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PROFESSOR: In some ways, I won't be able to compete with
live demonstrations of children from last week.
But I will try to talk about adult development.
And we will really sweep through your minds and brains
from when you were not yet born until you're going to be
in your '90s.
So here's your life from the beginning to the end viewed in
different ways.
And we'll touch on a number of different topics.
So you know this question about people have talked for a
long time about the development that one goes
throughout one's life.
What walks on four legs in the morning, two legs in the
afternoon, three legs in the evening?
You know the answer to this, right?
People.
They're crawling, they're standing up, and then
you get to my age.
And we need an extra little prop to move around
successfully.
So sort of thinking about this, that different things
matter to people at different ages, that there's different
priorities, different ways of thought.
Erik Erickson is often given credit for trying to
articulate that.
And we'll just walk through it for a moment.
Where he said at different ages, at infancy, early
childhood, through school, adolescence, young adulthood,
people are dealing with different kinds of issues and
different developmental tasks in front of them.
Your life is a constant development.
Not maybe as dramatic as infancy where we saw last time
that children really see the world differently.
But there's different challenges in front
of you at all ages.
At infancy, you're deciding who can you
trust, who can you love.
Is it a good world?
And then the drama of potty training, independence.
How much are you becoming a free agent in the world?
Early school, where you start to interact with other
children, and play, and make friendships, and think about
social groups.
Later in schools, you're becoming more advanced in
terms of what you're learning in school and more complex in
terms of the social networks that you're developing.
We'll come back to this at the end, a period of high anxiety
and drama of adolescents.
Then there's something about young adulthood.
You may have heard recently people are speculating that
what used to be the beginning of young adulthood culturally,
at least in the US, and maybe Europe, and industrialized
parts of the world, that whereas the '20s used to be
considered a decade of adulthood, there are now
theories floating around or impressions floating around
that '20s are the new adolescence.
What are you guys think?
Everybody says, oh my '20s, I'm going to discover this and
discover that.
But when I get to 30, that's when we're playing for keeps.
Is it?
Well, and part of it's because you live longer, on average.
Or you count on living longer.
And you do, on average, live longer.
For a person who's counting on living to 90, which many of
you are sort of, another decade of finding your way,
your 20s, seems reasonable.
In a world where people didn't live nearly as long, didn't
have as many options, by the time you finished college--
or many people didn't go to college-- it's roll up your
sleeves and get to adulthood.
So there's all these sort of magazine discussions, are the
20s the new teens in terms of whether people feel they have
responsibilities they have to execute as a young adult.
And this a little bit timed also, a little bit
anachronistic, then having a family.
Although, I think we're much more thinking about that's not
necessarily the root for everybody at all.
And then old age where you give other
people lots of advice.
So we're going to talk about brain development from infancy
to young adulthood, cognitive stability
and decline in adulthood.
We've talked a little bit about that.
We'll talk a bit more.
Alterations in hemispheric specializations
that come with aging.
A bunch of remarkable results about exercise in the brain.
All of us want as we get older, or just even when
you're younger maybe, just a pill you pop and
you're ready to go.
That would be the best.
It turns out there's remarkable evidence about what
physical exercise does for the brain.
I'll share that with you-- especially in regards to
aging, but at all ages--
ideas about how as you get older, your social and
emotional goals will tend to change, a little bit about
rewards, and a little bit about back to adolescence and
some thoughts about what's going on in the adolescent
mind and brain.
So we know if there's one thing about the brain that's
stunning, and challenging to grasp, and empowers us to be
humans, it's this complexity.
There's a huge number of neurons, fantastic number of
connections among the neurons.
So there's just a phenomenal complexity that all starts
with a single cell.
And how does the brain become this
dramatically complex organ?
And how does it organize in the right way to let you be an
effective learner, an effective partner in your
family, and so on?
So we start with the idea of neurogenesis, a magical word,
the neurons being born.
And they have to make this crawl, there's a huge path the
size of a neuron from the ventricular surface, the
ventricle, the fluid-filled space, to get to the place
you're going to be in the brain.
It's a huge adventure per neuron.
Cells dividing there, the earliest neurons are existing
by the second embryonic week.
So that's when you began to produce your
neurons in your brain.
By the seventh embryonic week-- so you're just two
months of pregnancy--
you're producing an estimated 500,000 neurons a minute.
We said the neuron is kind of like a moderate computer.
Except unlike iPhones, it can't keep track of where
you're going all the time.
We said it's a moderate computer.
So 500,000 of those every minute, I mean, staggering.
That it all works out is staggering.
By the 18th week, you've mostly made all the neurons
you're ever going to make for the rest of your life except
in two brain regions.
And there's been a big debate in the last decade about
another brain region.
I'll share those with you.
But people have been taught for many, many, many years in
medical school, and college, and graduate school, that all
the neurons you get are by the 18th week.
So hang on to them through healthy
living and wise behavior.
Because you have what you have, right?
So don't lose them.
But we'll talk about that you lose the vast
majority of them anyway.
I still recommend healthy living.
Because you know, perhaps from other courses, that the brain
does this wild thing.
It excessively overproduces, by massive scales, the number
of neurons and the connections among the neurons.
And then through use, it gets rid of neurons and gets rid of
connections among neurons.
It's exactly the opposite way if you build a building.
If you build a building, what do you do?
You construct every bit of it you need, and you're done.
Well you don't do is say, I need a two-story building.
So I'm going to do a 40-story building or a 90-story
building and then knock off the stories
as they're not needed.
You say, well, that's wild.
Why would I do that?
But the brain brilliantly makes many more neurons and
many more connections on epic scales and then only uses the
ones that seem to be useful for the
functions of the brain.
And so for that reason, the density of the neurons in the
brain is much higher in a two-year-old than in you,
where it was much higher when you were two than it is now.
So in a two-year-old, they have 55% more gray matter
density in the frontal lobe than an adult.
Even at age five, even at age seven,
they're 10% percent more.
From a peak of around before birth, you're constantly
shedding neurons and their connections and keeping the
ones that seem to be effective somehow.
Now, for many years people said, is there neurogenesis in
the adult brain?
Is everything you get before you're born and
that's pretty much it?
And there's many reasons to be interested in that.
One is just how does the brain work?
How do people work?
The second is for diseases like Alzheimer's disease,
Parkinson's disease, and other diseases.
We would love to replace neurons that have died to help
people do better.
So can the brain make new neurons before birth?
There's compelling evidence in animals, and some indirect
evidence in people too, that neurogenesis does continue
into adulthood in the olfactory bulb and in this
particular part-- and I'll come back to this-- in the
hippocampus, a small part of the hippocampus called the
dentate gyrus.
Everybody's in pretty much agreement on this for the
moment, which is kind of interesting.
Why those two areas amongst all the areas in the brain?
What makes them different that they can produce neurons all
throughout your life?
And then about a decade ago, Elizabeth Gould at Princeton
said, oh, when I do the right kind of experiment, I see new
neurons in the prefrontal cortex of monkeys, and for
human primates.
That was a giant revolution.
Because they said, wait a minute.
Maybe if monkeys are doing it, people might be doing it,
making neurons throughout their life.
We just did know that.
It's not so easy to measure.
If you think about it, the kind of experiment to know for
certain if a human is making a new neuron is not so easy.
Because brain imaging is very far from the
single neuron level.
And even if we saw a neuron, how could we tell it's new?
And then Pasko Rakic, a big developmental researcher at
Yale said, that what she really saw was glia.
The glia are the other cells in the brain, not the neurons.
They support the neurons.
Everybody agrees that you make glia all through your life.
There's no debate about that.
But glia are not the stuff of thoughts and feelings.
Neurons are.
So what do we understand about that whole story?
Here is an unbelievable experiment, I think.
It's really not an experiment.
But it's a measurement.
Published in 2006, it's one approach to asking, do adults
make new neurons?
So the nuclear bomb tests that occur during the Cold War sent
a carbon-14 into the atmosphere from 1955 to 1963
until there was an international test ban treaty.
And then these decreased and stopped.
But there was a lot of nuclear bomb testing in the
late '50s and '60s.
That released carbon-14 into the atmosphere.
And that integrates with DNA and forms a date mark for the
cell of a birth.
So this is not an experiment we would want to do again,
atmospheric nuclear testing, and having nuclear stuff
floating around in the atmosphere.
I'll tell you the bottom line, and I'll show you how they
figured this out.
What they figured out is looking at people who died a
few years ago, that
nonneuronal cells are generated.
That was found before glial cells are made throughout your
lifetime is the inference from the finding.
But neurons are not generated in adult neocortex.
The commentary in this article said, no new neurons for you.
OK, that's not quite true.
We know these two little areas in the brain do it but not in
most of the brain.
And they also looked at something called BrdU,
B-R-D-U, which is another way to take a
brain if you have it.
It marks newly synthesized DNA.
So if you have the brain directly to measure it, you
have a couple of measures of newly synthesized DNA, which
would be the marker of new neurons.
So here's a fantastically interesting thing.
They took people who were born in different times, took
postmortem samples, and measured carbon-14 relative to
what was expected--
there's a line here-- it was relative to what was expected
by the amount of carbon in the atmosphere.
And here's what they found.
If they look for somebody born after 1963, they have, in
their neurons, exactly the amount that you would expect
if they made all their neurons around here and the decrease
here didn't affect the neurons at all.
The glia are here, which is kind of an average of here and
the rest of life.
So if you measure the average age of the glia, it was about
the average age of the life of the person the carbon was
being picked up in the DNA, because it's being made.
It's being kept, and being made.
But the neurons all looked like one value, the value that
has to do with when you're born.
So it's not changing the number of neurons that are
showing the carbon-14.
As if whatever you've got at birth, that's it.
On the other hand, here is somebody born before 1963,
having essentially zero carbon that's being showing up in
their neuronal DNA, and having again the expected average
glial DNA as if glia kept going.
So this is fantastic.
It's looking at the carbon-14 in the DNA of neurons and
glial of people who have passed away.
And saying the carbon-14 dating looks like neurons.
You get them all before you're born.
That's it.
Glia, you keep making.
And they can look at it more directly by looking at this
thing that shows you recent DNA, again, showing you
impressively that glia keep making new glia with new DNA
but not new neurons.
So the current conclusion in the field, as far as anybody
can tell, is no new neurons for you except in your dentate
gyrus and olfactory bulb.
Now here's something fantastic though.
It appears that exercise--
I'll just show you one example in animals and humans--
there's evidence that exercise will pump up the number of new
neurons you make in the dentate gyrus of the
hippocampus.
And we know that the hippocampus is
important for memory.
So that's not a bad place to make new neurons.
So you know that going to exercise will strengthen you
in various ways.
But you never realized, unless you follow this line of work,
that when you exercise, you're enhancing the number of new
neurons that you're producing in your dentate gyrus.
So here's a couple ways people have approached this.
So one way is to measure cerebral blood volume, how
much blood is in the dentate.
And I'm going to show you evidence that mice that are
allowed to exercise push up the blood volume.
And that seems to go with direct evidence of
neurogenesis.
Because you can do that in the animals.
You can look up sacrificed animals.
And then in humans, some indirect evidence that
exercise is, again, pushing up the blood volume in the
dentate and pushing up a little bit of memory abilities
that go with the part of the brain.
We can't go in and measure neurons in the humans.
So here are mice who exercise or didn't exercise.
They measured the blood volume.
Here in red is the dentate part of the hippocampus.
You can see it's the hottest spot for blood volume.
And it's the only part that responds to exercise.
So they had some mice not get to exercise,
some mice get to exercise.
The blood volume increases within the hippocampus
selectively in a small component of the hippocampus,
the dentate gyrus.
Exercise is pushing up the blood volume.
Now that's not direct evidence about what's happening at the
cellular level.
But they can sacrifice these animals and show you that if
you look at this binding that goes with new neurons, with
new DNA, that's pushed up the exercise animals.
Here's the statistics.
Here's the picture.
So in the animals, they can correlate directly.
More blood volume and more new neurons going with more
physical exercise.
In humans, they can measure the blood volume.
And so they had some people do more exercise, some people
less exercise.
Again, it was a dentate gyrus selectively.
It showed an increase in blood volume in humans.
And now they give them a memory test.
And it's not overwhelming.
But at least in some cases, the people who did exercising,
who pushed up their blood volume, also pushed up a
little bit their memory performance.
So in humans it has to be more indirect, but all the data
aligned with the idea that exercise is pushing up your
own neuronal genesis, the creation of new neurons in one
of the two regions everybody agrees we make new neurons,
the dentate gyrus and the hippocampus.
But cells have to go incredible distances at the
cellular size.
Neurons have to travel to the intended location.
Migration occurs over many months including eight months
postnatally.
Here's this neuron following it's little path to where it's
going to go.
There's glial tracks following molecular cues as to their
ultimate target location to get organized.
Its initial destination and function are predetermined at
the start of the migration.
People can measure things in these that tell you where this
is going to end up.
It's programed in these cells.
Unless there's something that blocks them, they know where
they're going to go and make up different
parts of the brain.
And then they form synapses, the part where information is
sent from one neuron to another.
It occurs throughout the brain, but at different rates
and different areas.
So very early, you see it in spinal cord.
Very late, you see it in higher cortical areas like
prefrontal cortex.
At the peak growth, there's an estimate-- these are all gross
estimates--
that you may be forming 1.8 million synapses per second.
It's stunning, 1.8 million synapses per second.
And do you know how many molecules are in an average
synapse by current estimations?
1,000.
There's 1,000 different molecules in a synapse for it
to do it has to do.
Multiply that times 1.8 million per second.
It's spectacular biology.
And then they keep getting more and more until two years.
And then you start just losing them.
By age 16, you'll have lost a lot of them.
And so the people have this idea we mentioned before,
pruning and selection.
That we overgrow the number of neurons, the number of
connections.
What stays is activity dependence, or this use it or
lose it neural Darwinism.
Here's something amazing.
There's an estimate that we lose 20 billion synapses per
day through adolescence.
And that's not a bad thing.
That's not the worst behaving adolescents doing the worst
things they can do.
That's the brain getting rid of
connections that aren't useful.
It's an incredibly interesting way to
construct a powerful brain.
It's to get everybody to way overbuild.
And then eliminate the ones that aren't powerfully useful.
And another marker of development is myelination.
That's the growth of the fatty sheath that surrounds the
neurons that are extending distances.
It insulates them and accelerates their signal.
It looks like white matter in the postmortem brain.
What happens through adolescence--
here's age four to 22--
is that white matter goes up, and gray matter goes down.
So quite interesting, the total brain size from about
age six to about 20-- young adulthood, most of you--
stays about the same, the total brain size.
What you're doing is you're getting rid of gray matter.
And you're enhancing white matter.
You're getting rid of the neurons that are nonproductive
and the synapses that are nonproductive.
And you're increasing the strength with which different
parts of the brain can communicate with one another
through the white matter.
And so here's the kinds of pictures of this growth.
And some of the parts of the brain that mature latest by
these kinds of measures of getting rid of the overgrowth,
are in prefrontal cortex.
And we've talked about that before.
So many people are interested always in thinking about
developmental issues and the biology of them.
And here's a kind of a stunning finding.
And we don't know exactly how it would relate to humans.
But I thought it would be interesting to share with you
and think about this just a little bit.
So the title of the paper in science was "Good Memories of
Bad Events in Infancy." So we know from before, and just
common sense, that fear is important for the survival.
So we start at the amygdala, which seems essential for
learning what's to be feared.
Because what's to be feared is what injures you, or worst
case, could kill you.
So the amygdala is essential for learned fear.
And we know that one example, a fear condition that depends
on the amygdala, would be a neutral
stimulus like an odor--
odor that's not particularly good or bad, just an odor--
and then a shock that makes an aversive stimulus.
So you pair them through conditioning, odor, shock,
odor, shock.
So the odor predicts the shock.
Now, they looked at young rats and looked at attachments.
And here's what they find kind of remarkably.
Up to postnatal day nine for these rats, if they were
exposed to the odors and the shocks, here's what they do.
They know through pairings odor, shock, odor, shock,
odor, shock, here comes the odor.
Here comes the shock.
They still approach the odors.
That's what's in this graph.
Up to nine days, the rats, the mice--
sorry--
are still approaching this odor even though it will lead
to a shock.
But on the 10th day, just one day later,
it completely reverses.
And they avoid the odors that predict the
shock, a complete reversal.
So they keep going to the odors with the shock.
And on the 10th today, the pups stop going there.
And what they also find is this.
If they look at metabolic activity in the amygdala, for
the nine-day olds, it's the same for the odor and the
shock, where a neutral order.
It's not selective to what's to be feared.
And the 10-day old, here's a big response in the amygdala
for the odor that predicts the shock, for the fearful
learning, to know what's scary, and
injurious and dangerous.
So how do people think about this?
Well, this is an animal experiment up to nine days.
We can't really know how it relates to people.
But the speculation was this.
And maybe there's something to it on a
different scale on people.
Why would an animal approach something injurious, up to the
amygdala seems to get more mature, and then
avoid what's injurious.
Why would that happen in such a predictable evolutionary
determined way?
And the hypothesis is this.
That if you're a very helpless newborn, you have to go to
things no matter what.
Because you're so dependent on things in your
environment to survive.
But at some moment you mature enough that you
say no thank you.
If it's going to be shocking and painful, I'm
going to avoid it.
You become kind of independent in that sense, in
the concrete sense.
And so the author said, well, could it be helpful for
newborns to know, no matter what, approach a caregiver,
not respond to things that are negative, because you need the
care, because you're so dependent.
And now this is super speculatively.
A thing that's been noted is that even in families where
there's unfortunate tremendous abuse for a young child, the
abuse victims so commonly remain powerful
loyal to their parents.
Is this kind of a mechanism that mixes up attachment and
fear especially when you're young and can't separate them
out so well?
So it's a huge leap from the mice to the people.
But it's a mechanism that we can understand might be
involved in how attachment and fear can have unusual
relationships with one another.
All right.
You can't avoid reading in the newspapers, or seeing on your
computer screen, discussions about the deficit and older
people like me demanding a lot of medical care that's paid
for by the wages you're going to get in a couple years.
I mean that's how I look at it.
So you are entering a world, we're all entering a world,
where the changing ages demography of our society is
spectacular.
Japan is ahead of us in this a little bit.
The rest of the world is following.
And China is going to be unbelievable when
it happens on scale.
But the United States right now, right now.
And here's why.
For most of human history, the average life expectancy was up
to 20 years old.
That's why you had to be an adult.
Because at 20, who knows how much time I have.
I better do my adult things.
Some people lived for a long time.
This is really interesting.
It wasn't that everybody perished by 30.
Some people lived to 60, 70, 80, 90.
But many people fell ill to many diseases that are now
readily cured.
So the average age was 20.
In the 1800s, it became the '30s, just a couple hundred
years ago in all of human history.
By 2000, the average person in the US lived until 77.
By 2010, 78.
So we're having a spectacular growth in the proportion of
humans in our society who are living a long, long time,
which is a wonderful thing.
But it's radically changing the world we live in and the
world for those people who are older as well.
So, for example, 100-year-old people, there's 50,000 of them
in the US, which is triple what there was a time ago.
And it's expected to be a million people in the US who
are 100 years and older by 2050, which is in your
lifetime, a million people in the US alone
will be 100 or older.
And maybe 50% of girls born in 2000 will live for a century.
Spectacular changes are occurring right this moment.
The baby boom generation, huge numbers of us are approaching
retirement and the kind of medical support that gets
heavier when you get older on average, huge numbers of us.
How's it changing?
One way it's changing is that families often have-- and you
might hear this-- an issue of families feeling that they're
a sandwich generation.
They're taking care of their children and the elderly.
And you can bet if you have parents who are living to 120,
you're doing that.
Giant effects on education, pension, work, financial
markets, I mean these are epic societal effects.
So you're hearing the discussion now about how the
US is going to deal with this.
So there used to be kind of an old model.
And even this is not that old.
This is from the mid-1950s.
Your job was to go to college, have a career, have a mate,
take care of a kid, retire at 65, and put your
feet up on the desk.
But all of a sudden, if everybody's living--
not everybody, but huge numbers of people are living--
until 70, 80, 90, 100, many in pretty good health-- not
everybody we wish for-- but many in pretty good health,
that's a fantastically different thing.
65 is no longer the retirement moment, and you're
glad you made it.
65 is something like the halfway point of your
potential work life.
20 to 60, 60 to 100, something like this.
It's an unbelievable change.
You cannot overestimate how it's changing the world around
you, and how it will affect the economics and the politics
of the world that the rest of us will be in for many years.
There's about 10% of the population over 65 now.
In 20 years, one out of every four people will be over 65 by
current estimates.
So we're going to elect whatever president we want.
And older people go vote a lot more than younger people.
You can change that.
But that's how it is.
So let's talk about adult development.
I can tell you that if you compare adult development,
very little is understood from 20 to 80.
Almost all the research is taking something like college
students, and something like 80-year-olds,
and comparing them.
So pretty much minimal information is available about
everything between 20 and 80.
But we'll look at what we can.
And one of the things we'll talk about for a moment is the
two kinds of studies we could look at for development.
This could be about infants.
But we're going to talk about adults.
Cross-sectional versus longitudinal, so
cross-sectional is I look at you as 20-year-olds.
I look at some 80-year-olds in the Boston community and
compare them.
That's very different than looking at you at 20 and
seeing you at 80.
Because that's much more controlled.
That's you with everything that's special and particular
about you at 20 and 80.
When you go get people who are 20-year-olds from one place
and 80-year-olds from another, a cross-sectional , study,
that's going to have all the differences that
go with those cohorts.
So what do we see in these kinds of things?
So here's some measures.
You've seen this kind of stuff before.
For things like working memory, speed of processing,
and long-term memory.
Here's people in their '20s, people in their '80s, a ski
scope of decline.
Here's things like knowledge of vocabulary.
And that stays more steady, so the crystallized fluid
distinction you've already heard about before.
So what are the strengths and limitations of cross-sectional
versus longitudinal studies.
So for cross-sectional studies, they're fast.
If you're a scientist like a graduate student who has to do
a Ph.D. thesis in a mere six or seven years, you can go to
experiment with 20-year-olds and 80-year-olds and have a
conclusion.
If you're a graduate student who would have to test this
class of 20 and come back to you in 60 years from now and
see how you're doing, that's going to be slow progress.
So that's why an overwhelming amount of evidence is
cross-sectional.
The problem with it is cohort effects.
We discussed, for example, that IQ scores go up year by
year throughout the world.
So you're not really comparing equal things in terms of
educational opportunities, nutrition, exposure to
information on the internet.
A 20-year-old and an 80-year-old have lived through
different worlds.
So it's all mixed up in the measurements.
Not just age, it's different worlds that
people have lived in.
Longitudinal studies are painfully slow.
They're more accurate, because you're looking at change
within a person.
You're holding all the world things constant.
You have one other weird thing, which is you get
practice effects.
If you test somebody in the same test, if you're 60 years
apart, you don't get much.
But if it's maybe three or four years apart, you take a
test twice, you get better at it.
So that's a problem with longitudinal affects when you
retest somebody.
So there's been a few studies that have looked at relatively
short-term longitudinal and cross-sectional data.
And here's a ski slope on the values of fluid
intelligence things.
And it's just made a bit milder by a longitudinal
design, but not dramatically different.
So it's not the case of longitudinal studies.
People used to think oh, these longitudinal studies are
overestimating that.
Especially if you're older, you like that thought.
It's a messed up study approach.
But unfortunately, cross-sectional ones just
diminish the difference a little bit.
So people have said, though, there's
an interesting trade-off.
What's the trade-off, then--
I'll ask you for a moment--
between most of you are like 18 to 22.
I'll bracket it 17 to 25.
Is that fair?
What advantage do you have versus somebody in their
mid-'50s like me?
And what disadvantage do you have in some global sense?
Oh.
That was painful.
The answer was you guys are physically able.
All right.
That would be true.
There's not many Olympian sprinters who
are in their mid-'50s.
How about in terms of cognitive things?
So we just said, for speed of mental processing,
it's good to be 20.
And then 30-year-olds are a little slower.
40-year-olds, a little slower.
50, 60, 70, every decade a little bit slower for speed of
mental processing.
But there's one thing that's an advantage
with time for cognition.
What's the advantage?
AUDIENCE: [INAUDIBLE].
PROFESSOR: Sorry?
AUDIENCE: Experience.
PROFESSOR: Experience.
Thank you.
Oh yes.
Yes.
Over time, you learn stuff, especially stuff that you're
exposed to a lot.
So time is a trade-off within adulthood.
You lose some speeded capacities.
You gain some specific knowledge or experience.
So they looked at studies like these, air traffic
controllers in Canada.
And this is very relevant.
Especially now, air traffic controllers are in the news
more than they want to be.
You've seen them?
Unfortunately, they're napping.
They're playing movies, some of them.
I'm sure it's a tiny minority.
But it's worrisome if you're a member of the flying public.
So here's another question.
At what age should you tell somebody, well, I think we
don't need you to be an air controller anymore, because
you're not with it enough for us to feel safe.
So people are probing this all the time.
The average retirement age in the US is 55, in Canada, 65.
Is one more correct than the other?
And so here's what they found when they looked at air
traffic controllers.
Age influences processing speed but not task
performance.
So what we're thinking is older people aren't better.
But they're not worse.
Maybe there's a trade-off between speed and experience.
And it kind of evens out until some age where it will no
longer even out.
118 pilots, 40 to 69, they took place in flight
simulators and tested three times across three years.
It's a longitudinal design and a flight simulator.
The older pilots were worse the first time they did it.
Now some time is passing.
But then they outperformed the younger pilots in
years two and three.
That is, once they had some experience with the new
situation, they could apply, presumably, their prior
experience.
But the very first time they did it when they have to use
their fluid intelligence to figure out what's going on,
they were worse.
So you can see some trade-offs between raw processing, speed,
and flexibility that goes with the young adulthood and some
degree of knowledge and expertise
that's gained over time.
There's trade-offs on these things.
How about in memory, declarative memory that we
talked about, every day memory.
I'll show you in a moment.
There's mild, steady decline in healthy aging severe in
Alzheimer's.
Implicit memory, we talked about that.
It can be more steady across ages.
But let me focus on explicit memory, declarative memory.
We're going to figure out why the projector is washing these
things out so much.
But here's a slide that you don't have to see
very much to know.
Long-term memory performance is going down quite sharply
year by year as you get older.
But here's something that was a huge surprise from brain
imaging, a huge surprise.
And the thing that if you didn't have brain imaging, you
wouldn't even conceive that it could have existed.
So many studies have done brain imaging as people
perform various kinds of tasks, memory tasks in this
case, with young adults and older adults.
And
what they found, unexpectedly, was this.
Young adults would typically activate one side of the
prefrontal cortex typically in regards to whether it was
verbal or spatial.
So here's young adults mostly on one side, mostly on one
side, mostly on one side, mostly on one side.
Healthy older adults in good health characteristically
turned on both sides of the brain as they were performing
these memory tasks.
So you wouldn't have known that if you didn't have
imaging, because who could have thought about that?
So then there was a little bit of a debate in the field with
the fact that adults were turning on both sides of their
hemispheres whereas adults were just picking one
or just using one.
Was that a good thing or a bad thing?
So people said, well, it's a bad thing.
Because maybe as you get older, you lose your
specializations, and you're using the wrong stuff.
It's as if I need my physics book.
And I'm going to grab my chemistry book.
Well, just grab your physics book.
Just grab the right thing.
Why are you getting other stuff that's not relevant that
could mess you up and slow you down?
So some people said, you're sort of losing the
specializations of peak young adulthood.
You're leaking brain activity in the wrong places.
It's yet another sad sign of getting older.
Here's an alternative one.
Well, you get older.
But maybe you get some compensatory mechanisms.
You realize at some level in your brain that you can't do
what you could when you were 20.
And you make up for that by somehow using two sides of
your brain instead of one.
So that would be a good thing.
So how would you decide that?
How would you decide whether using the two sides of your
brain when you're an older adult is a helpful thing, part
of the solution to keeping your cognition going, or is it
part of the problem of losing long-term memory abilities as
you get older while they're declining.
How would you decide that?
There's kind of an easy answer.
AUDIENCE: [INAUDIBLE].
PROFESSOR: Sorry.
AUDIENCE: [INAUDIBLE].
PROFESSOR: You what?
AUDIENCE: Like, split their brains.
PROFESSOR: Yes.
It's a suggestion we should take older people, split their
brains, and see how they're doing.
Well, older people, their long-term
memory is not that bad.
So here was the approach.
It seems reasonable.
They say amongst older people, some people do better and
worse in terms of the memory.
Does better memory go with using two sides or one side?
And what was found, and here's one example.
Here's young people using one side of their frontal cortex
as they perform a memory task.
Here's older people whose memory was not so good.
Here's older people whose memory was good.
And here's a similar finding.
So the suggestion was that older people who used both
frontal cortices were actually doing better.
They were having less of an effective age on cognition.
So the answer seems to be, it's a good thing.
And if you're older, you somehow compensate for some of
the decrease in long-term ability by applying more
neural systems to support your performance.
Older adults are really interested in this.
You are not.
In about 30 years, you might be.
But older adults are really interested in what can I do to
keep myself going?
Because I'm going to live to be 80, 90, or 100 with just a
little bit of luck.
How can I keep my quality of life high in terms of
cognition and mental abilities?
So one thing that people have found is that, on average,
higher education is correlated with-- and there's many
interpretations of this--
better cognitive abilities and less likelihood of getting
Alzheimer's, or getting Alzheimer's, if you're going
to get it, at an older age.
So that's kind of interesting.
It's good to go to college.
It's good to keep being educated in some sense.
It doesn't have to be formal.
But formal education correlates with that.
Now here was a surprise.
And now you tell me what it is.
So how would that work?
How would sitting there and listening to me really
carefully right now give you an extra decade of cognitive
ability when you're 80?
All right, now I've got your attention.
How would that work biologically?
Is education kind of going in your brain and saying, we're
knocking all these things in.
And we're keeping them here.
And we're not going to let you have any injury when
you're 40 or 50.
How does that work?
So I'm going to tell you one more piece of information,
which is this.
And you tell me what you think.
So the other thing that we know is there's evidence that
once you get the diagnosis of Alzheimer's disease, then the
more educated you are, the faster you decline.
And I don't think the story is all done yet.
Because people are complicated.
But this is the current evidence.
So how do you interpret that?
So here's the interpretation.
The interpretation is more education gives you more
mental tools, what people will call cognitive reserve.
You have more things going for you like maybe the ability to
use two hemispheres.
That will protect you as something like some brain
injury happens over time, like an Alzheimer's disease, or
other causes of slowed or diminished
cognition in old age.
That will help you.
You have more tools with which to keep operating
successfully.
But once Alzheimer's disease become severe enough in the
brain that those tools are no longer available to you, then
the more educated you are, the more you plummet.
Because everything's done.
So we now know something-- and I'll just say
a word about this--
Alzheimer's disease-- and this is compelling
evidence for this--
starts in your brain about 15 years
before you get the diagnosis.
And it could be more than that.
That's how far we can track it back by brain imaging.
So if an adult is diagnosed with Alzheimer's at 70,
somewhere around 55, something has started that will
ultimately be injury enough to lead to dementia and
Alzheimer's disease.
And that's why there's such a big emphasis on early
identification.
Because it's very hard to treat a brain that's
had a lot of injury.
You want to catch the people at 55 or 60.
So we also know that lifelong cognitively is good.
Conscientious, we talked about that.
And here, again, comes exercise.
So they took a study.
This is now a random assignment study, finally a
full on experiment, where they took sedentary people, people
who were not exercising over 60, and assigned them to two
groups, an aerobic training group who did walking and
swimming, so some really exercise, and non-aerobic
group who did toning and stretching.
So they thought they were special.
They were active.
But they weren't doing the aerobic exercise.
And they didn't do it a phenomenal amount of time, an
hour a day, a few times a week for months.
It's not a brutal exercise schedule.
What happens?
It's kind of amazing what happened.
These are healthy people but not very active.
What's shown here in the red bars are the cognitive
performances after the exercise of the
healthy older people.
And blue bars are the people who did the stretching and
toning, not the aerobic exercise.
So very substantial gains in cognitive abilities from a few
months of moderate exercise.
And in the brain, both by functional MRI and by
structural MRI, in gray matter, and white matter,
physically measurable changes in the brain for the group
that did the aerobic exercise a couple times a week for a
few months compared to the group that did
the less active exercises.
That's amazing.
The brain changes.
Cognition changes.
Again, no pill you can pop.
And you're making new neurons in your dentate gyrus to boot.
So all of us want the easy out.
But exercise is the most compelling story for keeping
your brain optimized that we know.
Now here's a remarkable thing.
Exercise, we kind of get.
Actually, if you think about it, we don't know the
mechanism at all.
I mean, you're running around like this.
Now how is that pushing up your neurons in your brain?
But here's something very psychological
that's kind of stunning.
And at first, I almost didn't believe it when I read it.
But there's been a few other studies that
have supported this.
We often think, well, exercise is something real.
Attitudes, even in a psychology course, attitudes,
they're just attitudes.
So look at this.
And then you can think about this.
So they looked in a longitudinal study of over 400
in the Baltimore Longitudinal Study of Aging.
They started under 50.
But they kept going with them.
They gave them a questionnaire on attitudes about aging.
So they said, are older people, for example, more
absent-minded or less intelligent?
And some people say, oh my gosh.
Older people are very absent-minded.
They're very less intelligent.
Other people think it's just a milder think.
People vary in their estimates of how severe these changes
are in old age.
Then they measured something very concrete and real, the
number of cardiovascular events, like stroke or heart
attack, over the next 38 years.
So this is a real physical measurement.
This isn't an attitude.
How powerful is an attitude?
Well, it's kind of stunning, unbelievably
powerful in some ways.
We don't know if it's the attitude or something
correlated.
But here's the percent with strokes or heart attacks.
Here's the people who had negative age stereotypes.
And here's the people who had positive age stereotypes.
So one always has to be worried about the
chicken and egg issue.
Maybe if you had a lot of strokes and heart attacks,
you're not so optimistic about your old age.
But they were measuring these things at the beginning, they
were very similar.
So they weren't starting out with
different health problems.
So something about attitudes seems to chip in to the most
core aspects of physical health.
But none of us understand the mechanism.
Yes?
AUDIENCE: Wouldn't family history have a
lot to do with that?
PROFESSOR: So the question is how about family history?
It could be mixed into that.
AUDIENCE: [INTERPOSING VOICES].
PROFESSOR: Yeah.
That's a very good.
Then it's not just attitudes, right?
Or it could be not attitudes it all.
And here's the concept.
That regardless of your age-- but age is one of the most
powerful pieces of the story--
when your time is limited, people focus on social goals
related to emotional meaning and emotional satisfaction and
less related to knowledge acquisition.
That depending on the moment of your life on average, when
you're in adolescence, and you're in college and graduate
school, and you're beginning your residency, or becoming a
junior partner at a law firm, you're at an age of huge
information acquisition.
What you want to know is what do I need to know to do
something important, significant,
valuable in my life?
You're sitting here acquiring knowledge.
College is four years of acquiring knowledge in terms
of classrooms and majors.
You guys do other things too.
But the number one mission is acquire that knowledge.
Now when you get older, you don't really want so much
information anymore.
And maybe what you're much more interested in is how you
regulate your feelings, how positive can you make your
life, not by being adventurous, taking risks, and
all this kind of stuff, but by finding
a way towards happiness.
And I'm going to show you a bunch of research that
suggests that young adulthood is full about acquisition of
information through adventure.
And old age, on average you're focused to regulate your
emotions in positive ways.
And so sometimes people will call that wisdom.
Although, you could just say it's different things for
different ages are desirable.
And part of the support came from the following result,
which has been found many, many, many times.
But it was kind of stunning when it was first reported.
So this is where people were asked, how happy are you?
Are you satisfied with your life?
So here's a younger adults, 18 to 50 basically.
About half of them said they're very satisfied.
But it zooms up if you're older.
How many people are satisfied with their standard of living?
40 if you're younger.
60 if you're older.
Frequency of depression, for example, never.
Let's pick often.
It's higher for younger people.
They have more frequent thoughts about suicide.
By every measure you can make, if we give you a questionnaire
like this, on average, for 20-year-olds or 30-year-olds,
you would report more unhappiness than older people,
on average.
Of course, it varies.
But that's kind of a surprise maybe or not.
And everybody has found that.
No, not a surprise?
AUDIENCE: I mean, just because they report something, doesn't
mean that's the way it is.
PROFESSOR: Ah well we'll come back to this again.
Yes.
Just because you say you're happier
doesn't mean you're happier.
We don't have a better way than that though.
We can't say, oh, you think you're happy.
But you'd be so happy if you were at Caltech.
You'd be just so happy.
I'm a brain measurer.
So I like objective measures.
I think if a person tells you they're happy,
they probably are.
There are certain moments, I know, when
people tell you that.
Well, we'll see.
Who knows?
I agree with you.
It's a concern.
So here's the thought, that motivation and goals are set
by temporal context.
At times, they're perceived as limited.
And all this will come that the older you get, the more
you focus on the positive things in the world.
And what makes you happy is to focus on positive things and
ignore the negative.
So how true might this be experimentally?
So they had students-- ah, this is really washed out--
capture these special moments, this same ad.
And this one says, "Capture the special moments." And this
one says, "Capture the unexplored world."
So if you're an information seeker, which is better? the
unexplored world or the special
moments, which is better?
The unexplored world, right?
You're a 20-year-old.
Unexplored Is awesome.
Young people prefer this ad.
Older people prefer the special moments.
And by special moments, we mean emotionally satisfying.
Right?
OK.
Here's another one.
They show you up pictures of a positive and negative
expression.
It flashes away.
And there's a dot left.
If the dot appears on the right, you push your
right-hand button.
If the dot appears on the left, you push
the left-hand button.
It's simply pushing to a dot.
But if the dot is in the place where you just saw, either a
negative or a neutral face.
And what they find is for younger people, they're about
as fast whether the dot appears where the neutral or
negative face was.
They don't really care.
For the older people, they're much faster if the dot appears
where the positive face had just been.
As if their attention was locked to the positive face.
Oh, the dot appears there.
I'm ready to go.
Locked on the positive face if the dot appears here.
You go, whoa, whoa, whoa.
You shift your attention.
And that takes extra time.
So you're locked to the positive when you see a
positive and a negative face.
Here's another one where you're doing positive and
negative car options, things that are good
or bad about a car.
This line goes up.
This line goes down.
Younger people focus more on the negative options relative
to older people who focus more on the positive options.
Here's another one.
You show pictures of happy scenes, or neutral scenes, are
negative scenes.
This is a graveyard.
Young people's memory for positive, negative, and
neutral things, they remember emotional things better.
Let's go to the older people.
Look at this line way up here.
That's memory for the positive scenes.
And here's the negative scenes.
Do you see the focus on the positivity and the sort of
lack of interest in the negative stuff?
For young people, equally interesting if it's positive
or negative.
For older people, much more interesting, and sticking in
your memory if it's positive.
And not sticking in your memory if it's negative.
So one of the big questions is, is this simply about
getting older?
And I'm going to ask you to think back, if I can, to your
last days in high school, your last days in high school.
For those last days--
and I'm sure it will vary depending on your experience
in different ways--
were you primarily interested in getting that last little
bit of information about US history or calculus?
I mean, you might have been.
That could have been the critical bit of information
that will make college work out.
Or did you have a sudden--
and it's kind of embarrassing when you're 16, 17, 18--
enhanced sense of nostalgia?
Oh, this is the last time the three of us, or the six of us,
or the eight of us, or the two of us will be together.
Then we're spreading across the world to go
to different colleges.
Nobody had that feeling?
OK.
It's kind of embarrassing when you're 18.
Because you're not supposed to say that kind of stuff.
And it will happen to you at the end the college for most
of you most of the time.
I remember senior year, it crept up on us in college.
And we started college.
Oh my gosh.
This is the last year we're together.
And it seemed very emotionally important.
So age or time.
So is it simply age?
Or is it time?
So they did experiments where they asked people, are you
focusing on adventure and content?
Or are you focusing on emotion and satisfaction?
When you're about to move from one city to another, people
waned to spend time with people they
really cared about.
And they were not interested in getting new information.
Two more tragic studies, if people are near death, and
they're asked this question, of course time with people,
not acquiring information.
But here's another one, inner-city gangs study in Los
Angeles, inner-city gangs involved in violence are much
more interested in time with people than in information.
And partly that goes with what is viewed from the outside.
Sometimes this kind of insane loyalty that inner-city gang
members have for one another is because they're so focused
given their situation on this relations with the other
people in their group compared to everything that's rational
about a safe growing up.
And, tragically, you know if you ask a member of inner-city
gangs how long they think they'll live, they often tell
you not very long.
I'm counting on not living very long.
So it's not whether you're 20, or 60, or 80.
It's how long you sense time is in front of
you, a temporal horizon.
Here's one study that I had a hand in.
We took older and younger people and put them inside an
MRI and show them positive, neutral,
and negative pictures.
Here's a couple different points.
When they said, how intense is this picture?
Look at younger people.
The positive, neutral, and the negative are really intense.
This goes down.
So the older people, as they see the pictures, experienced
by their own report, the negative pictures as being
less intense.
They're sort of downplaying the negative.
And if we asked their memory, here's younger people.
Positive, and negative things, neutral things, same for
positive and negative.
Look at older people, much more focused in memory,
retaining in memory the positive and
not so much the negative.
And if we look at their amygdala, which we know is a
structure that's essential for how emotion modulates the
formation of memory, here's young people.
Here's a positive picture.
Here's a negative picture.
Here's a neutral picture.
So emotion counts.
Positive and negative count about the same.
Look at older people.
Here's positive, and here's negative.
So this partly addresses the question for some people.
Are older people pretending they're positive?
Well, it doesn't look like that.
This is their amygdala as they're looking at it.
I don't know if their amygdala can pretend
to look at the positive.
So here's the good news for you.
What will happen as you get older, on average, is that for
whatever reason it happens-- and we don't really know why--
you will focus more and more on the positive
things in your life.
And you'll feel better for that, on average.
So that's the kind of quiet satisfaction.
Now I'm focusing on the positive.
That's the zen satisfaction.
Let's talk about fantastic satisfaction, reward system.
When you really want to do something, because it's going
to feel so wonderful, the reward system.
So let me tell you a little bit about what we understand
about that.
It involves dopamine as the critical neurotransmitter.
It starts in the ventral tegmental
area of your brainstem.
And that projects to something called the nucleus accumbens,
an inferior portion of the basal ganglia.
And this is reward central.
If you love something from opera, to chocolate, to video
games, this turns on.
Every experiment that people have ever done shows in humans
if something really turns you on, this area
really gets turned on.
What's more powerful for us than what we find deeply
emotionally rewarding?
This is that rewards system.
And the dopamine runs from there.
And look at how cells respond.
I'm going to show you an example from monkeys where we
can look at single cells.
And then brain imaging, back to people.
So here's the experiment with monkeys.
And there's a message in this that's both biologically true
and compelling about human life.
So what's biologically true in science what's compelling
about life is a story.
So here's the experiment.
The monkey sits there and gets various cues, different visual
things that tell them what's coming up.
Let's pretend this is a cue that's something wonderful is
coming up, highly desired food.
So they're recording electrically why
the animal sees this.
There's waiting for what we call the anticipation period.
And now here comes the reward.
And here's something sort of deep, I think, about reward,
and learning, and people, and things like this.
So here's the neurons firing.
This is the sum of the neurons firing in the ventral
tegmental area.
So right now they're just sitting there.
Oops, here comes the reward.
And boom, dopamine is released.
The dopaminergic cells are firing like crazy.
They're getting food they really want.
We're thrilled.
We're hungry, and we're getting something delicious.
Not much more rewarding can happen when
you're really hungry.
Now they predict the arrival with the cue that you saw, a
meaningless stimulus.
And look what happens.
When do these neurons fire?
Not for the food arriving, but for the visual signal that
predicts the food will come.
What's delicious for the brain is the anticipation of
something that's rewarding.
And this morning when I was thinking about this lecture, I
was thinking.
You might say this.
Think about experiences you've had that you've
looked forward to.
And almost the most delicious part, you might say, is the
anticipation of something delightful.
Often the event itself is more mixed and anticlimactic than
you would've thought.
Is that fair?
I think there's nothing better like I'm anticipating
something wonderful.
And the event can be wonderful.
But often it's a little more complicated.
That anticipation is like pure joy, because you're
dopaminergic system is firing freely away.
And it protests also.
So you get the visual signal that, oh, the
reward's coming up.
Here it is.
Here comes the food.
The food doesn't come.
Look at the silence.
These cells are protesting because they didn't get what
they expected to get.
So it's very compelling that the reward in you occurs not
even so much for the reward itself, but the anticipation
of the reward is where it's biologically occurring when
you can anticipate and count on it correctly.
So, in humans, it's harder to deliver-- not impossible--
food in a scanner.
So a very simple thing is done for a reward, which is
offering people money.
So in a given trial on a scanner, you might see a
meaningless cue like this.
But you learn that this box predicts that at the end of
this trial--
you do many trials--
you're going to get $1.00.
Another one might be $0.10.
Another one they might take away $1.00.
So this is like a good one to get.
I'm going to get $1 just sitting here.
I'm going to get $1.
It's not huge.
It's not the biggest reward in the world.
But it's something for just laying in the
scanner doing nothing.
And here's what happens.
Your nucleus accumbens gets activated, where dopamine
flows from the ventral tegmental area when you
anticipate a reward.
This is not when the reward comes.
This is when you're anticipating the reward.
Here's another picture.
It's most powerful for when people
anticipate a gain, a reward.
And it's less responsive when people anticipate a loss.
So it's about gains.
Then the same system projects to the inferior parts of your
frontal lobe.
So now we're moving into the neocortex.
And that part of the brain seems to respond most
powerfully if you get the reward.
So this is really interesting, a part of your brain that
responds to the anticipation, the
dopaminergic reward system.
And then another part of their brain that responds not
whether you anticipate it.
But sometimes they trick you.
They say we're going to give you $1.
And then they go, oops.
We're not giving it to you.
This part of the brain seems to register the receipt of the
reward or not.
So there's a separation of the brain between the anticipation
of the reward and the response to whether you get
the reward or not.
Older people, when they look at these kinds of similar
reward paradigms, they're less responsive to potential loss
but equally responsive to potential
gain as young adults.
So that's exactly responding to positive things and showing
less of a response to potential negative things.
So let's switch to adolescents.
We're going to focus on adolescents now mostly for the
next 10 minutes.
You just got through that.
So let's reflect back for the last couple of years.
And they make the experiments because they want to put
children into a little bit more of a vivid.
Here's pirates.
Here's not much reward.
Here's some reward.
Here's a lot of reward in the scanner.
And your children are adolescents or young adults.
And they look in the nucleus accumbens.
This is that reward region.
And look who's firing like crazy?
Adolescents, teenagers.
But they're not firing like crazy in the frontal cortex.
So this is very speculative.
These are partly just wide stories.
But one hypothesis is this.
And we're going to say in a minute more about this.
Adolescence is a really interesting period.
Because it's not only when you're deciding who you are in
the world in many ways independently.
It's also, worrisomely for parents, grandparents,
cousins, siblings, the period in life when people are most
likely to put themselves at great risk.
And one version of that is that the subcortical reward
areas are developing way faster than the cortical areas
that control and regulate your behavior.
This goes with the stereotype which is probably as unfair as
any other stereotype of the out of control teenager.
But imagine if it were true that your reward system is
very turned up.
And your cortical control system were not yet caught up
to the adult level.
Well, that would make you a little bit more likely to do
adventuresome things.
Because the reward is powerful.
And the control of your thoughts about how to approach
or reject that reward are less powerful.
So here's some things to think about.
And people worry about for adolescents.
40% of adult alcoholics report having initial alcoholism
between 15 and 19.
Between 16 and 20, both sexes are twice as likely to be in
accidents than drivers between 20 and 50, twice the
accidental rate.
Adolescents are more likely to engage in impulsive sexual
behavior and multiple partners.
Annually, three million adolescents contract a sexual
transmitted disease.
So lots of things that are risky behaviors occur with
high frequency in a demonstrable way, on average,
among adolescents.
Young kids don't drive yet.
20-year-olds are a bit more mature in their driving.
So part of this is, again, attitudinal.
Here's a question that people were asked about future
perspectives.
They were asked, I would rather save my money for a
rainy day than spend it on something fun right now.
In your 20s, a little bit.
That's growing.
You'll keep the dollar.
But the younger you are in your teenage years, the more
like who wants to wait.
Let's do it now.
So moving from something fun to something experimental,
let's put together a couple last things.
So here's a thing we did before several times in this
class, creating false memories.
And you remember the way they create false memories in the
laboratory is they pick a word they don't present to you,
like sweet.
Then they ask many students to say what words go with that
word, like sour, or candy, or sugar?
They present you this list.
And then they test you for this word
that was not presented.
And people often imagine incorrectly that they heard or
saw this word.
We've done that a couple of times.
It's a way to show illusory memory.
And the way we understand it is basically this.
Your memory, your mind, mostly thinks about the essence of
things, not the details of things.
The essence of things was everything is sweet.
The details were the specific words in the list.
So let's look at older adults versus younger adults,
80-year-olds versus 20-year-olds and exactly this
experiment.
Older adults have many more false memories.
And they perform less well.
So to a scary extend, the healthy 70-year-olds, here's
their real memories.
Here's their false memories.
It's dead even.
Here's young people having lots of false memories, but
not as many as older people, and having
more correct memories.
So older adults have more false memories, because
they're encoding the gist a lot, but
they're losing the specifics.
Does that make sense?
And you're really vulnerable to false memories.
Children, you might think, well children,
what do they know?
Children have less false memories than you do.
You would have less false memories at age five than you
would right now, which is kind of amazing.
If you didn't do the experiment, you'd imagine
children would be totally confused.
They'd get a big list of words.
Was sweet on the list?
I don't know.
Yeah, sure.
A five-year-old does better than a seven, does better than
an 11-year-old, does better than a 20-year-old.
Why?
Why does a five-year-old have less false memories under the
circumstances?
Well, we understand that to be the price of having a mind
that understands a lot of gist.
As you become older, you understand what's important,
what counts.
It's not the little details.
It's the big concepts.
So here's an example of, for example, how well people can
relate words across sentences.
And that grows from six to nine.
And that's what we want.
You don't want to read word, word, word.
You want to say, what's the point of the sentence?
That process of saying, I don't care about the detail.
I care about the concept, the gist of the concept, it's like
the chess players.
You shed the specific details to gain the
overall knowledge advantage.
But the five-year-old is not making the big picture.
They're just getting the little details.
So they're less prone to the illusory memories.
We can't see that.
But this is just showing that when it comes to organizing
memories, you see that develop across a childhood.
Last couple of things.
Because when I heard this a few years ago at a conference,
I was so surprised by these findings.
And I've been around long enough that i don't get as
surprised as often as I used to.
But it's kind of really interesting.
It's a total twist.
And you can make a judgment call about how
to interpret it.
But here's the experiments and the data.
So, again, we have this picture that everybody likes
because it fits with the stereotype, which is the
teenager out of control.
Their dopamine is going up.
And they're saying, let's do a lot of inappropriate things.
Because it will be rewarding.
I know everybody's against it.
So that's the stereotype.
And probably there's something true about that.
Literally, in the brain imaging, it
looks somewhat true.
But let's think about this for a moment.
You're going to be good at this.
If line a--
these are lines-- is longer than b, and line b is longer
than line c, is a longer than c?
Yes.
All right.
This is MIT.
Now answer this question truly.
Think about it for a moment.
Person a is a friend or person b.
So let's pretend you're person b and your friend was a.
You're also a friend with c.
Are a and c likely to be friends?
Let's think about this.
Is it mathematically transitive like this one?
No.
Let's think about it for a moment.
In your experience through life, on average, are your
friends mostly kind of going to like each other?
Kind of, not all the time, but kind of?
Yeah, probably.
Because if one person likes you, and another person likes
you, you share interests.
You share background to a certain extent, in a loose
statistical way.
It's not definitive like this.
So let's take a look at what happens when you ask you two
questions to grades one through four.
OK, these kids are just making mistakes.
And they're getting smarter.
But look at this one go up just like that.
So we can say this is a growth in logical ability.
This is a growth in your everyday sense that I hang out
with a certain kind of person.
Maybe they like football.
Maybe they like skating.
Maybe they like psychology.
but that's the group I tend to hang out with.
And, on average, if I have a friend, it's because we share
some interests, or style of being.
And if I have another friend, we probably share that too.
So more than chance, they might like each other.
So this is this idea that you can separate out what you
might call purely logical analysis of things versus a
growth of social experience, basically.
So the last three slides or so.
You remember this from a bit back, from a prior example.
We said there's a framing heuristic.
People are risk averse for gains.
But they're risk-taking for losses.
If we said here's a program.
We did this before.
If Program A is adopted, 200 people are saved.
Or here's 400 people will die out of 600.
That's the same statement.
But because this is stated as a gain, people
usually like this.
Because this is stated as a loss, people
usually don't like this.
Adults are risk averse for gains, and they're risk-taking
for losses.
If something looks like a loss, roll the dice.
If something looks like it's going to work out, go with it,
even though numerically, these are identical.
You can't see this.
I can tell you.
It's not present in
preschoolers or second graders.
Preschoolers or second graders, when you give them
these kinds of problems, they don't show the asymmetry for
losses and gains.
That's something that happens over time.
And it's not a logical one.
Logically, it should be that.
So in that weird sense, the preschooler is more logical
than you and I, more logical than you and I. Because
there's no reason to be statistically different for
losses and gains.
That's purely an attitudinal emotional perspective.
First of all, you can hear the information-seeking.
Let's check it out.
That's kind of interesting, swimming with sharks.
I can assure you 70-year-olds are not going to go, hey, that
can be kind of interesting.
They're going, no!
Terrible idea!
Don't do it!
Yeah?
AUDIENCE: Were they asked in a group collectively?
PROFESSOR: Yeah.
You see some peer influence.
Yeah.
And that doesn't happen with adolescents, right?
They do this.
They go, oh my gosh.
These are these teenagers who are going to go do all these
things, and get horrible sexual diseases, and drive
while they are impaired.
And that's just the beginning of their weekend.
Because they're not going to follow all the advice that we
gave them for years, and years, and years, and years,
at home and in school.
So here's the flip on this.
And just think about it for a moment.
It's complicated.
Swimming with sharks, the adults say, you don't have to
tell me any more.
It's a bad idea.
The gist is sharks, bad.
I don't even need to hear the rest of the story.
Adolescents start to weigh the factors.
We'd be safer in a group.
Is it dark or night outside?
How shallow is the water?
And you can say, well, it's kind of ridiculous.
But it's not totally ridiculous.
Because when we talk about danger, those are some of the
things you might start to think about.
So by this analysis, having unprotected sex.
Adults, bad, bad, bad.
OK?
I mean really bad.
Adolescents, well, let's think about this.
What's the gain?
Well, we hear that sex is highly pleasurable.
What's the loss?
All these things everybody's telling us.
What's the odds, purely statistically, that for a
single, sexual experience, you will have the pleasure of sex,
but you will end up with a terrible disease?
What's the odds for one outing?
What do you think?
Here's the complexity.
Some people argue that adolescents are actually more
accurate in their assessment of risk, not
wise in their choice.
Do you understand the point?
They're actually doing the calculations, whereas adults
just go, sharks bad.
Sexually transmitted diseases, avoid.
You're not parsing through the exact odds and circumstances,
the trade-offs between exploration and pleasure and
responsibility and safety.
You just have the gist, the line, that's it.
That's my wisdom that I've gotten.
Sharks, bad.
Sexually transmitted disease, bad.
That's it.
And these teenagers are kind of curiously thinking about
what are the factors.
And you could say, it's not the best analysis.
But you could say it's almost more rational.
Just like the older adults will make more gist errors in
memory, they will be more emotional in their
avoidance of risk.
So it's very complicated.
It's not just dopamine flushing.
It's also in the brain.
It's also something about how risk is perceived at different
ages and what information is available to you.
All right.
Thanks very much.