Sarah-Jayne Blakemore: The mysterious workings of the adolescent brain

Translator: Joseph Geni Reviewer: Morton Bast

Translator: Montse Corral Reviewer: Serv. de Norm. Lingüística U. de Santiago de Compostela

Fifteen years ago, it was widely assumed

Hai 15 anos, pensábase que

that the vast majority of brain development

a maior parte do desenvolvemento cerebral

takes place in the first few years of life.

tiña lugar nos primeiros anos de vida.

Back then, 15 years ago, we didn't have the ability

Daquela, hai 15 anos, non eramos quen

to look inside the living human brain

de mirar dentro do cerebro humano vivo

and track development across the lifespan.

e observar os seus cambios ao longo da vida.

In the past decade or so, mainly due to advances

Na última década, grazas aos avances

in brain imaging technology

nas técnicas de neuroimaxe cerebral

such as magnetic resonance imaging, or MRI,

como a resonancia magnética ou RM,

neuroscientists have started to look inside the living

os neurocientíficos comezaron a explorar en vivo

human brain of all ages, and to track changes

cerebros de todas as idades e a seguir

in brain structure and brain function,

os cambios na estrutura e na función cerebral.

so we use structural MRI if you'd like to take a snapshot,

Cando queremos facer unha foto de alta resolución

a photograph, at really high resolution of the inside

do cerebro humano vivo, usamos a RM

of the living human brain, and we can ask questions like,

e así podemos facer preguntas como:

how much gray matter does the brain contain,

canta materia gris contén o cerebro

and how does that change with age?

e como cambia coa idade?

And we also use functional MRI, called fMRI,

Tamén usamos a RM funcional ou RMf,

to take a video, a movie, of brain activity

para gravar un vídeo, unha película da actividade cerebral

when participants are taking part in some kind of task

cando alguén está a facer algunha tarefa

like thinking or feeling or perceiving something.

como pensar ou sentir ou percibir algo.

So many labs around the world are involved in this kind

Moitos laboratorios do mundo están a facer

of research, and we now have a really rich

este tipo de investigación, así que temos unha imaxe

and detailed picture of how the living human brain develops,

moi completa de como se desenvolve o cerebro humano

and this picture has radically changed the way

e esa imaxe cambiou moito

we think about human brain development

o noso xeito de pensar sobre o desenvolvemento

by revealing that it's not all over in early childhood,

ao mostrar que non todo remata na infancia,

and instead, the brain continues to develop

senón que continúa ao longo da adolescencia

right throughout adolescence and into the '20s and '30s.

ata ben entrados os 20 - 30 anos.

So adolescence is defined as the period of life that starts

A adolescencia é a etapa que comeza cos cambios

with the biological, hormonal, physical changes of puberty

biolóxicos, hormonais e físicos da puberdade e

and ends at the age at which an individual attains

finaliza á idade na que a persoa

a stable, independent role in society.

acada un posto estable e independente na sociedade.

(Laughter)

(Risas)

It can go on a long time. (Laughter)

Pode alongarse moito tempo. (Risas)

One of the brain regions that changes most dramatically

Unha das rexións que máis cambia durante

during adolescence is called prefrontal cortex.

a adolescencia é o córtex prefrontal.

So this is a model of the human brain,

Aquí teñen unha maqueta do cerebro humano,

and this is prefrontal cortex, right at the front.

e aquí, diante, está o córtex prefrontal.

Prefrontal cortex is an interesting brain area.

O córtex prefrontal é moi interesante.

It's proportionally much bigger in humans than

Proporcionalmente é meirande nos humanos que en calquera outra especie,

in any other species, and it's involved in a whole range of

e está implicado nunha morea de funcións cognitivas de alto nivel,

high level cognitive functions, things like decision-making,

como a toma de decisións, a planificación,

planning, planning what you're going to do tomorrow

planear que imos facer mañá ou a próxima semana

or next week or next year, inhibiting

ou o próximo ano, inhibir condutas inapropiadas,

inappropriate behavior, so stopping yourself saying

como frearnos antes de dicir unha grosería

something really rude or doing something really stupid.

ou facer unha estupidez.

Está tamén implicado na interacción social,

It's also involved in social interaction,

understanding other people, and self-awareness.

en comprender aos outros, e na autoconciencia.

So MRI studies looking at the development of this region

Os estudos con RM teñen amosado que

have shown that it really undergoes dramatic development

esta rexión sofre un cambio notable

during the period of adolescence.

durante a adolescencia.

So if you look at gray matter volume, for example,

Se observamos nesta figura os cambios

gray matter volume across age from age four to 22 years

no volume de materia gris, entre os 4 e os 22 anos,

increases during childhood, which is what you can see

vese que aumenta durante a infancia,

on this graph. It peaks in early adolescence.

e chega ao seu pico na adolescencia.

The arrows indicate peak gray matter volume

As frechas sinalan o pico de volume de materia gris

in prefrontal cortex. You can see that that peak happens

no córtex prefrontal. Os nenos acadan o pico

a couple of years later in boys relative to girls,

un par de anos máis tarde cás nenas,

and that's probably because boys go through puberty

probablemente porque, de media, acadan

a couple of years later than girls on average,

a puberdade un par de anos máis tarde ca elas.

and then during adolescence, there's a significant decline

E durante a adolescencia hai un declive significativo

in gray matter volume in prefrontal cortex.

no volume de materia gris no córtex prefrontal.

Now that might sound bad, but actually this is

Podería parecer algo malo, pero en realidade

a really important developmental process, because

trátase dun proceso moi importante do desenvolvemento,

gray matter contains cell bodies and connections

porque a materia gris contén corpos celulares

between cells, the synapses, and this decline

e conexións entre células, as sinapses, e este declive

in gray matter volume during prefrontal cortex

no volume de materia gris no córtex prefrontal

is thought to correspond to synaptic pruning,

responde á poda sináptica,

the elimination of unwanted synapses.

á eliminación das sinapses irrelevantes.

This is a really important process. It's partly dependent

Este é un proceso moi importante.

on the environment that the animal or the human is in,

Depende en parte do ambiente no que un se desenvolve.

and the synapses that are being used are strengthened,

As sinapses que están a usarse vense

and synapses that aren't being used

fortalecidas e as que non se usan,

in that particular environment are pruned away.

nese ambiente particular, pódanse.

You can think of it a bit like pruning a rosebush.

Poden velo como a poda dunha roseira.

You prune away the weaker branches so that

Pódanse as ramas febles para que

the remaining, important branches, can grow stronger,

as que quedan, as importantes, crezan robustas e

and this process, which effectively fine-tunes brain tissue

este proceso, que axusta eficazmente o tecido cerebral

according to the species-specific environment,

ao ambiente específico de cada especie,

is happening in prefrontal cortex and in other brain regions

ocorre no córtex prefrontal e noutras rexións cerebrais

during the period of human adolescence.

durante a etapa da adolescencia.

So a second line of inquiry that we use to track changes

Unha segunda liña de investigación para explorar

in the adolescent brain is using functional MRI

os cambios no cerebro adolescente é usar a RM funcional

to look at changes in brain activity across age.

para ver como cambia a actividade cerebral coa idade.

So I'll just give you an example from my lab.

Dareilles un exemplo do meu laboratorio.

So in my lab, we're interested in the social brain, that is

Estamos interesados no cerebro social,

the network of brain regions that we use to understand

na rede de rexións cerebrais que usamos

other people and to interact with other people.

para comprender aos outros e interactuar con eles.

So I like to show a photograph of a soccer game

Voulles mostrar unha foto dun partido de fútbol

to illustrate two aspects of how your social brains work.

para ilustrar dous aspectos do modo en que traballa o cerebro social.

So this is a soccer game. (Laughter)

Este é o partido de fútbol. (Risas)

Michael Owen has just missed a goal, and he's lying

Michael Owen acaba de fallar un gol

on the ground, and the first aspect of the social brain

e está tirado no céspede. E o primeiro aspecto

that this picture really nicely illustrates is how automatic

que ilustra tan ben esta foto é o automáticas

and instinctive social emotional responses are,

e instintivas que son as respostas emocionais sociais,

so within a split second of Michael Owen missing this goal,

de xeito que unha décima de segundo despois de que fallara o gol,

everyone is doing the same thing with their arms

todo o mundo está a facer o mesmo xesto cos brazos

and the same thing with their face, even Michael Owen

e coa cara, mesmo Michael Owen, tirado no céspede,

as he slides along the grass, is doing the same thing

fai o mesmo cos brazos

with his arms, and presumably has a similar

e probablemente ten a mesma expresión facial.

facial expression, and the only people who don't

As únicas persoas que non o fan

are the guys in yellow at the back — (Laughs) —

son os mozos de amarelo do fondo. (Risas)

and I think they're on the wrong end of the stadium,

Creo que se equivocaron de bancada,

and they're doing another social emotional response

e están a mostrar outra resposta emocional

that we all instantly recognize, and that's the second aspect

que todos recoñecemos ao momento.

of the social brain that this picture really nicely illustrates,

Este é o segundo aspecto do cerebro social que ilustra tan ben esta foto,

how good we are at reading other people's behavior,

o bos que somos lendo a conduta dos demais,

their actions, their gestures, their facial expressions,

as súas accións, xestos, expresións faciais,

in terms of their underlying emotions and mental states.

en termos dos estados mentais e as emocións subxacentes.

So you don't have to ask any of these guys.

Non precisamos falar con eses mozos.

You have a pretty good idea of what they're feeling

Facémonos unha idea do que están a sentir

and thinking at this precise moment in time.

e a pensar nese momento.

E niso é no que estamos interesados no meu laboratorio.

So that's what we're interested in looking at in my lab.

So in my lab, we bring adolescents and adults into the lab

Traemos a adolescentes e a adultos

to have a brain scan, we give them some kind of task

para facerlles un escáner, pedímoslles que fagan

that involves thinking about other people, their minds,

algunha tarefa na que teñan que pensar

their mental states, their emotions, and one of the findings

sobre os estados mentais e as emocións doutras persoas,

that we've found several times now, as have other labs

e un dos achados que atopamos repetidamente,

around the world, is part of the prefrontal cortex called

como noutros laboratorios do mundo,

medial prefrontal cortex, which is shown in blue on the slide,

ten que ver co córtex prefrontal medial,

and it's right in the middle of prefrontal cortex

en azul na diapositiva, unha rexión situada

in the midline of your head.

xusto na liña media da cabeza.

This region is more active in adolescents when they make

Esta rexión está máis activa nos adolescentes que nos adultos

these social decisions and think about other people

cando toman decisións sociais e pensan sobre outros.

than it is in adults, and this is actually a meta-analysis

Trátase do resultado dunha metaanálise

of nine different studies in this area from labs around

de 9 estudos diferentes de laboratorios

the world, and they all show the same thing, that activity

de todo o mundo, e todos mostran o mesmo,

in this medial prefrontal cortex area decreases

esa actividade no córtex prefrontal medial

during the period of adolescence.

diminúe durante a adolescencia.

And we think that might be because adolescents and adults

Pensamos que responde a que adolescentes e adultos

use a different mental approach, a different

usan unha estratexia cognitiva distinta

cognitive strategy, to make social decisions,

para tomar decisións sociais e

and one way of looking at that is to do behavioral studies

para comprobalo traemos á xente ao noso laboratorio

whereby we bring people into the lab and we give them

e pedímoslles unha tarefa condutual.

some kind of behavioral task, and I'll just give you

Voulles dar un exemplo

another example of the kind of task that we use in my lab.

do tipo de tarefa que usamos no meu laboratorio.

So imagine that you're the participant in one of our

Imaxinen que participan nun dos nosos experimentos.

experiments. You come into the lab,

Veñen ao laboratorio

you see this computerized task.

e ven esta tarefa no ordenador.

In this task, you see a set of shelves.

Poden ver que hai uns estantes.

Now, there are objects on these shelves, on some of them,

Nalgúns deles hai obxectos,

and you'll notice there's a guy standing behind the set

e fíxense que hai un tipo detrás dos estantes,

of shelves, and there are some objects that he can't see.

e hai obxectos que non pode ver.

They're occluded, from his point of view, with a kind of

Están ocultos, dende a súa perspectiva,

gray piece of wood.

cunha peza de madeira gris.

This is the same set of shelves from his point of view.

Estes son os mesmos estantes dende a súa perspectiva.

Notice that there are only some objects that he can see,

Fíxense que el só pode ver algúns obxectos,

whereas there are many more objects that you can see.

e que vostedes poden ver moitos máis.

Now your task is to move objects around.

O que teñen que facer é mover os obxectos.

The director, standing behind the set of shelves,

O director, situado detrás dos estantes,

is going to direct you to move objects around,

diralles a onde movelos,

but remember, he's not going to ask you to move objects

pero lembren: non lles vai pedir que movan

that he can't see. This introduces a really interesting

obxectos que el non pode ver.

condition whereby there's a kind of conflict

Isto é interesante, porque hai un certo conflito

between your perspective and the director's perspective.

entre a súa perspectiva e a do director.

So imagine he tells you to move the top truck left.

Imaxinen que lles di que movan o camión de arriba cara á esquerda.

There are three trucks there. You're going to instinctively

Hai tres camións. Instintivamente irán polo branco,

go for the white truck, because that's the top truck

porque é o que está máis arriba

from your perspective, but then you have to remember,

dende a súa perspectiva, pero entón lembran

"Oh, he can't see that truck, so he must mean

"Ah, el non pode ver ese camión,

me to move the blue truck," which is the top truck

así que ten que referirse ao azul",

from his perspective. Now believe it or not,

o máis alto dende a perspectiva del.

normal, healthy, intelligent adults like you make errors

Créanme ou non, adultos sans e intelixentes coma vostedes

about 50 percent of the time on that kind of trial.

cometen erros un 50% das veces nestes ensaios.

They move the white truck instead of the blue truck.

Moven o camión branco no canto do azul.

So we give this kind of task to adolescents and adults,

Pasámoslles a tarefa a mozos e adultos

and we also have a control condition

e incluímos unha condición de control

where there's no director and instead we give people a rule.

na que en vez do director dabámoslles unha regra.

We tell them, okay, we're going to do exactly the same thing

Dixémoslles: imos facer o mesmo

but this time there's no director. Instead you've got to

pero desta volta sen director.

ignore objects with the dark gray background.

Esta vez teñen que ignorar os obxectos co fondo gris.

You'll see that this is exactly the same condition, only

Fíxense que é exactamente o mesmo,

in the no-director condition they just have to remember

só que agora teñen que acordarse

to apply this somewhat arbitrary rule, whereas

de aplicar esta regra un tanto arbitraria,

in the director condition, they have to remember

mentres que antes tiñan que recordar

to take into account the director's perspective

ter en conta a perspectiva do director

in order to guide their ongoing behavior.

para guiar a súa resposta.

Okay, so if I just show you the percentage errors

Voulles mostrar a porcentaxe de erros

in a large developmental study we did,

no estudo de desenvolvemento que fixemos,

this is in a study ranging from age seven to adulthood,

que abarcaba dos 7 anos á idade adulta,

and what you're going to see is the percentage errors

e van ver a porcentaxe de erros

in the adult group in both conditions,

dos adultos en ambas as dúas condicións,

so the gray is the director condition, and you see

en gris a do director, e verán que

that our intelligent adults are making errors about 50 percent

os adultos intelixentes cometen erros un 50% das veces

of the time, whereas they make far fewer errors

e que cometen menos erros

when there's no director present, when they just have

cando o director non está presente,

to remember that rule of ignoring the gray background.

cando teñen que recordar a regra de ignorar o fondo gris.

Developmentally, these two conditions develop

Evolutivamente, estas dúas condicións

in exactly the same way. Between late childhood

desenvólvense igual. Hai unha mellora

and mid-adolescence, there's an improvement,

entre a infancia e a adolescencia.

in other words a reduction of errors, in both of these trials,

Noutras palabras, hai unha redución dos

erros nas dúas condicións.

in both of these conditions.

But it's when you compare the last two groups,

Pero é cando comparamos os dous últimos grupos,

the mid-adolescent group and the adult group

adolescentes e adultos,

where things get really interesting, because there, there is

cando as cousas se poñen interesantes,

no continued improvement in the no-director condition.

porque aí non continúa a mellora na condición sen director.

In other words, everything you need to do in order to

Noutras palabras, o necesario

remember the rule and apply it seems to be fully developed

para recordar e aplicar a regra

by mid-adolescence, whereas in contrast,

xa está desenvolto na adolescencia;

if you look at the last two gray bars, there's still

mentres que, se observan as dúas últimas barras grises,

a significant improvement in the director condition

verán que aínda hai unha mellora significativa

na condición director entre a adolescencia e a idade adulta.

between mid-adolescence and adulthood, and what

this means is that the ability to take into account someone

Isto significa que a capacidade para ter en conta

else's perspective in order to guide ongoing behavior,

a perspectiva dos outros para guiar a nosa conduta,

which is something, by the way, that we do in everyday life all

algo que temos que facer todos os días a todas horas,

the time, is still developing in mid-to-late adolescence.

está aínda desenvolvéndose na adolescencia.

So if you have a teenage son or a daughter and you

Ou sexa que se teñen un fillo adolescente

sometimes think they have problems taking other people's

e algunhas veces pensan que ten problemas para poñerse no lugar dos outros,

perspectives, you're right. They do. And this is why.

están no certo. Téñenos. E este é o motivo.

So we sometimes laugh about teenagers.

Ás veces rímonos dos adolescentes.

They're parodied, sometimes even demonized in the media

Mesmo os medios

for their kind of typical teenage behavior. They take risks,

critican as súas condutas típicas.

they're sometimes moody, they're very self-conscious.

Son arriscados, malhumorados, moi vergonzosos.

I have a really nice anecdote from a friend of mine

Teño unha anécdota moi divertida dun amigo

who said that the thing he noticed most

que contaba que o cambio máis patente

about his teenage daughters before and after puberty

das súas fillas adolescentes na puberdade

foi o grao de vergoña diante del. Dicía:

was their level of embarrassment in front of him.

So, he said, "Before puberty, if my two daughters

"Antes da puberdade, se as miñas fillas

estaban a amolarme nunha tenda, dicíalles

were messing around in a shop, I'd say, 'Hey,

'veña, parade e cántovos a vosa canción favorita'

stop messing around and I'll sing your favorite song,'

and instantly they'd stop messing around and he'd sing

e paraban ao momento e cantáballes a canción".

their favorite song. After puberty, that became the threat.

Despois da puberdade, iso tornouse nunha ameaza.

(Laughter)

(Risas)

The very notion of their dad singing in public

A simple idea do seu pai cantando en público

was enough to make them behave.

era suficiente para facer que se comportaran.

So people often ask,

A miúdo a xente pregunta:

"Well, is adolescence a kind of recent phenomenon?

"A adolescencia é cousa de agora?

Is it something we've invented recently in the West?"

Algo inventado en Occidente?"

And actually, the answer is probably not. There are lots

Francamente, creo que a resposta é non.

of descriptions of adolescence in history that sound

Ao longo da historia hai descricións da adolescencia

very similar to the descriptions we use today.

moi parecidas ás que usamos hoxe en día.

So there's a famous quote by Shakespeare from "The Winter's Tale"

Nunha famosa cita de "Conto de Inverno", Shakespeare

where he describes adolescence as follows:

describe así a adolescencia:

"I would there were no age between ten and

"Quixera que non mediara tempo entre os 10 e os 23 anos,

three-and-twenty, or that youth would sleep out the rest;

ou que a xuventude pasara durmindo tranquilamente;

for there is nothing in the between but getting wenches

porque non hai nada no ínterim salvo

with child, wronging the ancientry, stealing, fighting." (Laughter)

preñar mozas, aldraxar anciáns, roubar, loitar". (Risas)

He then goes on to say, "Having said that, would any

E continúa dicindo: "Dito isto, quen senón

but these boiled brains of nineteen and two-and-twenty

esas cabezas loucas de 19 e 22 anos

hunt in this weather?" (Laughter)

sairía cazar con este tempo?" (Risas)

So almost 400 years ago, Shakespeare was portraying

Ou sexa que hai 400 anos, Shakespeare

adolescents in a very similar light to the light that we

retratou aos adolescentes da mesma maneira

portray them in today, but today we try to understand

que se fai hoxe, pero aínda estamos

their behavior in terms of the underlying changes

a tentar comprender a súa conduta

that are going on in their brain.

en termos dos cambios cerebrais subxacentes.

So for example, take risk-taking. We know that adolescents

Por exemplo, as condutas de risco.

have a tendency to take risks. They do.

Sabemos da súa tendencia a arriscarse. Fano.

They take more risks than children or adults,

Corren máis riscos que os nenos ou os adultos,

and they are particularly prone to taking risks

e son particularmente proclives

when they're with their friends. There's an important drive

a asumir riscos cando están cos amigos.

to become independent from one's parents

Hai un forte pulo para independizarse dos pais

and to impress one's friends in adolescence.

e impresionar aos amigos na adolescencia.

But now we try to understand that in terms of

Agora tratamos de comprendelo en termos

the development of a part of their brain called the limbic system,

do desenvolvemento dunha parte do cerebro,

so I'm going to show you the limbic system in red

o sistema límbico. Poden velo en vermello

in the slide behind me, and also on this brain.

na diapositiva detrás de min e neste cerebro.

So the limbic system is right deep inside the brain,

O sistema límbico está na profundidade

and it's involved in things like emotion processing

do cerebro e está implicado no procesamento das emocións

and reward processing. It gives you the rewarding feeling

e da recompensa. Dános esa sensación

out of doing fun things, including taking risks.

gratificante do divertido, do risco.

It gives you the kick out of taking risks.

Dáche ese subidón ao correr un risco.

And this region, the regions within the limbic system,

Sabemos que esta rexión do sistema límbico

have been found to be hypersensitive to the rewarding

é hipersensible á sensación gratificante

feeling of risk-taking in adolescents compared with adults,

de arriscarse nos adolescentes fronte aos adultos,

and at the very same time, the prefrontal cortex,

e ao mesmo tempo, o córtex prefrontal,

which you can see in blue in the slide here,

en azul na diapositiva, que nos impide

which stops us taking excessive risks,

correr riscos excesivos, está aínda

is still very much in development in adolescents.

en desenvolvemento na adolescencia.

So brain research has shown that the adolescent brain

Así que vemos que o cerebro adolescente

undergoes really quite profound development,

experimenta un gran desenvolvemento,

and this has implications for education, for rehabilitation,

e isto ten implicacións para a educación, a rehabilitación

and intervention. The environment, including teaching,

e a intervención. O ambiente, escola incluída,

can and does shape the developing adolescent brain,

pode e dá forma ao cerebro adolescente.

and yet it's only relatively recently that we have been

Con todo, a ensinanza obrigatoria durante a adolescencia

routinely educating teenagers in the West.

é relativamente recente en Occidente.

All four of my grandparents, for example, left school

Os meus catro avós, por exemplo,

in their early adolescence. They had no choice.

deixaron a escola moi novos. Non tiñan elección.

And that's still the case for many, many teenagers

E isto segue sendo así para moitos adolescentes

around the world today. Forty percent of teenagers

de todo o mundo. O 40% deles

don't have access to secondary school education.

non teñen acceso á ensinanza secundaria.

And yet, this is a period of life where the brain is

Porén, este é un período da vida

particularly adaptable and malleable.

no que o cerebro é particularmente adaptable e maleable.

It's a fantastic opportunity for learning and creativity.

É unha oportunidade fantástica para a aprendizaxe e a creatividade.

So what's sometimes seen as the problem

Ou sexa que o que ás veces se ve como

with adolescents — heightened risk-taking, poor impulse

o problema da adolescencia --condutas de risco,

control, self-consciousness — shouldn't be stigmatized.

escaso control de impulsos, vergoña-- non debería estigmatizarse.

It actually reflects changes in the brain that provide

Reflicte cambios cerebrais que proporcionan

an excellent opportunity for education

unha grande oportunidade para a educación

and social development. Thank you. (Applause)

e o desenvolvemento social. Grazas.

(Applause)

(Aplausos)