Neil Burgess: How your brain tells you where you are

Translator: Carme Paz Reviewer: Xusto Rodriguez

When we park in a big parking lot,

Cando aparcamos nun estacionamento grande,

how do we remember where we parked our car?

como lembramos onde deixamos o coche?

Here's the problem facing Homer.

Este é o problema que ten Homer.

And we're going to try to understand

E imos tratar de comprender

what's happening in his brain.

o que ocorre no seu cerebro.

So we'll start with the hippocampus, shown in yellow,

Comezaremos co hipocampo, en amarelo,

which is the organ of memory.

que é o órgano da memoria.

If you have damage there, like in Alzheimer's,

Se se dana, como no alzhéimer,

you can't remember things including where you parked your car.

non se lembran cousas como onde aparcamos.

It's named after Latin for "seahorse,"

É o nome en latín para 'cabaliño de mar',

which it resembles.

ao que se asemella.

And like the rest of the brain, it's made of neurons.

E como o resto do cerebro, componse de neuronas.

So the human brain

O cerebro humano

has about a hundred billion neurons in it.

ten uns cen mil millóns de neuronas.

And the neurons communicate with each other

As neuronas comunícanse entre si

by sending little pulses or spikes of electricity

con pequenos impulsos ou picos eléctricos

via connections to each other.

a través das súas conexións.

The hippocampus is formed of two sheets of cells,

O hipocampo componse de dúas capas de células

which are very densely interconnected.

densamente conectadas.

And scientists have begun to understand

Os científicos comezaron a entender

how spatial memory works

como funciona a memoria espacial

by recording from individual neurons

rastrexando neuronas individuais

in rats or mice

de ratas ou ratos

while they forage or explore an environment

ao alimentárense ou exploraren un medio

looking for food.

en busca de comida.

So we're going to imagine we're recording from a single neuron

Imaxinemos que rexistramos unha neurona individual

in the hippocampus of this rat here.

do hipocampo desta rata.

And when it fires a little spike of electricity,

Cando dispara un impulso eléctrico,

there's going to be a red dot and a click.

aparece un punto vermello e un clic.

So what we see

O que vemos é

is that this neuron knows

que esta neurona sabe

whenever the rat has gone into one particular place in its environment.

se a rata foi a un lugar específico do seu medio.

And it signals to the rest of the brain

E dálle un sinal ao resto do cerebro

by sending a little electrical spike.

enviando un pequeno impulso eléctrico.

So we could show the firing rate of that neuron

Así que podemos ver a taxa de disparos desa neurona

as a function of the animal's location.

como unha función localizadora do animal.

And if we record from lots of different neurons,

E se rastrexamos moitas neuronas diferentes,

we'll see that different neurons fire

vemos que diferentes neuronas dan sinais

when the animal goes in different parts of its environment,

cando o animal vai a sitios diferentes,

like in this square box shown here.

como nesta caixa cadrada.

So together they form a map

Todas xuntas forman un mapa

for the rest of the brain,

para o resto do cerebro,

telling the brain continually,

dicíndolle continuamente:

"Where am I now within my environment?"

"Onde estou agora no meu contorno?"

Place cells are also being recorded in humans.

As células de lugar tamén se rexistran en persoas.

So epilepsy patients sometimes need

Os pacientes de epilepsia ás veces precisan

the electrical activity in their brain monitoring.

que se vixíe a súa actividade eléctrica cerebral.

And some of these patients played a video game

Algúns pacientes xogaron a un videoxogo

where they drive around a small town.

no que conducían ao redor dunha vila.

And place cells in their hippocampi would fire, become active,

E as células de lugar do hipocampo dispararían, activaríanse,

start sending electrical impulses

comezarían a enviar impulsos eléctricos

whenever they drove through a particular location in that town.

cada vez que pasaban por un punto determinado da vila.

So how does a place cell know

Como pode saber unha célula de lugar

where the rat or person is within its environment?

onde está a rata ou a persoa dentro do seu contorno?

Well these two cells here

Pois ben, estas dúas células

show us that the boundaries of the environment

indícannos que os límites do contorno

are particularly important.

son especialmente importantes.

So the one on the top

A que está arriba

likes to fire sort of midway between the walls

dispara nalgún punto entre as paredes

of the box that their rat's in.

da caixa onde está a rata.

And when you expand the box, the firing location expands.

E se ampliamos a caixa, amplíase tamén o lugar destes disparos.

The one below likes to fire

A da parte inferior dispara

whenever there's a wall close by to the south.

cando atopa unha parede cara ao sur.

And if you put another wall inside the box,

E se pomos outra parede na caixa,

then the cell fires in both place

a célula dispara a ambos os lados

wherever there's a wall to the south

cada vez que haxa unha parede ao sur

as the animal explores around in its box.

mentres o animal explora a caixa.

So this predicts

Así que isto predí a percepción

that sensing the distances and directions of boundaries around you --

das distancias e direccións dos límites ao redor,

extended buildings and so on --

is particularly important for the hippocampus.

edificios grandes e así...,

é especialmente importante para o hipocampo.

And indeed, on the inputs to the hippocampus,

E, de feito, nas entradas do hipocampo,

cells are found which project into the hippocampus,

hai células que se proxectan no hipocampo,

which do respond exactly

que responden exactamente

to detecting boundaries or edges

á detección de límites ou bordos

at particular distances and directions

en distancias específicas e direccións

from the rat or mouse

desde onde a rata ou o rato

as it's exploring around.

explora o contorno.

So the cell on the left, you can see,

Así que a célula á esquerda, como vedes,

it fires whenever the animal gets near

dispara cando o animal se achega

to a wall or a boundary to the east,

a unha parede ou límite no leste,

whether it's the edge or the wall of a square box

sexa o bordo ou a parede dun espazo cadrado

or the circular wall of the circular box

ou a parede dun espazo circular,

or even the drop at the edge of a table, which the animals are running around.

ou mesmo o bordo dunha mesa cando o animal a percorre.

And the cell on the right there

E a célula da dereita

fires whenever there's a boundary to the south,

dispara sempre que hai un bordo ao sur,

whether it's the drop at the edge of the table or a wall

sexa o bordo dunha mesa ou unha parede

or even the gap between two tables that are pulled apart.

ou mesmo o baleiro entre dúas mesas que se separan.

So that's one way in which we think

Esa é unha forma en que pensamos

place cells determine where the animal is as it's exploring around.

que as células de lugar determinan onde está o animal mentres explora.

We can also test where we think objects are,

Podemos probar tamén onde cremos que están os obxectos,

like this goal flag, in simple environments --

como esta bandeira, en medios simples,

or indeed, where your car would be.

ou mesmo, onde deberiamos ter o coche.

So we can have people explore an environment

Pode haber xente que explore un medio

and see the location they have to remember.

e observe a posición que ten que lembrar.

And then, if we put them back in the environment,

E, se os levamos outra vez ao medio,

generally they're quite good at putting a marker down

xeralmente son bastante bos ao marcar

where they thought that flag or their car was.

onde pensaron que estaría a bandeira ou o coche.

But on some trials,

Pero nalgunhas probas,

we could change the shape and size of the environment

poderiamos cambiar a forma e o tamaño do medio

like we did with the place cell.

como fixemos coa célula de lugar.

In that case, we can see

Nese caso, podemos ver

how where they think the flag had been changes

como cambia onde pensan que estaba a bandeira,

as a function of how you change the shape and size of the environment.

en función de como cambiamos a forma e o tamaño do medio.

And what you see, for example,

Vemos, por exemplo,

if the flag was where that cross was in a small square environment,

se a bandeira estaba onda a cruz dun espazo pequeno cadrado

and then if you ask people where it was,

e lle preguntamos á xente onde estaba

but you've made the environment bigger,

pero aumentamos o espazo,

where they think the flag had been

o lugar onde crían que estaba a bandeira

stretches out in exactly the same way

amplíase exactamente da mesma maneira

that the place cell firing stretched out.

que os disparos da célula de lugar.

It's as if you remember where the flag was

É coma se lembrásedes onde estaba a bandeira

by storing the pattern of firing across all of your place cells

gardando o patrón de disparos a través das células de lugar

at that location,

nesa posición,

and then you can get back to that location

e puidésedes volver á posición

by moving around

movéndovos

so that you best match the current pattern of firing of your place cells

ata facer coincidir o padrón actual das células de lugar

with that stored pattern.

co outro padrón almacenado.

That guides you back to the location that you want to remember.

Iso guíanos de volta á posición que queremos lembrar.

But we also know where we are through movement.

Pero tamén sabemos onde estamos a través do movemento.

So if we take some outbound path --

Se collemos un camiño de saída,

perhaps we park and we wander off --

quizais aparcamos e damos unha volta,

we know because our own movements,

sabemos polos nosos movementos,

which we can integrate over this path

que podemos integrar nese camiño,

roughly what the heading direction is to go back.

cal é a dirección para volver.

And place cells also get this kind of path integration input

E as células de lugar tamén integran esa información

from a kind of cell called a grid cell.

a través dun tipo de célula chamada célula grella.

Now grid cells are found, again,

As células grella tamén se atopan

on the inputs to the hippocampus,

nas entradas ao hipocampo,

and they're a bit like place cells.

son un pouco como as células de lugar.

But now as the rat explores around,

Pero neste caso cando a rata explora,

each individual cell fires

cada célula individual dispara

in a whole array of different locations

a un rango de lugares moi diferentes

which are laid out across the environment

que están espallados polo medio

in an amazingly regular triangular grid.

nunha impresionante rede triangular.

And if you record from several grid cells --

E se rastrexades varias células grella,

shown here in different colors --

aquí en diferentes cores,

each one has a grid-like firing pattern across the environment,

cada unha ten un padrón de disparos nese medio como unha rede

and each cell's grid-like firing pattern is shifted slightly

e o padrón de disparos de cada célula rede cambia lixeiramente

relative to the other cells.

en relación coas outras células.

So the red one fires on this grid

Así que a vermella dispara nesta rede

and the green one on this one and the blue on on this one.

e a verde nesta e a azul nesta.

So together, it's as if the rat

E xuntas, é coma se a rata

can put a virtual grid of firing locations

fixese unha rede virtual de posicións de disparos

across its environment --

por todo o medio,

a bit like the latitude and longitude lines that you'd find on a map,

un pouco como as liñas de latitude e lonxitude que hai nun mapa

but using triangles.

pero con triángulos.

And as it moves around,

E ao moverse,

the electrical activity can pass

a actividade eléctrica pode pasar

from one of these cells to the next cell

desde unha destas células á próxima

to keep track of where it is,

para seguir a pista de onde está,

so that it can use its own movements

para que poida usar os propios movementos

to know where it is in its environment.

e saber onde está no contorno.

Do people have grid cells?

A xente ten células grella?

Well because all of the grid-like firing patterns

Ben, que todos os padróns que disparan en rede

have the same axes of symmetry,

teñan os mesmos eixes de simetrías,

the same orientations of grid, shown in orange here,

a mesma orientación da rede, en laranxa aquí,

it means that the net activity

quere dicir que a actividade

of all of the grid cells in a particular part of the brain

de todas as células grella nun lugar particular do cerebro

should change

debería cambiar

according to whether we're running along these six directions

segundo esteamos correndo nestas seis direccións

or running along one of the six directions in between.

ou nunha das seis direccións intermedias.

So we can put people in an MRI scanner

Podemos poñer xente nun escáner IRM

and have them do a little video game

e darlle un pequeno videoxogo

like the one I showed you

como o que vos amosei

and look for this signal.

e buscar este sinal.

And indeed, you do see it in the human entorhinal cortex,

E vedes no córtex entorrinal humano,

which is the same part of the brain that you see grid cells in rats.

que está na mesma parte do cerebro que as células grella das ratas.

So back to Homer.

Así que volvendo a Homer.

He's probably remembering where his car was

Estará lembrando onde puxo o coche

in terms of the distances and directions

en termos de distancias e direccións

to extended buildings and boundaries

cara a edificios extensos e límites

around the location where he parked.

ao redor da posición onde aparcou.

And that would be represented

E iso estará representado

by the firing of boundary-detecting cells.

polos disparos de células detectoras de límites.

He's also remembering the path he took out of the car park,

Tamén estará lembrando o camiño que colleu fóra do aparcamento,

which would be represented in the firing of grid cells.

que estará representado nos disparos de células grella.

Now both of these kinds of cells

Ambos os tipos de células

can make the place cells fire.

poden facer disparar as células.

And he can return to the location where he parked

E el pode volver ao lugar onde aparcou

by moving so as to find where it is

movéndose para atopalo

that best matches the firing pattern

ata que encaixe o padrón de disparos

of the place cells in his brain currently

das células de lugar

with the stored pattern where he parked his car.

co padrón almacenado de onde aparcou o seu coche.

And that guides him back to that location

E iso guíao de volta á posición

irrespective of visual cues

independentemente das pistas visuais

like whether his car's actually there.

coma se o seu coche estivese alí.

Maybe it's been towed.

Pode que llo levara o guindastre.

But he knows where it was, so he knows to go and get it.

Pero el sabe onde estaba, así que sabe onde ir e collelo.

So beyond spatial memory,

Máis alá da memoria espacial,

if we look for this grid-like firing pattern

se buscamos este padrón rede

throughout the whole brain,

a través de todo o cerebro,

we see it in a whole series of locations

vémolo nunha serie de posicións

which are always active

que están sempre activas

when we do all kinds of autobiographical memory tasks,

ao facermos tarefas de memoria autobiográfica,

like remembering the last time you went to a wedding, for example.

como lembrar a última vez que fomos a unha voda.

So it may be that the neural mechanisms

Pode que os mecanismos neuronais

for representing the space around us

para representar o espazo ao noso redor

are also used for generating visual imagery

se usen tamén para xerar imaxinaría visual,

so that we can recreate the spatial scene, at least,

para que poidamos recrear a escena espacial, polo menos,

of the events that have happened to us when we want to imagine them.

dos eventos que nos ocorreron cando os imaxinamos.

So if this was happening,

Se isto ocorrese,

your memories could start by place cells activating each other

as vosas memorias comezarían activando entre si as células de lugar

via these dense interconnections

a través desas densas conexións

and then reactivating boundary cells

e reactivando células límite

to create the spatial structure

para crear a estrutura espacial

of the scene around your viewpoint.

ao redor da vosa perspectiva.

And grid cells could move this viewpoint through that space.

E as células grella poderían mover a perspectiva no espazo.

Another kind of cell, head direction cells,

Outro tipo de célula, as de dirección da cabeza,

which I didn't mention yet,

que aínda non mencionei,

they fire like a compass according to which way you're facing.

disparan como un compás de acordo co camiño que seguides.

They could define the viewing direction

Poden definir a dirección da vista

from which you want to generate an image for your visual imagery,

desde onde queredes xerar unha imaxe para a vosa imaxinaría visual,

so you can imagine what happened when you were at this wedding, for example.

así que podedes imaxinar o que ocorreu nesa voda, por exemplo.

So this is just one example

Isto é só un exemplo

of a new era really

dunha nova era

in cognitive neuroscience

da neurociencia cognitiva,

where we're beginning to understand

cando comezamos a entender

psychological processes

procesos psicolóxicos,

like how you remember or imagine or even think

como o xeito en que lembramos ou imaxinamos ou mesmo pensamos

in terms of the actions

en termos de accións

of the billions of individual neurons that make up our brains.

dos centos de miles de neuronas individuais que forman o cerebro.

Thank you very much.

Moitas grazas.

(Applause)

(Aplausos)