'We can implant entirely false memories'
You were abducted by aliens, you saw Bugs Bunny at Disneyland, and then you went
up in a balloon. Didn't you? Laura Spinney on our remembrance of things past
Thursday December 4, 2003
The Guardian
Alan Alda had nothing against hard-boiled eggs until last spring. Then the
actor, better known as Hawkeye from M*A*S*H, paid a visit to the University of
California, Irvine. In his new guise as host of a science series on American TV,
he was exploring the subject of memory. The researchers showed him round, and
afterwards took him for a picnic in the park. By the time he came to leave, he
had developed a dislike of hard-boiled eggs based on a memory of having made
himself sick on them as a child - something that never happened.
Alda was the unwitting guinea pig of Elizabeth Loftus, a UCI psychologist who
has been obsessed with the subject of memory and its unreliability since Richard
Nixon was sworn in as president. Early on in her research, she would invite
people into her lab, show them simulated traffic accidents, feed them false
information and leading questions, and find that they subsequently recalled
details of the scene differently - a finding that has since been replicated
hundreds of times.
More recently, she has come to believe that lab studies may underestimate
people's suggestibility because, among other things, real life tends to be more
emotionally arousing than simulations of it. So these days she takes her
investigations outside the lab. In a study soon to be published, she and
colleagues describe how a little misinformation led witnesses of a terrorist
attack in Moscow in 1999 to recall seeing wounded animals nearby. Later, they
were informed that there had been no animals. But before the debriefing, they
even embellished the false memory with make-believe details, in one case
testifying to seeing a bleeding cat lying in the dust.
"We can easily distort memories for the details of an event that you did
experience," says Loftus. "And we can also go so far as to plant entirely false
memories - we call them rich false memories because they are so detailed and so
big."
She has persuaded people to adopt false but plausible memories - for instance,
that at the age of five or six they had the distressing experience of being lost
in a shopping mall - as well as implausible ones: memories of witnessing demonic
possession, or an encounter with Bugs Bunny at Disneyland. Bugs Bunny is a
Warner Brothers character, and as the Los Angeles Times put it earlier this
year, "The wascally Warner Bros. Wabbit would be awwested on sight", at Disney.
Elizabeth Loftus' research has obvious implications for the reliability of
eyewitness testimony. And it was as a result of her findings that in 1994 she
co-wrote her book, The Myth of Repressed Memory, and took a strong stand in the
recovered memory debate of the 90s, for which she was reviled by those who
claimed to have uncovered repressed memories of abuse - alien, sexual or
otherwise.
The American Psychological Association (APA) now takes the line that most people
who were sexually abused as children remember all or part of what happened to
them, and that it is rare (though not unheard of) that people forget such
emotionally charged events and later recover them. But it states that,
"Concerning the issue of a recovered versus a pseudomemory, like many questions
in science, the final answer is yet to be known." And the debate simmers on.
Several new lines of evidence suggest that the interaction between memory and
emotion is more complex than was thought. Powerful emotions, it seems, can both
reinforce and weaken real memories. We may be able to actively degrade painful
memories. And false memories, once accepted, can themselves elicit strong
emotions and thereby mimic real ones.
To try to tease apart these complex relationships, the psychologist Daniel
Wright and his colleagues at the University of Sussex have been looking into
what it is that makes some people more susceptible to false memories than
others. On average, studies show that around a third of those subjected to the
"misinformation effect" wholly or partially adopt a false memory, but it seems
to depend on both the person and the memory. Alan Alda swallowed the hard-boiled
egg story, to the extent that he declined to eat one at the UCI picnic, but he
wasn't taken in by Bugs Bunny in Disneyland. In one study published last year,
50% of volunteers were persuaded they had taken a ride in a hot-air balloon when
they had not. But when Kathy Pezdek of the Claremont Graduate University,
California, tried to make people believe they had received a rectal enema, she
met with almost universal resistance.
Amid all this variability, Wright's group did find one significant correla tion
- though it was not dramatic: those who were more vulnerable to false memories
also tended to suffer more frequent lapses in attention and memory. The trouble
is, he says, "People who have been traumatised also tend to score higher on
tests of lapses in memory." Their traumatic experiences may contribute to their
forgetfulness, but their forgetfulness may lay them open to memory distortion -
so true and false become harder to disentangle.
Among the symptoms suffered by victims of post-traumatic stress disorder (PTSD)
are chilling flashbacks. But, says Michael Anderson of the University of Oregon,
"People who suffer PTSD represent a very small fraction of the people who
experience trauma. The great majority of people who experience trauma never
develop PTSD and eventually are able to adapt in the face of these events." He
argues that they do so by suppressing the memory, and that this suppression
gradually erases it.
Two years ago, Anderson's group showed that people who deliberately try to keep
a word out of their mind find it harder to recall later than if they had not
suppressed it. Counter- intuitively, this form of forgetting seems more likely
to occur when people are confronted by reminders of the very memory they want to
avoid. Anderson says an extreme example of this might be a child who is forced
to live with an abusing care-giver, and must put the memory of abuse to one side
in order to interact with that care-giver. "If people continue to work at it,
the amount of forgetting grows with repetition and time," he says.
At the annual meeting of the US Society for Neuroscience in New Orleans last
month, Anderson's group presented new data on how this "motivated forgetting"
might arise in the brain. When people tried to suppress memories for certain
words while having their brains scanned in a magnetic resonance imaging machine,
not only did the researchers see a dampening of activity in the hippocampus, a
structure known to be critical for memory formation, but the frontal cortex was
highly active. Since the frontal cortex is important for conscious control, they
believe that neurons here may be suppressing the representation of the unwanted
word in the hippocampus, and in the process impairing its memory.
However, Anderson admits that his experiments ignore the effect of a memory's
emotional intensity on a person's ability to suppress it. And there is plenty of
evidence that memory for emotionally charged events can be enhanced - albeit at
a cost. Also last month, Bryan Strange of the Wellcome department of imaging
neuroscience at University College London and colleagues showed that people were
more likely to remember a word if it was emotionally arousing - "murder" or
"scream", say - than if it was neutral. And the words most likely to be
forgotten were neutral ones presented just before emotionally arousing ones. The
effect was more pronounced in women than in men, and both the enhanced memory
for the emotional word and the forgettability of the preceding neutral one could
be reversed by dosing the volunteers in advance with the drug propranolol.
Propranolol, a commonly prescribed beta-blocker, interferes with the
neurochemical pathway thought to be responsible for making emotionally arousing
events more memorable - the beta-adrenergic system - and it has already been
used experimentally in the treatment of patients with PTSD. In one study,
published in October, Guillaume Vaiva of the University of Lille and colleagues
offered prop- ranolol to victims of assault or motor accidents shortly after
their traumatic experience, and then invited them back for psychological testing
two months later. On their return, almost all the patients exhibited some
symptoms associated with PTSD, but they were twice as severe among those who had
not taken the drug.
The finding that propranolol can be effective at blocking memory when given
after an event as well as before is important because, as Loftus explains, "In
the real world you can't be there to exert your manipulations right at the time
an event is happening, but you can get on the scene later." It has been proposed
that propranolol should be offered to victims of rape as a standard measure to
prevent them developing PTSD. But could it also be used to erase false memories
- for instance, "recovered" memories of alien abduction - that nevertheless
elicit all the physiological responses associated with harrowing, real memories?
"If the formation of false memories depends on beta-adrenergic activation, then
it would seem very possible that propranolol administration could affect them,"
says the UCI neuro- biologist Larry Cahill, who has also investigated the
effects of the drug in PTSD patients. But Ray Dolan of UCL, a co-author with
Bryan Strange of the study on memory for emotional words, points out that not
all false memories have a common basis. If they are interpolations into gaps in
memory, such as the gap that opened up before the presentation of an emotionally
arousing word, or possibly the gap into which Alan Alda inserted a memory of
having over-indulged in eggs, then it is conceivable the drug would work. But,
says Dolan, "Other classes of false memory, for example, where the memories are
fantasies or out-and-out fabrications, would be immune to propranolol."
The idea of doctors having the power to wipe the memory clean sends shivers down
many people's spines. False memories could safely be erased, perhaps, assuming
there was a reliable way of differentiating them from true ones. Although
brain-imaging techniques highlight some differences in patterns of brain
activation when a person recalls a true as opposed to a false memory, these are
statistical differences only. "We are so far away from being able to use these
techniques to reliably classify a single memory as being real or not real," says
Loftus, "Yet that is what the courts have to do."
True memories, too, can get out of control and become destructive, leading to
PTSD and other anxiety disorders. But they start out as an important
self-defence mechanism - teaching you, for instance, that too many hard-boiled
eggs are bad for you. Erasing them completely could be dangerous.
In the end, says Loftus, it will come down to personal choice. "What would you
rather be in the world, sadder but wiser, all too well remembering the horrors
of your past and feeling depressed, or perhaps not remembering them very much
and being a little happier?"
Further reading
The Myth of Repressed Memory by Dr Elizabeth Loftus and Katherine Ketcham, 1996
paperback (St Martin's Press, New York). ISBN 0312141238
American Psychological Association website with links to questions and answers
about memories of childhood abuse: www.apa.org/pubinfo/
Suppressing unwanted memories by executive control by Michael C Anderson and
Collinn Green, Department of Psychology, University of Oregon, 2001 (Nature, 410
[6826], 366-9)