- Hi, I'm Dr. Tracey Marks, a psychiatrist
and I make mental health education videos.
Today, I'm answering a viewer question,
to talk about déjà vu.
I decided to add in information
about delusional misidentification
because it's a similar phenomenon
but taken to a different level.
Déjà vu is French for the term already seen.
Déjà vu is the misperception that something new is familiar.
It can be a place that you go to
and feel like you've been there before,
even though you can't recall any details of the experience.
So it's not as though you say to yourself,
oh yeah I recognize that red building,
so I know I must have been here before.
You don't recognize anything.
It's more of the sense, or just this feeling
that you've been here before or experienced it before.
It can be a person that you think you've seen before
or a conversation that you feel like you've had.
And this is a very common phenomenon
and it's related to familiarity-based recognition.
The ability to recognize something
that you've experienced before,
is thought to be predominantly controlled
by your hippocampus, which is responsible
for other types of memory functions.
We don't know exactly why this happens in people
who don't have an illness or a disorder,
but it's hypothesized that it's a glitch in the system
where your brain incorrectly matches an experience
from a previous memory that's similar
and feeds the information to you
and gives you the feeling that, oh yeah
I've experienced this before,
when you really haven't.
It's something similar
to what you're currently experiencing.
Most times it comes and goes
and it's not a lingering problem that causes distress.
There are conditions though, that can make it happen more.
Frequent episodes of déjà vu can happen
with temporal lobe epilepsy.
And this is where you have abnormal firing
of the nerves in your temporal lobe.
Your hippocampus is located in your temporal lobe.
We have seen some link between episodes of déjà vu
and anxiety and depression.
Brain scans have shown decreased hippocampal volume
in people who have depression,
similar to the brain volume loss in people with epilepsy.
So there are some data to suggest
that if you have depression or anxiety
you may be more prone to experience this
but it would still be occasional
and not a predominant experience.
So that's déjà vu, a random misapplication
of your familiarity recognition ability.
A more pathological problem identifying what's familiar
and unfamiliar occurs
with delusional misidentification syndromes.
These are a group of delusional disorders
that involve a problem with familiarity.
The four syndromes are Capgras delusions,
Fregoli delusions, intermetamorphosis syndromes
and syndrome of subjective doubles.
Capgras delusion is where a person believes
that someone close to them has been replaced
by a double or an imposter.
This is an example of hypo-familiarity,
you don't recognize your loved one as being familiar to you.
So you think that it's a stranger
that you've never met before.
Fregoli delusion has the opposite problem.
with this you're hyper-familiar,
you believe that your loved one has been reincarnated
into other people.
So for an example, you may see a stranger
and insist that it's your mother.
And because of this, you act inappropriately
with the person.
Intermetamorphosis occurs when you believe
that someone familiar to you
has changed into someone else familiar.
So you can see your husband as really being your brother.
And it's fascinating how the mind works with this.
I've talked to someone with this delusion
and you may think, well, can't the person just tell
that this person looks nothing like who they think it is?
So in this case, what the person sees,
or saw visually had no bearing on what the belief was
because this is a delusion
and the delusion is not based on gathering data
and then coming to a conclusion.
It's based on a delusional belief
that this is a familiar person
but the person is different from who they think it is.
So it doesn't matter that she saw
that the person right in front of her was much taller
and completely different build and different look,
it's almost as though she couldn't even see that part.
And when challenged on these details,
she would make up a story, or it's as though
she could fill in the blanks with explanations,
like, well, he looks tall but my husband's tall too.
You know, just kind of things that help support
the belief that's fixed in her head.
It's a very strongly driven
belief that has very little to do
with what the person actually sees.
The last delusion
in this quadrad of delusions,
is subjective doubles.
And this is the belief that you have a doppelganger
or identical double of yourself living an alternate life.
And this is part of the basis of the movie "Us.
However, in that movie, that wasn't one person's belief.
It was the way of the world,
that there was a separate alternate life
or group of people that were identical doubles of yourself.
With this delusion, you're the only person
that believes that.
All of these delusions are fairly rare,
but they are often associated with a neurological disorder
like Lewy body dementia or Alzheimer's disease.
It's also thought that unlike déjà vu,
that seems to be a memory problem,
that these delusions are more related
to abnormal facial processing called visual agnosia.
But in the end, they are delusional disorders.
And I talk more about delusional disorder
and how it behaves in this video.
You can take a look to get more information.
See you next time.