March 4, 2026 • 35 mins
What happens to the things we remember when we can't remember them anymore? Jorge talks to two psychologists about the science of forgetting and the fascinating world of amnesia.
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Speaker 1 (00:00):
Hey, please take a second and leave us a review
on Apple Podcasts, Spotify, or wherever you listen to the podcast.
Thanks a lot. Hey, welcome to sign Stuff, a production
of iHeartRadio I'm More cham and today we're looking into amnesia.
How does it happen, why does it happen, and what
are some of the most dramatic cases of it in history.
(00:22):
It's part of a two part series on memory. So
if you haven't checked out the first episode about super memory,
go check it out. But in this episode, we're going
to explore what it means to edge and then erase
a memory. We're going to learn about a new technology
that can essentially suppress memories with the push of a button.
And we're going to look into amnesia and a condition
(00:43):
called severely deficient autobiographical memory, which once you hear about it,
you won't be able to forget. So tie a stringer
on your finger because we are going down a memory
hole to explore the science of amnesia. Enjoy. Hey everyone,
(01:04):
Today we're continuing our exploration of memory. In the previous episode,
we talked about the ability to remember a lot of things,
and now we're going to focus on we'regetting for example,
have you ever wondered what happens to a memory once
you can't remember it anymore? Or why sometimes, usually in
the worst possible moment, you can't remember an important piece
(01:26):
of information like your friend's name when you're introducing them
at a party. And then going further, what's actually happening
in people with amnesia or people who can't make new memories.
Have you seen the movie Memento or remember the character
of Dori and finding Nemo. Well, that actually happens in
real people. What's it like to be them and how
(01:47):
are they still able to function? We're going to tackle
all of these questions, starting with how memories are made
and how they're forgotten to tell us about the search
for the basic mechanism of memory. Talk to doctor Sarah
ro bin, a professor and the co director of the
Cognition Agency and Intelligence Center at Purdue University. Well, thank you,
(02:08):
doctor Robbins for joining us.
Speaker 2 (02:10):
Yes, thank you for having me. I am Sarah Robbins.
I'm a philosopher and cognitive scientist of memory. So I
study and in particular the science of memory.
Speaker 1 (02:19):
That's good that you remember all that I.
Speaker 2 (02:22):
No longer have to write it down takes a little bit.
Speaker 1 (02:26):
So that's an interesting mix between psychology and philosophy. Can
you tell us a little bit about that area in between.
Speaker 2 (02:33):
Yeah, and it includes neuroscience very deeply as well, So
I think of it as sort of different ways of
researching and thinking about the mind and the brain. Historically
they were very intertwined, so early psychology was often called
natural philosophy, and I often see the philosopher's role as
someone who's paying attention to what every one of those
(02:54):
is doing and talking about the bigger questions that started
the science in the first place.
Speaker 1 (02:58):
Feels a little like inceptions. It's like your researching what
we think of, how we think about, what we're learning about,
how we.
Speaker 2 (03:03):
Think, yes, exactly, that's fun.
Speaker 1 (03:08):
Okay. According to doctor Robins, scientists have been trying to
figure out how the brain records memories for a long time.
It's been a search for what scientists call the n gram.
Speaker 2 (03:19):
So an ingram is really the neural mechanism that makes
remember impossible or by which memories are supported so that
they can later be remembered.
Speaker 1 (03:29):
Okay, like how the brain stores information? Yeah, and I
guess for a long time people have been wondering like,
how does that work in the brain?
Speaker 2 (03:37):
Exactly? Yeah, how is it? Where is it? Like what
could possibly be the case? So the zoologists that coined
the term, Richard Demmon, she first wrote the book where
he coined the term in nineteen oh four in German.
He's calling it like it's somewhere in the irritable substance,
which is how people thought about the kind of material
of the brain at the time, which I just disagree.
Speaker 1 (03:59):
That's well, unfortunately I have a lot of irritable substance
in my brain we all, especially in the mornings.
Speaker 3 (04:06):
Yes, it's especially irritable.
Speaker 2 (04:08):
Then, absolutely there.
Speaker 1 (04:11):
So we've been looking for how the brain stores memories
for over a hundred years now. You might think, why
has it taken so long? Can we just open up
a brain and see what's going on? Well, it's not
that easy.
Speaker 2 (04:27):
One is a challenge that is, like it's hard to
know what's in your memory outside of actually like being
able to look in there. Right, So if you can't
remember something, it's kind of a question of like is
it in there but you can't get it out?
Speaker 3 (04:38):
Or is it not in there?
Speaker 2 (04:40):
But like how do you tell Like how do we
know what's really in there until we get it out.
Speaker 1 (04:46):
Yeah, it just made me realize what a difficult problem
this is because I think we're all familiar with memories.
We all have memories, we all remember things, but like,
how do you do an experiment on to figure out
how it works inside a brain as it's happening.
Speaker 2 (05:00):
Absolutely, And I think that's why some of these memories,
like when they come to you kind of out of nowhere,
are so delightful. Like when you hear a song you
haven't heard for twenty years and you remember all the word.
You can have this kind of like oh my gosh
sort of reaction to that. Oh it was in there,
and you sort of had no idea that it was there. Right,
It's not like I can like, oh, what other fun
stuff isn't there? Like I'm not going to know until
(05:22):
that happens again.
Speaker 1 (05:24):
Yeah, that is so tricky. In other words, it's hard
to study how the brain stores memories because you can't
just poke around someone's brain while they're making a memory
or trying to remember something. But all of that changed
about ten to fifteen years ago with the development of
a technology called optogenetics. I'll explain what that technology is
(05:46):
a little later. But first, here's what we've learned after
a century of science, but how the brain records a memory.
So you wrote in a paper that we found the nngram.
What does that mean that we've found it?
Speaker 2 (06:00):
I think it's now the case that it's possible to
identify the set of neurons that are active in storing memories.
Speaker 1 (06:06):
We'll step me through this. So I am walking around
and something incredible happens. The unicorn jumps out of the
manhole and then grows wings and flies off into the sky.
I'm definitely going to remember that. What's happening in my brain?
Speaker 3 (06:20):
Yes, So what's happening?
Speaker 1 (06:23):
I mean, I'll give you a second to process that image.
I just.
Speaker 2 (06:27):
Well, the unicorn area of processing and the manual air
and not there yet. So there's a set of cells
in the hippocampus and surrounding structures that are kind of
responsible for being the ones that react to that experience
and kind of encode information about that experience in somewhay,
there's a whole lot of neurons in that area, and
a subset of them are going to say, like we've
got this one here. You know, we're going to take
(06:48):
hold of that and something about the way that they
activate together capture something about that events.
Speaker 1 (06:54):
All right, So I see the unicorn. There are some
cells among the many, many, many many in my hippocampus
that are like I'm ready, I'm ready to remember things.
And then I see the unicorn. And it's what happens
to those cells. They sort of like change, they something
what happens.
Speaker 2 (07:11):
So they like become better connected to each other. I'm
not sure how far I can go with this metaphor,
but this is just like a sea of willing people
to play on the team for whatever sport you have.
Each time there's an experience, you like send a team
out and like they play together and they kind of
form a bond that makes them a team that is
about the experience.
Speaker 1 (07:32):
They lock hands, they're like, we got this memory. We're
going to remember that unicorn. We are the unicorn in
your head.
Speaker 2 (07:38):
We got it exactly. And then they kind of go
back into the sea and you bring out a new
set to play the next game and they do their connecting.
Speaker 1 (07:45):
So that, in a nutshell, is what we know about
how the brain records a memory, or at least a
memory of an event. There's an area in your brain
called the hippocampus, which sort of looks like two small
jalapeno peppers buried deep inside your with millions of neurons
in it, all connected to each other. And when something
memorable happens, some of those neurons, maybe a few hundred
(08:08):
of them, kind of get activated and they step up
to remember the event, and they do it by strengthening
the connections between them, which are called synopsis. The synopsis
get stronger, which means that network of cells is more
likely to activate together. As doctor Robin said, a good
analogy is to imagine a stadium full of people, and
(08:30):
when a new memory has to be recorded, as subset
of those people step up and they lock hands and
somehow that stores the memory. Okay, two quick things about that. First,
a neuron can be a part of multiple memories, not
just one.
Speaker 2 (08:46):
And it's possible over time that some of these cells
will play on different teams.
Speaker 1 (08:51):
Right, It's like I'm the unicorn cell with these group
of cells, but with these group of cells, I am
the I am the purple crocodile, or is another.
Speaker 3 (09:01):
Day exactly exactly And.
Speaker 1 (09:04):
Two that's what we see happening in the hippocampus during
an event, but we don't actually know if that's where
the memory is stored. Is a hippocampus kind of like
the hard drive of the brain, or is it more
like the relay of the brain, or like what's happening?
Speaker 3 (09:19):
I think that's a question of live debate.
Speaker 2 (09:21):
So it could be that it's individually storing each memory
and holding them and they stay in the hippocampus long term.
That is a view that some people hold. It could
be that it is just kind of a relay, like
it's the place that keeps tags or recipes, right, but
all the content is distributed elsewhere.
Speaker 1 (09:38):
Okay, that's what we know about how memories are formed.
Now the question is how do memories get forgotten and
what's happening in people with amnesia. We'll get to that,
but first I wanted to dig deeper into how we
know this is how memories are formed, because the answer
is pretty cool. It involves a fairly recent technology called optogenetics,
(10:01):
which basically lets you control memories with the push of
a button.
Speaker 2 (10:07):
And so that's changed in the last few decades thanks
to a range of sort of technological tool innovations. A
central one of which is something called optogenetics, which is
a technique for making neurons responsive to light. So, colloquially speaking,
you're putting a light switch on neurons. You make it
so that you can turn them on and off in
(10:29):
a living, behaving organism. So you can make certain neurons
fire action potentials, make them active, or you can inhibit
them keep them from firing action potentials. Wow, it's incredible.
Speaker 1 (10:44):
Okay, we can probably spend the whole episode just on
this technology because it's pretty wild. Basically, scientists can now
hack into the DNA of neurons and make it so
that when the neurons are activated, they produce a protein
that makes the neurons sensitive to light, and scientists can
time when this happens so that it only happens to
(11:05):
neurons in a specific brain area and during a specific event. So,
for example, you could make it so that everything you
experience in the next hour or so gets etched into
neurons in your hippocampus, and any neurons that get recruited
to remember those memories become light sensitive to you. Nothing
would change, You would simply have that memory as you
(11:27):
normally would. But now if I take a tiny fiber
optic flashlight and I thread it into your brain and
turn the light on. Those neurons that recorded that memory
would turn on and you would suddenly and involuntarily get
a flashback of what happened. And if you press the
button again, those neurons would activate again and you would
(11:49):
get a flashback again. Essentially, you could relive that memory
by just pressing that bun and scientists can also do
the reverse, which is to make to produced proteins that
make them stop working when they sense light. So you
could do the opposite, which is to make a memory
and then suppress that memory by simply turning on the light.
(12:12):
The scientists could make you forget something you just saw
by simply pushing on a button. It's pretty wild stuff,
and it involves things like immediate early genes and special
antibiotics to suppress these genes, which we don't have time
to cover this, but this is essentially what has unlocked
a lot of the memory research in the last ten years.
(12:34):
I didn't know we were that advance in this kind
of manipulation of neural activity.
Speaker 2 (12:39):
It's absolutely incredible to see what sorts of work could
be done in this way. And there are people that
have been using these similar techniques to sort of figure
out which neurons are trying to be a part of
the memory, and you can kind of follow them around
and again find the ngram in this way and then
activate and manipulate it.
Speaker 1 (12:55):
Okay, that is how we make memories. When we come back,
we'll get to the ession of how we forget memories
and what's happening in the brain of people with amnesia
and something called severely deficient autobiographical memory. We'll get to
all of that, So don't blink out. Lock in this memory.
We'll be right back. Hey, welcome back. We're talking about
(13:29):
the size of amnesia, and so far we've talked about
how the brain makes memories. Now we're going to talk
about how the brain forgets memories. As it turns out,
there's a big mystery about how we actually forget that
scientists haven't figured it out. To take us through this,
here's doctor DANIELA. Palombo, Professor of psychology at the University
(13:49):
of British Columbia. Well, thank you doctor Palombo for joining
us again.
Speaker 3 (13:54):
Yeah, my pleasure.
Speaker 1 (13:55):
So I thought it'd be interesting to talk about the
absence of memories what are some of the different ways
that we can lose memories.
Speaker 4 (14:02):
Yeah, that's a really good question. So I guess I'll
start by saying that any of us can lose our memories.
Speaker 1 (14:09):
Okay. According to doctor Palombo, there are several kinds of
memory loss. First is the casual kind that we all
experience every day in our memory slips.
Speaker 4 (14:20):
So in our day to day lives, you know, whether
we're young or older, we see that we experience memory
slips where we think we should have access to something
we don't, and that happens to all of us all
the time. I'm sure you've experienced this many times. And
so I have a very vivid memory of a time
where I was introducing a bunch of people at a
party and I had a coworker over who I knew
(14:43):
very well, and I just temporarily forgot my coworkers seeing
and he was staring at me in shock and disbelief,
and I was also very very surprised and embarrassed, and
then you know, a few minutes later, it popped back
into my mind. So that type of loss refers to
temporary and access to information, and it certainly happens as
(15:06):
we get older and This is all part of healthy aging.
Speaker 1 (15:09):
I see, are you still friends with this person or
that relationship?
Speaker 3 (15:14):
They did forgive me thanks leady.
Speaker 1 (15:16):
They forgot about it. Well, this makes the question about
in the situations where we can get at a memory,
but later on we remember, like what happens there? Like
where does that memory go that I can't excess it?
Speaker 4 (15:28):
So sometimes it's simply due to interference. So we're in
a situation where we're just not searching for the memory
in the right way, and then later on something in
our environment might trigger that memory. Sometimes it's because we're
feeling very stressed. It can be feeling a bit anxious
in the moment.
Speaker 1 (15:45):
So that's a memory slip where we have temporary trouble
accessing a memory. There's also just forgetting something over time.
Is there just plain forgetting? Like is it possible for
me to have stored a memory in my brain cells
but over time they just sort of, you know, like
the hard drive gets corrupted or erased.
Speaker 4 (16:07):
Yes, so forgetting is a pretty loaded term. But you're
right that we can form memories and then over time
those memories become difficult to access. And one hypothesis is
that that's because there's lots of interfering new information that
we're encoding and needing to retrieve, and so the more
memories we form over our lifetime, the more competition there is.
Speaker 2 (16:29):
Right.
Speaker 4 (16:29):
Another hypothesis is that just as our lives change and
we grow, et cetera, the retrieval cues that we use
to access those really old memories are not as close
to our fingertips anymore. So you've moved on from your
childhood home, et cetera, so it's harder to access those memories.
Speaker 1 (16:48):
I see, you sort of lose the path to those memories.
Speaker 3 (16:52):
Yeah, exactly.
Speaker 1 (16:54):
So some things you can lose a memory because you
lose a connection to it. It's still in your brain,
but because it's simply not relevant to you, you never
find your way to it again. Now, memory slips and
losing connections to your memories over time are both natural processes.
They happen to anyone. But now we get to the
kind of memory loss that's due to something specific.
Speaker 4 (17:17):
And that can happen in the context of disease. So
you've probably heard about different forms of dementia, like Alzheimer's disease,
where you can see quite profound, albeit progressive memory loss.
And then there's another condition called amnesia. Then this is
often due to a brain injury of virus. It can
(17:38):
happen in the context of a stroke, and here.
Speaker 1 (17:41):
We get to amnesia. Now, the thing about amnesia is
that it typically happens because of an event. It could
be a stroke or a traumatic brain injury, or sometimes
it's a virus that infects your brain. Whatever the cause,
most cases of amnesia have something in common.
Speaker 4 (17:59):
Yeah, lots of different causes to amnesia, but one thing
that they have in common is that they affect really
similar networks in the brain. And there's one area of
the brain in particular that's quite vulnerable to whether it's
a virus or certain kinds of stroke, certain kinds of
traumatic brain injury, et cetera, epilepsy, and that's a region
of the brain called the hippocampus. And so when that
(18:22):
area of the brain is affected, regardless of the cause,
you see a profound loss of memory.
Speaker 1 (18:30):
Yes, the thing most cases when anesia have in common
is that they affect the hippok campus. Now, once the
hippocampus's damaged, two basic things can happen. One, you can
lose past memories that you had before the event the
damage to hippocampus. For example, childhood memories, the names of people,
those could all be gone. And two, you can also
(18:53):
lose the ability to make new memories after the event,
and both of these kinds of anesia have different names.
Using memories you had before the event is called retrograde anesia,
and losing the ability to make new memories is called
terograde anesia. You're probably familiar with these kinds of anesia
(19:14):
just from popular culture. In a soap opera, when someone
has an accident and they can't remember who they are
or anything about their history, that's retrograde anesia. And in
the movie Memento or with Dory and Finding Nemo, where
the character seems to forget everything that happens to them
and everything seems new to them, that's anterograde anesia. Now,
(19:36):
there are a couple of fascinating things to talk about
in each of these kinds of anesia. We'll start with
retrograde anesia, where you lose your past memories. The fascinating
thing is that scientists aren't really sure if you actually
lose your memories.
Speaker 4 (19:52):
Yeah, so this is a question that a lot of
memory scientists have what does it actually mean to have
loss of memory? And so the one hypothesis is that
the places in the brain where the memories are stored
are damaged and so those memories are gone. And another
hypothesis that you're getting at is that the memories are
still stored somewhere in the brain, but via damage to
(20:15):
the hippocampus, those memories cannot be accessed.
Speaker 1 (20:18):
Wow, So the memories are still.
Speaker 4 (20:19):
In there potentially potentially Yeah, Because remember last time we spoke,
I sort of described this idea that the hippocampus in
particular is a pointer to different parts of the brain
where the memories are kind of stored within a network,
and so when that index pointer is not working anymore,
those memories are not accessible. Now we don't know for sure,
(20:40):
because there's a lot about memory and the brain that
we don't yet understand, but that is one idea that's
been put out there.
Speaker 1 (20:47):
Yes, if you have retrograde amnesia, your memories might still
be intact in your brain and what you lose is
actually the ability to access them, although that doesn't mean
you could get them back.
Speaker 4 (21:00):
Some cases, like in soap operas for example, sometimes it
does involve an injury to the head, and so you'll
see a situation where somebody got bonked on the head.
They can't remember anything, including who they are, for a
period of time, and then oftentimes they get bonked on
the head again and that sort of shakes them out
of the amnesic syndrome. And so that's not an accurate
(21:22):
depiction of what looks like.
Speaker 1 (21:24):
Oh no. Now, for people with anterograde amnesia, or the
inability to make new memories, there are two fascinating things
about them. The first is that because they can't make
new episodic memories, they live in a constant state of surprise,
as if they are just waking up every so often,
because anything that's happened to them recently they don't remember.
Speaker 4 (21:48):
What we tend to see is this kind of profound
loss of episodic memory. And that's kind of the most
striking feature of amnesia. And what I mean by that
is if you're sitting with an m music participant and
you're having a conversation and you leave the room for
a few minutes and you return, they're not necessarily going
to remember that conversation. They're not going to remember that
you met them, what you talked about, et cetera, and
(22:11):
they also have difficulty remembering new facts, even though they
actually can access semantic memories from before their injury, so
they know who they are, they know lots about the world,
et cetera.
Speaker 1 (22:24):
One of the most extreme examples of this kind of
amnesia is a man named Clive Wearing. He's still alive today.
He's eighty seven years old now, but when he was
forty seven, a virus got into his brain and destroyed
a lot of his hip hook campus. This prevents him
from remembering anything that happens beyond about seven seconds. So
(22:47):
you can have a conversation with him, but after a
short while, he won't remember who you are, what you
were talking about, or even how he got to the
place where he is right now now. Before the virus,
mister Wearing was a musicologist and an orchestra conductor, so
he still remembers how to play music, and he also
remembers his wife and the fact that he has kids,
(23:08):
but he only remembers his kids from when they were little.
Try to imagine what it would be like to be yourself,
but to find yourself in a constant state of not
knowing where you are or how anything around you got
to where it was we're not being able to recognize
any of the people around you, even though they act
perfectly normal, as if they've been hanging out with you
(23:28):
for a while. It's pretty mind boggling. But here's the
other fascinating thing about people with anteror grade amnesia. They
can often still learn new skills. We'll get to what
that means and how we know that after the break.
Stay with us, we'll be right back. Hey, welcome back.
(24:02):
We're talking about the science of forgetting, and so far
we talked about anesia and the different kinds of it.
There's a kind where you don't remember memories you had
before the injury that caused the amnesia. That's called retrograde amnesia.
And there's a kind where you can't make new memories
starting from the time of the injury. That's called anterograde amnesia.
(24:23):
And we also talked about several fascinating things about each
of these kinds. Now, another fascinating thing about anterograde amnesia,
where someone can't make new episodic memories like in the
movie Memento or Dory from Finding Nemo, came from one
of the first cases of this kind of anesia ever studied,
which was a man named Henry Mollison. Henry Mollison, Yeah,
(24:45):
the famous patient HM.
Speaker 4 (24:47):
Yes, exactly. So he was studied for many decades and
this first began in the nineteen fifties. So he had
a surgery in nineteen fifty three to remove parts of
the brain that are really important for memory, such as
the hippocampus as well as the surrounding medial tempor lobe structures,
and all of that was removed in HM in this
(25:09):
surgery to help relieve intractable epilepsies. So after HM surgery,
at first blush, it appeared that the removal of this
tissue had kind of little impact on his cognition, but
it soon became clear that his memory was sort of
somewhat selectively and deeply affected.
Speaker 3 (25:29):
He was profound me in music.
Speaker 1 (25:31):
So Henry Mullison had severe and terror grade amnesia, just
like dor and finding Nemo or Clive Wearing the music
conductor I talked about before, if you met Henry, he
would forget about you within a few minutes of meeting you,
which meant he lived in a constant state of not
knowing where he was or how he got there, But scientists,
namely a researcher called Brenda Milner, soon figured out something amazing.
(25:56):
Henry could learn new skills.
Speaker 4 (26:00):
Come into the laboratory, and he'd be given a new
skill task, but he wouldn't remember ever having been exposed
to the task. He'd come in day after day and
he would perform it as though it was a brand
new task for him, even though he was getting better
over time.
Speaker 1 (26:14):
So scientists learned they could teach Henry new skills, but
he wouldn't remember having learned those skills. For example, you
could teach him to play the piano or to play tennis,
and he wouldn't remember taking the lessons, But the next
time he would sit in front of a piano or
pick up a tennis racket, he'd be amazed that he
knew how to use them. And this is because, as
(26:34):
we talked about before, there are different kinds of memory
in your brain. Remembering things that happened to you, or
the fact that you took music or tennis lessons are explicit,
episodic or semantic memories, but knowing how to hit the
keys on a piano or how to swing a tennis
racket are implicit motor memories. This case of Henry Mullyson
(26:55):
unlocked a lot of what we now know about the
different memory systems in our brain. Now, I talked about
the two basic kinds of anesia, losing old memories and
not being able to form new memories, as if there
are different kinds of anesia, and they are, but according
to doctor Palombo, they often happened together. Patient HM Henry
Mollison had both, as well as Clive Wearing and Dori
(27:19):
in finding Nemo. Okay, we're now going to get to
the last kind of forgetting, which is a condition called
severely deficient autobiographical memory. According to doctor Palombo, this is
similar to interrograde anesia, except it's a condition that some
people seem to be born with.
Speaker 4 (27:39):
So I did some work on what we refer to
as severely deficient autobiographical memory. And my work on STAM
was done in collaboration with doctor Brian Levine, and we
studied a group of three individuals who contacted us and
shared with us that they had profound difficulty or even
(27:59):
an inability to vividly recollect events from their past wow,
but were otherwise healthy and high functioning. And so we
brought these individuals into our lab and we studied them
for a few years, and we studied the way that
they remember episodes to you know, try to see what
we can sort of understand about memory from studying these
(28:22):
individuals who fall at the kind of other end of
the extreme to that of age SAM, who are as
we remember, people who remember quite a lot.
Speaker 1 (28:31):
Okay, if you remember, in our last episode about super memory,
we talked about people with something called highly superior autobiographical
memory or h SAM, who could remember everything that's ever
happened to them in their lives. Well, people with severely
deficient autobiographical memory or as DAM, are sort of the
opposite of that condition. They can't remember anything that happens
(28:55):
to them.
Speaker 4 (28:57):
And so I'll say early days with us as it
is with h SAM, And so our scientific understanding of
SDAM is quite limited. But what we do know so
far is that it seems like individuals with SDAM access
their past in a different way. And so rather than
reliving episodes from their past in vivid and rich detail,
(29:18):
they tend to access their past more through semantic remembering.
Speaker 1 (29:22):
I see it. Could you describe the condition, like what
is it like for them?
Speaker 4 (29:26):
So it kind of depends on the person, and so
some people will describe having difficulty accessing visual images through
their memory. And so it's mainly that this sort of
conscious access to reexperiencing the past is limited or absent.
But yet nonetheless they can access their knowledge about the
(29:47):
world and through facts. And so oftentimes you'll hear individuals
with SDAMS say that they just know their past, but
they're not reliving it in that sort of rich episodic format.
Speaker 1 (30:00):
Like I remember I went to college at the University
of Toronto, but I have no memories of being there
or what it was like exactly.
Speaker 4 (30:08):
Yes, the episodes that can be relived.
Speaker 1 (30:13):
Yes, there are people out there that can remember facts
about their lives, but they don't actually remember living it.
They don't seem to be able to record the kind
of memory that lets you relive your past. They know
they were there, but they don't remember being there. Uh.
It's like I know I had a kid, and I
(30:35):
know they were really young, but I have no memories
of those early days taking care of newbore.
Speaker 3 (30:39):
Yes, exactly.
Speaker 4 (30:40):
And so you have lots of information about your lives,
about your loved ones, et cetera, but it's just you're
not accessing that information through episodic memory.
Speaker 1 (30:49):
Uh, like my record button just wasn't on.
Speaker 4 (30:52):
Possibly it could be that the record button was on,
but it's a different pathway towards accessing those memories. So
that could be right from the get go, that memories
are being laid down in a more factual conceptual way.
That's a very open question.
Speaker 1 (31:08):
Oh, I see they might have the record but on,
but maybe the camera works a little bit different.
Speaker 3 (31:14):
That's right exactly.
Speaker 1 (31:15):
I see, what do you think and this might not
be a scientific question, but what is it like too?
Speaker 4 (31:23):
Yeah, so I think you're asking a little bit about
sort of what the lived experience of ASBM is.
Speaker 1 (31:30):
Yeah.
Speaker 4 (31:30):
I think that's such an important question. And I think
as scientists sometimes we get wrapped up in studying the
nuts and bolts of what memory might look like in
a particular group of individuals, and I think it's important
to take a step back and think about what those
lived experiences are like for our participants. Anecdotally, I guess
I'll say that for some individuals, lacking this re experiencing
(31:53):
component of memory can be hard for them and for
others less so. And so I think in the individuals
we studied, they were high functioning in terms of their
day to day and they were by all accounts healthy.
You know, I think that individuals with STAM feel in
the moment probably as richly and profoundly as the rest
of us do. But it could be that just the
(32:15):
way that one reflects on their past, that there's individual
differences there. So it could be that when you don't
have access to the past in terms of re experiencing episodes,
it might help you move on from the past when
things were difficult.
Speaker 1 (32:30):
This brings us to the last question I had for
doctor Palumbo, which is, why do we forget in the
first place. If it's possible to remember everything that happens
to you in your life, as some people would super
memory prove, why didn't we all evolve disability to remember everything?
What's the point of forgetting?
Speaker 4 (32:53):
Yes, exactly. And that might seem strange because we would
hope that our memory systems would be a perfect record
the past. That would be really helpful in many situations.
But in fact, memory researchers would argue that it is
actually adaptive to forget, and we sort of have this
sweet spot of remembering just enough so we live. We
(33:17):
are encoding experiences at every moment, and a lot of
things repeat in our environment, so we're picking up patterns
in the world, and it's that kind of information that's
really useful to us when we're thinking about decisions we
need to make in the moment or planning out our future,
et cetera. So we actually think that having an imperfect
(33:37):
memory system, a memory system that's flexible and reconstructive, is
actually really good for us.
Speaker 1 (33:43):
Yeah, I guess the idea is that your memory is
meant to be a little fuzzy so that you can
see the larger patterns in your life.
Speaker 3 (33:52):
Yeah, that's a really good way to put it.
Speaker 1 (33:54):
So you don't miss the forest for the trees.
Speaker 4 (33:57):
Kind yes, exactly exactly, because we all didn't have to
make really quick decisions, especially if we're being threatened by something,
and so we want to know how things generally occur,
not necessarily how they occurred just once.
Speaker 1 (34:11):
I see, like, we don't get hung up on whether
the tiger running at you have the same stripes as
the last tiger you saw a few weeks ago. You
just want to remember it it's a tiger. At least
you run away.
Speaker 3 (34:22):
That's exactly right.
Speaker 1 (34:23):
Yes, oh interesting, So there's a reason I'm forget that.
What we're saying, there's there's a good reason, very.
Speaker 3 (34:29):
Good reason you're forgetful.
Speaker 1 (34:30):
Yeah, yeah, all right. That was a lot of information
about memory, amnesia and forgetting. But the good news is
that if you don't exactly remember the things we talked about,
you can just get the replay button and you'll get
to relive these conversations all over again. It's like our
phones and our computers are now part of our extended memory.
(34:53):
Thanks for joining us, don't forget to come back next week.
See then you've been listening to science Stuff. The production
of iHeartRadio written and produced by me Or Hitcham, edited
by Rose Seguda, executive producer Jerry Rowland, and audio engineer
and mixer Kasey Pegram. And you can follow me on
(35:15):
social media. Just search for PhD Comics and the name
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Stuff on the iHeartRadio app, Apple Podcasts, or wherever you
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back next Wednesday with another episode.
Hey, please take a second and leave us a review
on Apple Podcasts, Spotify, or wherever you listen to the podcast.
Thanks a lot. Hey, welcome to sign Stuff, a production
of iHeartRadio I'm More cham and today we're looking into amnesia.
How does it happen, why does it happen, and what
are some of the most dramatic cases of it in history.
(00:22):
It's part of a two part series on memory. So
if you haven't checked out the first episode about super memory,
go check it out. But in this episode, we're going
to explore what it means to edge and then erase
a memory. We're going to learn about a new technology
that can essentially suppress memories with the push of a button.
And we're going to look into amnesia and a condition
(00:43):
called severely deficient autobiographical memory, which once you hear about it,
you won't be able to forget. So tie a stringer
on your finger because we are going down a memory
hole to explore the science of amnesia. Enjoy. Hey everyone,
(01:04):
Today we're continuing our exploration of memory. In the previous episode,
we talked about the ability to remember a lot of things,
and now we're going to focus on we'regetting for example,
have you ever wondered what happens to a memory once
you can't remember it anymore? Or why sometimes, usually in
the worst possible moment, you can't remember an important piece
(01:26):
of information like your friend's name when you're introducing them
at a party. And then going further, what's actually happening
in people with amnesia or people who can't make new memories.
Have you seen the movie Memento or remember the character
of Dori and finding Nemo. Well, that actually happens in
real people. What's it like to be them and how
(01:47):
are they still able to function? We're going to tackle
all of these questions, starting with how memories are made
and how they're forgotten to tell us about the search
for the basic mechanism of memory. Talk to doctor Sarah
ro bin, a professor and the co director of the
Cognition Agency and Intelligence Center at Purdue University. Well, thank you,
(02:08):
doctor Robbins for joining us.
Speaker 2 (02:10):
Yes, thank you for having me. I am Sarah Robbins.
I'm a philosopher and cognitive scientist of memory. So I
study and in particular the science of memory.
Speaker 1 (02:19):
That's good that you remember all that I.
Speaker 2 (02:22):
No longer have to write it down takes a little bit.
Speaker 1 (02:26):
So that's an interesting mix between psychology and philosophy. Can
you tell us a little bit about that area in between.
Speaker 2 (02:33):
Yeah, and it includes neuroscience very deeply as well, So
I think of it as sort of different ways of
researching and thinking about the mind and the brain. Historically
they were very intertwined, so early psychology was often called
natural philosophy, and I often see the philosopher's role as
someone who's paying attention to what every one of those
(02:54):
is doing and talking about the bigger questions that started
the science in the first place.
Speaker 1 (02:58):
Feels a little like inceptions. It's like your researching what
we think of, how we think about, what we're learning about,
how we.
Speaker 2 (03:03):
Think, yes, exactly, that's fun.
Speaker 1 (03:08):
Okay. According to doctor Robins, scientists have been trying to
figure out how the brain records memories for a long time.
It's been a search for what scientists call the n gram.
Speaker 2 (03:19):
So an ingram is really the neural mechanism that makes
remember impossible or by which memories are supported so that
they can later be remembered.
Speaker 1 (03:29):
Okay, like how the brain stores information? Yeah, and I
guess for a long time people have been wondering like,
how does that work in the brain?
Speaker 2 (03:37):
Exactly? Yeah, how is it? Where is it? Like what
could possibly be the case? So the zoologists that coined
the term, Richard Demmon, she first wrote the book where
he coined the term in nineteen oh four in German.
He's calling it like it's somewhere in the irritable substance,
which is how people thought about the kind of material
of the brain at the time, which I just disagree.
Speaker 1 (03:59):
That's well, unfortunately I have a lot of irritable substance
in my brain we all, especially in the mornings.
Speaker 3 (04:06):
Yes, it's especially irritable.
Speaker 2 (04:08):
Then, absolutely there.
Speaker 1 (04:11):
So we've been looking for how the brain stores memories
for over a hundred years now. You might think, why
has it taken so long? Can we just open up
a brain and see what's going on? Well, it's not
that easy.
Speaker 2 (04:27):
One is a challenge that is, like it's hard to
know what's in your memory outside of actually like being
able to look in there. Right, So if you can't
remember something, it's kind of a question of like is
it in there but you can't get it out?
Speaker 3 (04:38):
Or is it not in there?
Speaker 2 (04:40):
But like how do you tell Like how do we
know what's really in there until we get it out.
Speaker 1 (04:46):
Yeah, it just made me realize what a difficult problem
this is because I think we're all familiar with memories.
We all have memories, we all remember things, but like,
how do you do an experiment on to figure out
how it works inside a brain as it's happening.
Speaker 2 (05:00):
Absolutely, And I think that's why some of these memories,
like when they come to you kind of out of nowhere,
are so delightful. Like when you hear a song you
haven't heard for twenty years and you remember all the word.
You can have this kind of like oh my gosh
sort of reaction to that. Oh it was in there,
and you sort of had no idea that it was there. Right,
It's not like I can like, oh, what other fun
stuff isn't there? Like I'm not going to know until
(05:22):
that happens again.
Speaker 1 (05:24):
Yeah, that is so tricky. In other words, it's hard
to study how the brain stores memories because you can't
just poke around someone's brain while they're making a memory
or trying to remember something. But all of that changed
about ten to fifteen years ago with the development of
a technology called optogenetics. I'll explain what that technology is
(05:46):
a little later. But first, here's what we've learned after
a century of science, but how the brain records a memory.
So you wrote in a paper that we found the nngram.
What does that mean that we've found it?
Speaker 2 (06:00):
I think it's now the case that it's possible to
identify the set of neurons that are active in storing memories.
Speaker 1 (06:06):
We'll step me through this. So I am walking around
and something incredible happens. The unicorn jumps out of the
manhole and then grows wings and flies off into the sky.
I'm definitely going to remember that. What's happening in my brain?
Speaker 3 (06:20):
Yes, So what's happening?
Speaker 1 (06:23):
I mean, I'll give you a second to process that image.
I just.
Speaker 2 (06:27):
Well, the unicorn area of processing and the manual air
and not there yet. So there's a set of cells
in the hippocampus and surrounding structures that are kind of
responsible for being the ones that react to that experience
and kind of encode information about that experience in somewhay,
there's a whole lot of neurons in that area, and
a subset of them are going to say, like we've
got this one here. You know, we're going to take
(06:48):
hold of that and something about the way that they
activate together capture something about that events.
Speaker 1 (06:54):
All right, So I see the unicorn. There are some
cells among the many, many, many many in my hippocampus
that are like I'm ready, I'm ready to remember things.
And then I see the unicorn. And it's what happens
to those cells. They sort of like change, they something
what happens.
Speaker 2 (07:11):
So they like become better connected to each other. I'm
not sure how far I can go with this metaphor,
but this is just like a sea of willing people
to play on the team for whatever sport you have.
Each time there's an experience, you like send a team
out and like they play together and they kind of
form a bond that makes them a team that is
about the experience.
Speaker 1 (07:32):
They lock hands, they're like, we got this memory. We're
going to remember that unicorn. We are the unicorn in
your head.
Speaker 2 (07:38):
We got it exactly. And then they kind of go
back into the sea and you bring out a new
set to play the next game and they do their connecting.
Speaker 1 (07:45):
So that, in a nutshell, is what we know about
how the brain records a memory, or at least a
memory of an event. There's an area in your brain
called the hippocampus, which sort of looks like two small
jalapeno peppers buried deep inside your with millions of neurons
in it, all connected to each other. And when something
memorable happens, some of those neurons, maybe a few hundred
(08:08):
of them, kind of get activated and they step up
to remember the event, and they do it by strengthening
the connections between them, which are called synopsis. The synopsis
get stronger, which means that network of cells is more
likely to activate together. As doctor Robin said, a good
analogy is to imagine a stadium full of people, and
(08:30):
when a new memory has to be recorded, as subset
of those people step up and they lock hands and
somehow that stores the memory. Okay, two quick things about that. First,
a neuron can be a part of multiple memories, not
just one.
Speaker 2 (08:46):
And it's possible over time that some of these cells
will play on different teams.
Speaker 1 (08:51):
Right, It's like I'm the unicorn cell with these group
of cells, but with these group of cells, I am
the I am the purple crocodile, or is another.
Speaker 3 (09:01):
Day exactly exactly And.
Speaker 1 (09:04):
Two that's what we see happening in the hippocampus during
an event, but we don't actually know if that's where
the memory is stored. Is a hippocampus kind of like
the hard drive of the brain, or is it more
like the relay of the brain, or like what's happening?
Speaker 3 (09:19):
I think that's a question of live debate.
Speaker 2 (09:21):
So it could be that it's individually storing each memory
and holding them and they stay in the hippocampus long term.
That is a view that some people hold. It could
be that it is just kind of a relay, like
it's the place that keeps tags or recipes, right, but
all the content is distributed elsewhere.
Speaker 1 (09:38):
Okay, that's what we know about how memories are formed.
Now the question is how do memories get forgotten and
what's happening in people with amnesia. We'll get to that,
but first I wanted to dig deeper into how we
know this is how memories are formed, because the answer
is pretty cool. It involves a fairly recent technology called optogenetics,
(10:01):
which basically lets you control memories with the push of
a button.
Speaker 2 (10:07):
And so that's changed in the last few decades thanks
to a range of sort of technological tool innovations. A
central one of which is something called optogenetics, which is
a technique for making neurons responsive to light. So, colloquially speaking,
you're putting a light switch on neurons. You make it
so that you can turn them on and off in
(10:29):
a living, behaving organism. So you can make certain neurons
fire action potentials, make them active, or you can inhibit
them keep them from firing action potentials. Wow, it's incredible.
Speaker 1 (10:44):
Okay, we can probably spend the whole episode just on
this technology because it's pretty wild. Basically, scientists can now
hack into the DNA of neurons and make it so
that when the neurons are activated, they produce a protein
that makes the neurons sensitive to light, and scientists can
time when this happens so that it only happens to
(11:05):
neurons in a specific brain area and during a specific event. So,
for example, you could make it so that everything you
experience in the next hour or so gets etched into
neurons in your hippocampus, and any neurons that get recruited
to remember those memories become light sensitive to you. Nothing
would change, You would simply have that memory as you
(11:27):
normally would. But now if I take a tiny fiber
optic flashlight and I thread it into your brain and
turn the light on. Those neurons that recorded that memory
would turn on and you would suddenly and involuntarily get
a flashback of what happened. And if you press the
button again, those neurons would activate again and you would
(11:49):
get a flashback again. Essentially, you could relive that memory
by just pressing that bun and scientists can also do
the reverse, which is to make to produced proteins that
make them stop working when they sense light. So you
could do the opposite, which is to make a memory
and then suppress that memory by simply turning on the light.
(12:12):
The scientists could make you forget something you just saw
by simply pushing on a button. It's pretty wild stuff,
and it involves things like immediate early genes and special
antibiotics to suppress these genes, which we don't have time
to cover this, but this is essentially what has unlocked
a lot of the memory research in the last ten years.
(12:34):
I didn't know we were that advance in this kind
of manipulation of neural activity.
Speaker 2 (12:39):
It's absolutely incredible to see what sorts of work could
be done in this way. And there are people that
have been using these similar techniques to sort of figure
out which neurons are trying to be a part of
the memory, and you can kind of follow them around
and again find the ngram in this way and then
activate and manipulate it.
Speaker 1 (12:55):
Okay, that is how we make memories. When we come back,
we'll get to the ession of how we forget memories
and what's happening in the brain of people with amnesia
and something called severely deficient autobiographical memory. We'll get to
all of that, So don't blink out. Lock in this memory.
We'll be right back. Hey, welcome back. We're talking about
(13:29):
the size of amnesia, and so far we've talked about
how the brain makes memories. Now we're going to talk
about how the brain forgets memories. As it turns out,
there's a big mystery about how we actually forget that
scientists haven't figured it out. To take us through this,
here's doctor DANIELA. Palombo, Professor of psychology at the University
(13:49):
of British Columbia. Well, thank you doctor Palombo for joining
us again.
Speaker 3 (13:54):
Yeah, my pleasure.
Speaker 1 (13:55):
So I thought it'd be interesting to talk about the
absence of memories what are some of the different ways
that we can lose memories.
Speaker 4 (14:02):
Yeah, that's a really good question. So I guess I'll
start by saying that any of us can lose our memories.
Speaker 1 (14:09):
Okay. According to doctor Palombo, there are several kinds of
memory loss. First is the casual kind that we all
experience every day in our memory slips.
Speaker 4 (14:20):
So in our day to day lives, you know, whether
we're young or older, we see that we experience memory
slips where we think we should have access to something
we don't, and that happens to all of us all
the time. I'm sure you've experienced this many times. And
so I have a very vivid memory of a time
where I was introducing a bunch of people at a
party and I had a coworker over who I knew
(14:43):
very well, and I just temporarily forgot my coworkers seeing
and he was staring at me in shock and disbelief,
and I was also very very surprised and embarrassed, and
then you know, a few minutes later, it popped back
into my mind. So that type of loss refers to
temporary and access to information, and it certainly happens as
(15:06):
we get older and This is all part of healthy aging.
Speaker 1 (15:09):
I see, are you still friends with this person or
that relationship?
Speaker 3 (15:14):
They did forgive me thanks leady.
Speaker 1 (15:16):
They forgot about it. Well, this makes the question about
in the situations where we can get at a memory,
but later on we remember, like what happens there? Like
where does that memory go that I can't excess it?
Speaker 4 (15:28):
So sometimes it's simply due to interference. So we're in
a situation where we're just not searching for the memory
in the right way, and then later on something in
our environment might trigger that memory. Sometimes it's because we're
feeling very stressed. It can be feeling a bit anxious
in the moment.
Speaker 1 (15:45):
So that's a memory slip where we have temporary trouble
accessing a memory. There's also just forgetting something over time.
Is there just plain forgetting? Like is it possible for
me to have stored a memory in my brain cells
but over time they just sort of, you know, like
the hard drive gets corrupted or erased.
Speaker 4 (16:07):
Yes, so forgetting is a pretty loaded term. But you're
right that we can form memories and then over time
those memories become difficult to access. And one hypothesis is
that that's because there's lots of interfering new information that
we're encoding and needing to retrieve, and so the more
memories we form over our lifetime, the more competition there is.
Speaker 2 (16:29):
Right.
Speaker 4 (16:29):
Another hypothesis is that just as our lives change and
we grow, et cetera, the retrieval cues that we use
to access those really old memories are not as close
to our fingertips anymore. So you've moved on from your
childhood home, et cetera, so it's harder to access those memories.
Speaker 1 (16:48):
I see, you sort of lose the path to those memories.
Speaker 3 (16:52):
Yeah, exactly.
Speaker 1 (16:54):
So some things you can lose a memory because you
lose a connection to it. It's still in your brain,
but because it's simply not relevant to you, you never
find your way to it again. Now, memory slips and
losing connections to your memories over time are both natural processes.
They happen to anyone. But now we get to the
kind of memory loss that's due to something specific.
Speaker 4 (17:17):
And that can happen in the context of disease. So
you've probably heard about different forms of dementia, like Alzheimer's disease,
where you can see quite profound, albeit progressive memory loss.
And then there's another condition called amnesia. Then this is
often due to a brain injury of virus. It can
(17:38):
happen in the context of a stroke, and here.
Speaker 1 (17:41):
We get to amnesia. Now, the thing about amnesia is
that it typically happens because of an event. It could
be a stroke or a traumatic brain injury, or sometimes
it's a virus that infects your brain. Whatever the cause,
most cases of amnesia have something in common.
Speaker 4 (17:59):
Yeah, lots of different causes to amnesia, but one thing
that they have in common is that they affect really
similar networks in the brain. And there's one area of
the brain in particular that's quite vulnerable to whether it's
a virus or certain kinds of stroke, certain kinds of
traumatic brain injury, et cetera, epilepsy, and that's a region
of the brain called the hippocampus. And so when that
(18:22):
area of the brain is affected, regardless of the cause,
you see a profound loss of memory.
Speaker 1 (18:30):
Yes, the thing most cases when anesia have in common
is that they affect the hippok campus. Now, once the
hippocampus's damaged, two basic things can happen. One, you can
lose past memories that you had before the event the
damage to hippocampus. For example, childhood memories, the names of people,
those could all be gone. And two, you can also
(18:53):
lose the ability to make new memories after the event,
and both of these kinds of anesia have different names.
Using memories you had before the event is called retrograde anesia,
and losing the ability to make new memories is called
terograde anesia. You're probably familiar with these kinds of anesia
(19:14):
just from popular culture. In a soap opera, when someone
has an accident and they can't remember who they are
or anything about their history, that's retrograde anesia. And in
the movie Memento or with Dory and Finding Nemo, where
the character seems to forget everything that happens to them
and everything seems new to them, that's anterograde anesia. Now,
(19:36):
there are a couple of fascinating things to talk about
in each of these kinds of anesia. We'll start with
retrograde anesia, where you lose your past memories. The fascinating
thing is that scientists aren't really sure if you actually
lose your memories.
Speaker 4 (19:52):
Yeah, so this is a question that a lot of
memory scientists have what does it actually mean to have
loss of memory? And so the one hypothesis is that
the places in the brain where the memories are stored
are damaged and so those memories are gone. And another
hypothesis that you're getting at is that the memories are
still stored somewhere in the brain, but via damage to
(20:15):
the hippocampus, those memories cannot be accessed.
Speaker 1 (20:18):
Wow, So the memories are still.
Speaker 4 (20:19):
In there potentially potentially Yeah, Because remember last time we spoke,
I sort of described this idea that the hippocampus in
particular is a pointer to different parts of the brain
where the memories are kind of stored within a network,
and so when that index pointer is not working anymore,
those memories are not accessible. Now we don't know for sure,
(20:40):
because there's a lot about memory and the brain that
we don't yet understand, but that is one idea that's
been put out there.
Speaker 1 (20:47):
Yes, if you have retrograde amnesia, your memories might still
be intact in your brain and what you lose is
actually the ability to access them, although that doesn't mean
you could get them back.
Speaker 4 (21:00):
Some cases, like in soap operas for example, sometimes it
does involve an injury to the head, and so you'll
see a situation where somebody got bonked on the head.
They can't remember anything, including who they are, for a
period of time, and then oftentimes they get bonked on
the head again and that sort of shakes them out
of the amnesic syndrome. And so that's not an accurate
(21:22):
depiction of what looks like.
Speaker 1 (21:24):
Oh no. Now, for people with anterograde amnesia, or the
inability to make new memories, there are two fascinating things
about them. The first is that because they can't make
new episodic memories, they live in a constant state of surprise,
as if they are just waking up every so often,
because anything that's happened to them recently they don't remember.
Speaker 4 (21:48):
What we tend to see is this kind of profound
loss of episodic memory. And that's kind of the most
striking feature of amnesia. And what I mean by that
is if you're sitting with an m music participant and
you're having a conversation and you leave the room for
a few minutes and you return, they're not necessarily going
to remember that conversation. They're not going to remember that
you met them, what you talked about, et cetera, and
(22:11):
they also have difficulty remembering new facts, even though they
actually can access semantic memories from before their injury, so
they know who they are, they know lots about the world,
et cetera.
Speaker 1 (22:24):
One of the most extreme examples of this kind of
amnesia is a man named Clive Wearing. He's still alive today.
He's eighty seven years old now, but when he was
forty seven, a virus got into his brain and destroyed
a lot of his hip hook campus. This prevents him
from remembering anything that happens beyond about seven seconds. So
(22:47):
you can have a conversation with him, but after a
short while, he won't remember who you are, what you
were talking about, or even how he got to the
place where he is right now now. Before the virus,
mister Wearing was a musicologist and an orchestra conductor, so
he still remembers how to play music, and he also
remembers his wife and the fact that he has kids,
(23:08):
but he only remembers his kids from when they were little.
Try to imagine what it would be like to be yourself,
but to find yourself in a constant state of not
knowing where you are or how anything around you got
to where it was we're not being able to recognize
any of the people around you, even though they act
perfectly normal, as if they've been hanging out with you
(23:28):
for a while. It's pretty mind boggling. But here's the
other fascinating thing about people with anteror grade amnesia. They
can often still learn new skills. We'll get to what
that means and how we know that after the break.
Stay with us, we'll be right back. Hey, welcome back.
(24:02):
We're talking about the science of forgetting, and so far
we talked about anesia and the different kinds of it.
There's a kind where you don't remember memories you had
before the injury that caused the amnesia. That's called retrograde amnesia.
And there's a kind where you can't make new memories
starting from the time of the injury. That's called anterograde amnesia.
(24:23):
And we also talked about several fascinating things about each
of these kinds. Now, another fascinating thing about anterograde amnesia,
where someone can't make new episodic memories like in the
movie Memento or Dory from Finding Nemo, came from one
of the first cases of this kind of anesia ever studied,
which was a man named Henry Mollison. Henry Mollison, Yeah,
(24:45):
the famous patient HM.
Speaker 4 (24:47):
Yes, exactly. So he was studied for many decades and
this first began in the nineteen fifties. So he had
a surgery in nineteen fifty three to remove parts of
the brain that are really important for memory, such as
the hippocampus as well as the surrounding medial tempor lobe structures,
and all of that was removed in HM in this
(25:09):
surgery to help relieve intractable epilepsies. So after HM surgery,
at first blush, it appeared that the removal of this
tissue had kind of little impact on his cognition, but
it soon became clear that his memory was sort of
somewhat selectively and deeply affected.
Speaker 3 (25:29):
He was profound me in music.
Speaker 1 (25:31):
So Henry Mullison had severe and terror grade amnesia, just
like dor and finding Nemo or Clive Wearing the music
conductor I talked about before, if you met Henry, he
would forget about you within a few minutes of meeting you,
which meant he lived in a constant state of not
knowing where he was or how he got there, But scientists,
namely a researcher called Brenda Milner, soon figured out something amazing.
(25:56):
Henry could learn new skills.
Speaker 4 (26:00):
Come into the laboratory, and he'd be given a new
skill task, but he wouldn't remember ever having been exposed
to the task. He'd come in day after day and
he would perform it as though it was a brand
new task for him, even though he was getting better
over time.
Speaker 1 (26:14):
So scientists learned they could teach Henry new skills, but
he wouldn't remember having learned those skills. For example, you
could teach him to play the piano or to play tennis,
and he wouldn't remember taking the lessons, But the next
time he would sit in front of a piano or
pick up a tennis racket, he'd be amazed that he
knew how to use them. And this is because, as
(26:34):
we talked about before, there are different kinds of memory
in your brain. Remembering things that happened to you, or
the fact that you took music or tennis lessons are explicit,
episodic or semantic memories, but knowing how to hit the
keys on a piano or how to swing a tennis
racket are implicit motor memories. This case of Henry Mullyson
(26:55):
unlocked a lot of what we now know about the
different memory systems in our brain. Now, I talked about
the two basic kinds of anesia, losing old memories and
not being able to form new memories, as if there
are different kinds of anesia, and they are, but according
to doctor Palombo, they often happened together. Patient HM Henry
Mollison had both, as well as Clive Wearing and Dori
(27:19):
in finding Nemo. Okay, we're now going to get to
the last kind of forgetting, which is a condition called
severely deficient autobiographical memory. According to doctor Palombo, this is
similar to interrograde anesia, except it's a condition that some
people seem to be born with.
Speaker 4 (27:39):
So I did some work on what we refer to
as severely deficient autobiographical memory. And my work on STAM
was done in collaboration with doctor Brian Levine, and we
studied a group of three individuals who contacted us and
shared with us that they had profound difficulty or even
(27:59):
an inability to vividly recollect events from their past wow,
but were otherwise healthy and high functioning. And so we
brought these individuals into our lab and we studied them
for a few years, and we studied the way that
they remember episodes to you know, try to see what
we can sort of understand about memory from studying these
(28:22):
individuals who fall at the kind of other end of
the extreme to that of age SAM, who are as
we remember, people who remember quite a lot.
Speaker 1 (28:31):
Okay, if you remember, in our last episode about super memory,
we talked about people with something called highly superior autobiographical
memory or h SAM, who could remember everything that's ever
happened to them in their lives. Well, people with severely
deficient autobiographical memory or as DAM, are sort of the
opposite of that condition. They can't remember anything that happens
(28:55):
to them.
Speaker 4 (28:57):
And so I'll say early days with us as it
is with h SAM, And so our scientific understanding of
SDAM is quite limited. But what we do know so
far is that it seems like individuals with SDAM access
their past in a different way. And so rather than
reliving episodes from their past in vivid and rich detail,
(29:18):
they tend to access their past more through semantic remembering.
Speaker 1 (29:22):
I see it. Could you describe the condition, like what
is it like for them?
Speaker 4 (29:26):
So it kind of depends on the person, and so
some people will describe having difficulty accessing visual images through
their memory. And so it's mainly that this sort of
conscious access to reexperiencing the past is limited or absent.
But yet nonetheless they can access their knowledge about the
(29:47):
world and through facts. And so oftentimes you'll hear individuals
with SDAMS say that they just know their past, but
they're not reliving it in that sort of rich episodic format.
Speaker 1 (30:00):
Like I remember I went to college at the University
of Toronto, but I have no memories of being there
or what it was like exactly.
Speaker 4 (30:08):
Yes, the episodes that can be relived.
Speaker 1 (30:13):
Yes, there are people out there that can remember facts
about their lives, but they don't actually remember living it.
They don't seem to be able to record the kind
of memory that lets you relive your past. They know
they were there, but they don't remember being there. Uh.
It's like I know I had a kid, and I
(30:35):
know they were really young, but I have no memories
of those early days taking care of newbore.
Speaker 3 (30:39):
Yes, exactly.
Speaker 4 (30:40):
And so you have lots of information about your lives,
about your loved ones, et cetera, but it's just you're
not accessing that information through episodic memory.
Speaker 1 (30:49):
Uh, like my record button just wasn't on.
Speaker 4 (30:52):
Possibly it could be that the record button was on,
but it's a different pathway towards accessing those memories. So
that could be right from the get go, that memories
are being laid down in a more factual conceptual way.
That's a very open question.
Speaker 1 (31:08):
Oh, I see they might have the record but on,
but maybe the camera works a little bit different.
Speaker 3 (31:14):
That's right exactly.
Speaker 1 (31:15):
I see, what do you think and this might not
be a scientific question, but what is it like too?
Speaker 4 (31:23):
Yeah, so I think you're asking a little bit about
sort of what the lived experience of ASBM is.
Speaker 1 (31:30):
Yeah.
Speaker 4 (31:30):
I think that's such an important question. And I think
as scientists sometimes we get wrapped up in studying the
nuts and bolts of what memory might look like in
a particular group of individuals, and I think it's important
to take a step back and think about what those
lived experiences are like for our participants. Anecdotally, I guess
I'll say that for some individuals, lacking this re experiencing
(31:53):
component of memory can be hard for them and for
others less so. And so I think in the individuals
we studied, they were high functioning in terms of their
day to day and they were by all accounts healthy.
You know, I think that individuals with STAM feel in
the moment probably as richly and profoundly as the rest
of us do. But it could be that just the
(32:15):
way that one reflects on their past, that there's individual
differences there. So it could be that when you don't
have access to the past in terms of re experiencing episodes,
it might help you move on from the past when
things were difficult.
Speaker 1 (32:30):
This brings us to the last question I had for
doctor Palumbo, which is, why do we forget in the
first place. If it's possible to remember everything that happens
to you in your life, as some people would super
memory prove, why didn't we all evolve disability to remember everything?
What's the point of forgetting?
Speaker 4 (32:53):
Yes, exactly. And that might seem strange because we would
hope that our memory systems would be a perfect record
the past. That would be really helpful in many situations.
But in fact, memory researchers would argue that it is
actually adaptive to forget, and we sort of have this
sweet spot of remembering just enough so we live. We
(33:17):
are encoding experiences at every moment, and a lot of
things repeat in our environment, so we're picking up patterns
in the world, and it's that kind of information that's
really useful to us when we're thinking about decisions we
need to make in the moment or planning out our future,
et cetera. So we actually think that having an imperfect
(33:37):
memory system, a memory system that's flexible and reconstructive, is
actually really good for us.
Speaker 1 (33:43):
Yeah, I guess the idea is that your memory is
meant to be a little fuzzy so that you can
see the larger patterns in your life.
Speaker 3 (33:52):
Yeah, that's a really good way to put it.
Speaker 1 (33:54):
So you don't miss the forest for the trees.
Speaker 4 (33:57):
Kind yes, exactly exactly, because we all didn't have to
make really quick decisions, especially if we're being threatened by something,
and so we want to know how things generally occur,
not necessarily how they occurred just once.
Speaker 1 (34:11):
I see, like, we don't get hung up on whether
the tiger running at you have the same stripes as
the last tiger you saw a few weeks ago. You
just want to remember it it's a tiger. At least
you run away.
Speaker 3 (34:22):
That's exactly right.
Speaker 1 (34:23):
Yes, oh interesting, So there's a reason I'm forget that.
What we're saying, there's there's a good reason, very.
Speaker 3 (34:29):
Good reason you're forgetful.
Speaker 1 (34:30):
Yeah, yeah, all right. That was a lot of information
about memory, amnesia and forgetting. But the good news is
that if you don't exactly remember the things we talked about,
you can just get the replay button and you'll get
to relive these conversations all over again. It's like our
phones and our computers are now part of our extended memory.
(34:53):
Thanks for joining us, don't forget to come back next week.
See then you've been listening to science Stuff. The production
of iHeartRadio written and produced by me Or Hitcham, edited
by Rose Seguda, executive producer Jerry Rowland, and audio engineer
and mixer Kasey Pegram. And you can follow me on
(35:15):
social media. Just search for PhD Comics and the name
of your favorite platform. Be sure to subscribe to Sign
Stuff on the iHeartRadio app, Apple Podcasts, or wherever you
get your podcasts, and please tell your friends we'll be
back next Wednesday with another episode.
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