Forgetting: What’s normal?
(This article was first printed in the
Harvard Health Publications Special Health
Report “Improving Memory: Understanding
and Preventing Age-Related Memory Loss”.
For more information or to order, please
go to http://health.harvard.edu/IM.)
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 more physically
coordinated. 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.
types of normal memory problems
Regardless of age, healthy people can experience
memory loss or memory distortion. In a book,
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.
This is the tendency to forget facts or events
over time. You are most likely to forget information
soon after you learn it; as time passes, the
likelihood of forgetting decreases. 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”).
They forget information soon after they learn
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. In this case, the
problem is that you didn’t focus on things
that can serve as cues to remind you to do
something — like putting your vitamin
pills at your place at the table so you’ll
remember to take one when you eat breakfast.
For example, if the doctor told you to take
your medicine at bedtime and you forgot to
do so, it could be that you didn’t pay
close enough attention to the key word: bedtime.
If you had, chances are that certain details
of your bedtime routine (like brushing your
teeth or watching a particular show on TV)
would have served as cues to remind you to
take your medicine.
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
but one that you retrieve instead. This other
memory is so intrusive that you can’t
think of the memory you want. A common example
is if you call your older daughter by your
younger daughter’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.
Scientists interpret this finding to mean that
the active regions actually inhibit the other
regions. 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.
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.
The older the memory, the more likely it is
to suffer misattribution. One study documented
how misattribution crept into people’s
recollections of the explosion of the space
shuttle Challenger. Immediately after the Challenger
tragedy, researchers at Emory University asked
students to write down what they were doing
when they heard the news. A year later, the
researchers asked the same students to write
down their memories of the event again. These
later descriptions were riddled with misattributions.
But misattributions can be startlingly strong.
When told of the discrepancies, the students
had trouble believing that their memories were
inaccurate. Indeed, three years later, when
the students were once again asked to recall
the Challenger explosion, their recollections
were closer to their second accounts.
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. Second, as you grow
older, your memories grow older as well. And
old memories are especially prone to misattribution.
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
Suggestibility refers to false memories that
you develop because someone or something gives
you some key information at the same time that
you’re trying to retrieve a memory. Although
little is known about exactly how suggestibility
occurs in the brain, the suggestion fools your
mind into thinking it’s a real memory.
Suggestibility is the culprit in memories that
adults have of incidents from their childhood
that never really happened (see “Are
recovered memories real?”).
In several studies, people have been induced
to recall false events from their childhood
after a researcher planted ideas in their minds.
In one study, college students’ parents
were asked to complete a questionnaire that
asked whether certain events happened to the
students. Then the students themselves were
asked whether they recalled several events — some
of which had actually happened (according to
the parents’ responses) and some of which
hadn’t. At first, 80%–90% of the
students accurately recalled the events that
had and hadn’t happened to them. But
in later interviews, if a researcher suggested
that a false event had actually happened to
them when they were children, 20%–40%
of the students described some memory of it.
No one knows whether people become more vulnerable
to suggestibility as they age, but studies
have demonstrated that many children experience
it when asked to recollect alleged incidents
of sexual abuse. Several studies with preschoolers
indicate that suggestive questioning by the
police or other adults can lead children to
assert that certain events occurred when in
fact they didn’t.
One of the biggest myths about memory is that
it works like a camera, recording what you
learn with complete accuracy. But even the
sharpest memory isn’t a flawless snapshot
of reality. In your memory, reality is filtered
by your personal biases — experiences,
beliefs, prior knowledge, and even your mood
at the moment. Your biases affect your memories
when they’re being encoded in your brain.
And your mood and other biases at the moment
when you retrieve a memory can influence what
information you actually call up.
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 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 they become more
common with age.
Most people worry about forgetting things.
But in some cases people wish they could forget,
but can’t. The persistence of memories
about traumatic events, negative feelings,
and chronic 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 especially prone
to having persistent, upsetting 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 is a condition that can
result from many different sorts of traumatic
events — for example, sexual abuse or
wartime experiences. Flashbacks, which are
persistent, intrusive memories of the traumatic
event, are a core feature of PTSD.
Research has shown that persistent memories
depend on the activation of those parts of
the brain that respond to fear, anxiety, and
emotionally charged information. Brain-imaging
studies have shown that when people with PTSD
recall a persistent, intrusive memory, there
is activity in the amygdala as well as in other
regions associated with the experience of fear
and anxiety. Many people learn to control persistent
memories through therapy that involves guided
imagery, or visualization. With this technique,
a therapist helps the patient learn gradually
to envision the traumatic incident without
intense fear, eventually lessening PTSD symptoms.
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.
The use of such memories — in
particular, as evidence of past child
abuse, incest, or other traumatic events — has
engendered considerable controversy.
Critics of recovered-memory therapy
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
interfere 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.
Critics charge that recovered memories
often reflect the power of suggestion
during psychotherapy sessions and that
the therapist, an authority figure,
plays the key role in encouraging such
false memories to emerge. 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 recovered memory, 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 longer 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
Both sides in this dispute have tried
to support their positions with evidence
from neurology and cognitive neuroscience,
including animal experiments, brain
scans, neuropsychological tests, and
the examination of brain-damaged patients.
But the majority of mental health professionals
take a position between the two extremes.
Although there is no established consensus,
the following advice may be useful.
There are many degrees and several
kinds of forgetting. Memories can contain
varying elements of truth, partial
truth, or distortion, and different
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. More research is needed
on the prevalence of false memories
and delayed recall. Eventually, as
research clarifies the subtle nuances
of how normal memory works, scientists
may gain a better understanding of
the interplay between knowledge and
emotion in the recollection of traumatic
experiences and may reach a consensus
on the usefulness and reliability of