories, there's been virtually no research on the brain mechanisms behind memory bias or whether it becomes more common with age.
Persistence
Most people worry about forgetting things. But in some cases people are tormented by memories they wish they could forget, but can't. The persistence of memories of traumatic events, negative feelings, and ongoing fears is another form of memory problem. Some of these memories accurately reflect horrifying events, while others may be negative distortions of reality.
Two groups of people are particularly prone to having persistent, disturbing memories. One group is individuals with depression. Research has shown that depressed people are given to ruminating over unpleasant events in their lives or mistakes that they believe they have made. Dwelling on such negatives also fuels a vicious cycle of increasing depression. The other group with persistent, unwanted memories includes people with post-traumatic stress disorder (PTSD). PTSD can result from many different forms of traumatic exposure — for example, sexual abuse or wartime experiences. Flashbacks, which are persistent, intrusive memories of the traumatic event, are a core feature of PTSD (see "Post-traumatic stress disorder").
Are recovered memories real?Recovered memories are vivid, emotionally powerful recollections of events or occurrences from the distant past that a person has not thought of in years. These memories are frequently recovered in the course of psychotherapy. The use of such memories — in particular, as evidence of past child abuse, incest, or other traumatic events — has engendered considerable controversy. Critics of the concept of recovered memory point out that memory is not a literal register of experience. What we remember — and how we remember it — is influenced by our personalities, as well as our beliefs, hopes, and needs. New experiences interact with old memories and cause them to distort or decay, and we may fill in the gaps, merge the memories of several events, or confuse what we had imagined or heard about with what we actually witnessed or experienced. Just the act of trying to remember an event can confuse suggestion with reality. Pioneering research in this area was the so-called "Lost in the Mall" study published in 1995. Participants were told three stories about their childhoods allegedly gathered from family members. In reality, only two of the incidents actually took place. The third was a fabricated account of the individual having been lost in a shopping mall at age 5. When prompted to remember the events, 25% of the subjects said they recalled being lost in the mall even though the incident never took place. Many embellished the story beyond the narrative supplied by the researchers. Subsequent variations on the study conducted in the intervening years have shown that some subjects can be prompted into adopting even more implausible fictional memories such as having taken a hot air balloon ride or having been attacked by a wild animal. Critics of recovered memory charge that these recollections often reflect the power of suggestion during psychotherapy sessions and that the therapist, an authority figure, can inadvertently play a key role in encouraging false memories to form. Similarly, when the memory of distant events is a vital aspect of a criminal investigation, police, social workers, and other officials can intentionally or unintentionally influence what a person remembers. Champions of the recovered memory concept, on the other hand, insist that the more unusual and disturbing the memory, the less likely it is to be false. If anything, they say, people tend to doubt recovered memories of child abuse more than they should. Advocates say that most recovered memories are spontaneous and are not generated as the result of a therapist's intervention, although they may be revealed in that context because the therapist creates a safe environment in which to disclose them. Both sides in this dispute have tried to support their positions with evidence from cognitive neuroscience, including animal experiments, brain scans, neuropsychological tests, and the examination of brain-damaged patients. The majority of mental health professionals take a position between the two extremes. Although there is no established consensus, we know that memories can contain varying elements of truth, partial truth, or distortion, and individuals have different capacities for remembering and forgetting. A true memory (recovered or persistent) cannot be distinguished from a false one on the basis of internal evidence alone. Instead, people must tolerate some uncertainty. As further research clarifies the subtle nuances of how normal memory works, scientists may better understand the interplay between knowledge and emotion in the recollection of traumatic experiences. |
Review Date: 2008-05-01
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