Déjà vu: Where fact meets fantasy
25 March 2009
by
Helen Phillips
Mr P, an 80-year-old Polish émigré and former engineer, knew he had
memory problems, but it was his wife who described it as a permanent
sense of déjà vu. He refused to watch TV or read a newspaper, as he
claimed to have seen everything before. When he went out walking he
said the same birds sang in the same trees and the same cars drove past
at the same time every day. His doctor said he should see a memory
specialist, but Mr P refused. He was convinced that he had already been.
Déjà
vu can happen to anyone, and anyone who has had it will recognise the
description immediately. It is more than just a sense that you have
seen or done something before; it is a startling, inappropriate and
often disturbing sense that history is repeating, and impossibly so.
You can't place where the earlier encounter happened, and it can feel
like a premonition or a dream. Subjective, strange and fleeting, not to
mention tainted by paranormal explanations, the phenomenon has been a
difficult and unpopular one to study.
Now
that is changing, spurred in part by Mr P and a handful of people who,
like him, have dementia and experience continuous déjà vu, and also by
the discovery that there is a group of people with epilepsy who have
déjà vu-like auras before a seizure. They are making it possible for
researchers to catch the process in action, bringing hope that the
secrets of this strange and disturbing phenomenon could finally be
unlocked. Surprisingly, not only is déjà vu proving an interesting
window on the peculiar ways that our memory works, it is also providing
a few clues about how we tell the difference between what is real,
imagined, dreamed and remembered - one of the true mysteries of
consciousness.
Speculations
about past lives or telepathy aside, the first biological explanations
of déjà vu were based on ideas that two sensory signals in the brain -
perhaps one from each eye or each hemisphere of the brain - for some
reason move out of sync, so that people have the experience of reliving
the same event. "Mental diplopia", as it was called, is intuitively
appealing but the evidence is stacked against it. Information from the
two eyes mixes very early in visual processing, long before we perceive
a scene. What's more, déjà vu - rather ironically as the term means
"already seen" - can occur in blind people, according to Chris Moulin,
a psychologist at the University of Leeds, UK, (Brain and Cognition,
vol 62, p 264). Then there are the cases of people who have had their
two cortical hemispheres surgically separated in an attempt to relieve
intractable epilepsy. If the mental diplopia idea were correct you
might expect them to have permanent déjà vu, yet there are no reports
of this happening.
A
second intuitive explanation is some sort of distortion in time
perception. Somehow, incoming signals must get misinterpreted and
labelled with an inappropriate time stamp, making the experience seem
old as well as current. If the brain's memory system is like a tape
recorder, it is as if the recording head has got muddled with the
playback head. It is an interesting analogy, but it does not appear to
have any anatomical basis in the brain.
Now
another theory is gaining credibility. Perhaps déjà vu feels like
reliving a past experience because we actually are - at least to some
extent. Psychologist Anne Cleary of Colorado State University in Fort
Collins came to this idea via an interest in memory problems. Keen to
explain instances such as when something seems to be on the tip of the
tongue, or when we recognise a face but can't place it, she started
looking for parallels with déjà vu. "One particular theory of déjà vu
is that it may be a memory process," she says. "Features of a new
situation may be familiar from some prior situation."
Her
first experiments seem to support this. In one, she was able to induce
familiarity for images of celebrity faces or well-known places, even if
the viewer couldn't place the image, simply by first presenting
subjects with lists of their names. In another study volunteers
reported familiarity with words that sounded similar to ones presented
in an earlier list. Nevertheless, Cleary acknowledges that this can't
be the whole story. "Déjà vu is unique in that it is not just another
instance of familiarity, it actually feels wrong," she says.
How
to account for this? One possibility is that déjà vu is based on a
memory fragment that comes from something more subtle, such as
similarity between the configuration or layout of two scenes. Say you
are in the living room of a friend's new house with the eerie feeling
that you have been there before, yet knowing you can't possibly. It
could be just that the arrangement of furniture is similar to what you
have seen before, suggests Cleary, so the sense of familiarity feels
misplaced.
To
test the idea, her team produced a large range of images showing scenes
such as a bar, a bowling alley, landscapes or rooms from a house.
Volunteers saw a subset of these, then they were tested on a new set,
half of which were entirely novel and the other half resembling scenes
from the first set in structure and configuration but not content. Not
only did the similar layouts produce familiarity without recall,
subjects also reported a sense of the inexplicable, having been told
that all the scenes were different.
Although
the familiarity idea appeals to many, Moulin, for one, is not
convinced. His scepticism stems from a study of a person with epilepsy
that he conducted with Akira O'Connor, now at Washington University in
St Louis, Missouri. This 39-year-old man's auras of déjà vu were
long-lasting enough to conduct experiments during them. The researchers
reasoned that if familiarity is at the root of déjà vu, they should be
able to stop the experience in its tracks by distracting the man's
attention away from whatever scene he was looking at. However, when he
looked away or focused on something different, his déjà vu did not
dissipate, and would follow his line of vision and his hearing,
suggesting that real familiarity is not the key. The fact that an
epilepsy aura can cause déjà vu at all suggests that it is erroneous
activity in a particular part of the brain that leads to misplaced
feelings of familiarity, suggests Moulin.
Hypnotic dissociation
But
how? Moulin and O'Connor think déjà vu is the consequence of a
dissociation between familiarity and recall. We know that we can have a
sense of familiarity for a face or name without actually remembering
where we know it from. Using hypnosis, O'Connor and Moulin have been
able to create a more mysterious sense of familiarity that leads people
to draw parallels with déjà vu. One group of people was given a puzzle
to solve. Then, while under hypnosis, they were told they would be
given the puzzle again, but would not recall it. Another group did not
do the puzzle but were told under hypnosis that they would be given it
later and that they would experience feelings of familiarity but not
understand why. Both situations produced a sense of eerie familiarity,
which some people likened to déjà vu. Moulin and O'Connor hope that
their ability to induce a déjà vu-like state in the lab will help them
probe the phenomenon. They also believe these experiments support the
idea that familiarity and recall are dissociable, and that you can have
a sense of familiarity without actually having any prior experience of
something.
Studies
of the brain also support the idea that separate circuits mediate
recollection and familiarity, according to John Aggleton and Malcolm
Brown of Cardiff University, UK, who recently reviewed brain imaging
and animal studies (Trends in Cognitive Sciences, vol 10, p 455).
They point out that different parts of the medial temporal lobe, at the
side of the brain, are responsible for different aspects of memory
recall (see illustration). The
curved tube-like hippocampus, which runs through the centre of the
lobe, mediates recollection, particularly of autobiographical memories.
Meanwhile, the studies show that the surrounding parahippocampus,
particularly the perirhinal cortex, may provide the feelings of
familiarity.
This
fits well with the evidence from brain scans of Mr P and others like
him, who show huge degeneration of neurons in the medial temporal lobe,
and the fact that it is epilepsy originating in the medial temporal
lobe that leads to déjà vu auras.
It
is possible that both Moulin and Cleary are correct. The perirhinal
cortex may store information about spatial relationships, rather than
time, place and sequence of events, and so normal familiarity feelings
could come largely from layout and configuration, backing Cleary's
findings. Indeed, there may be many ways to produce false familiarity,
according to psychologist Alan Brown of Southern Methodist University
in Dallas, Texas, author of The déjà vu experience (Psychology
press, 2004). His own experiments indicate some other possibilities.
For example, he has induced the feeling by distracting volunteers while
they saw a glimpse of a scene and then moments later giving them a good
look. "If you take a brief glance when distracted, and look at the same
scene again afterwards, it can feel like you've seen it before but much
earlier," says Brown. He has also induced it by showing people images
of things they had forgotten. "Just as a stomach ache can hurt the same
way but be caused by lots of different processes, it could be the same
way with déjà vu," he says.
The
real problem with explaining déjà vu, however, is not how we can get
familiarity without recognition, but why it feels so disturbing. "We'd
get it all the time if it were just familiarity with real experiences,"
says Ed Wild from the Institute of Neurology in London. He suggests
that mood and emotion are also important contributors to the sensation
of déjà vu. We need the right combination of signals, not just the
layout of a scene but how we feel at the time, to believe something is
familiar when really it is not.
A matter of degree
Moulin
agrees it may be matter of degree. The regions thought to mediate
recall, familiarity and emotions are all extremely closely linked. A
small amount of stimulation could produce a mild sense of familiarity,
while a stronger stimulus could spread into neighbouring emotion
regions producing a more disturbing feeling, or even the striking sense
of doom or premonition some people report with déjà vu.
Cognitive
neuroscientist Stefan Köhler from the University of Western Ontario in
London, Canada, believes the role of emotion is even more central in
generating the sense of weirdness that accompanies déjà vu. He recently
had the chance to image the brain of a person cured of epilepsy with
déjà vu auras by removal of a large tumour that was triggering the
seizures. The excised areas consisted of parts of the hippocampus and
perirhinal cortex, but also included the amygdala. It suggests that
this region, which is known to be heavily tied up with emotion, was
also involved in creating the déjà vu. Köhler speculates that without
the appropriate emotional arousal, perhaps the brain cannot recognise a
person or place we have encountered before as truly familiar. On the
other hand, inappropriate emotional arousal may make us believe
something is familiar when actually it is not.
The
final element of déjà vu, a sense that it feels impossible, probably
comes from the reasoning parts of our brain. According to Köhler, when
our rational knowledge tells us one thing, but our emotional instincts
tell us another, it can feel very wrong. This final element is missing
in people with dementia, including Mr P, who accept their experiences
as perfectly normal. Köhler suspects this may be because
neurodegeneration in these individuals has caused a disconnection
between the temporal lobes, which are generating sensations, and the
frontal lobes which are continuously interpreting them.
Our
brains are looking for associations all the time. Déjà vu is
interesting, says Kohler, because it points to a brain mechanism that
helps you interpret what you are doing. When you are having a memory,
you have the sensation of recollection. It feels like having a memory,
and doesn't feel like daydreaming or current reality. "Déjà vu is a
fault in a kind of cognitive process that is going on in the background
all the time. When it goes wrong, it's very striking," says Moulin. At
the extreme, patients with permanent déjà vu - dubbed déjà vecu, for
already experienced - actually make up stories to make sense of it (New
Scientist, 7 October 2006, p 32).
While
déjà vu is starting to divulge some of its secrets, there is still a
long way to go before we understand how we actually decide what is
real, imagined, dreamed or experienced, and how these various tags lead
to such different conscious experiences. One anecdotal finding that
came to light while working on this article is that people who think a
lot about déjà vu are more prone to it. I had déjà vu about reading
about déjà vu, and researchers have had déjà vu about having déjà vu.
It certainly retains mystery enough to justify further study. After
all, says Wild, "déjà vu is one of weirdest brain experiences that
normal people have".
Stranger and stranger yet
About 10 per cent of people
claim never to have experienced déjà vu, while some individuals report having
it regularly.
Children first get it at around
age 8 or 9, suggesting that a degree of cognitive maturity is required.
Déjà vu happens less as you get
older and more when you are tired, anxious or stressed.
It
is particularly prevalent in people with certain conditions known to
produce problems in time perception, such as schizophrenia and epilepsy.
Although
there is no gene for déjà vu, it is possible that certain versions of
genes associated with epilepsy make some of us more prone to it.
Just reading this article could
give you déjà vu.
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