When we park in a big parking lot, how do we remember where we parked our car? Here's the problem facing Homer. And we're going to try to understand what's happening in his brain.
Cando aparcamos nun estacionamento grande, como lembramos onde deixamos o coche? Este é o problema que ten Homer. E imos tratar de comprender o que ocorre no seu cerebro.
So we'll start with the hippocampus, shown in yellow, which is the organ of memory. If you have damage there, like in Alzheimer's, you can't remember things including where you parked your car. It's named after Latin for "seahorse," which it resembles. And like the rest of the brain, it's made of neurons.
Comezaremos co hipocampo, en amarelo, que é o órgano da memoria. Se se dana, como no alzhéimer, non se lembran cousas como onde aparcamos. É o nome en latín para 'cabaliño de mar', ao que se asemella. E como o resto do cerebro, componse de neuronas.
So the human brain has about a hundred billion neurons in it. And the neurons communicate with each other by sending little pulses or spikes of electricity via connections to each other. The hippocampus is formed of two sheets of cells, which are very densely interconnected. And scientists have begun to understand how spatial memory works by recording from individual neurons in rats or mice while they forage or explore an environment looking for food.
O cerebro humano ten uns cen mil millóns de neuronas. As neuronas comunícanse entre si con pequenos impulsos ou picos eléctricos a través das súas conexións. O hipocampo componse de dúas capas de células densamente conectadas. Os científicos comezaron a entender como funciona a memoria espacial rastrexando neuronas individuais de ratas ou ratos ao alimentárense ou exploraren un medio en busca de comida.
So we're going to imagine we're recording from a single neuron in the hippocampus of this rat here. And when it fires a little spike of electricity, there's going to be a red dot and a click. So what we see is that this neuron knows whenever the rat has gone into one particular place in its environment. And it signals to the rest of the brain by sending a little electrical spike. So we could show the firing rate of that neuron as a function of the animal's location. And if we record from lots of different neurons, we'll see that different neurons fire when the animal goes in different parts of its environment, like in this square box shown here. So together they form a map for the rest of the brain, telling the brain continually, "Where am I now within my environment?"
Imaxinemos que rexistramos unha neurona individual do hipocampo desta rata. Cando dispara un impulso eléctrico, aparece un punto vermello e un clic. O que vemos é que esta neurona sabe se a rata foi a un lugar específico do seu medio. E dálle un sinal ao resto do cerebro enviando un pequeno impulso eléctrico. Así que podemos ver a taxa de disparos desa neurona como unha función localizadora do animal. E se rastrexamos moitas neuronas diferentes, vemos que diferentes neuronas dan sinais cando o animal vai a sitios diferentes, como nesta caixa cadrada. Todas xuntas forman un mapa para o resto do cerebro, dicíndolle continuamente: "Onde estou agora no meu contorno?"
Place cells are also being recorded in humans. So epilepsy patients sometimes need the electrical activity in their brain monitoring. And some of these patients played a video game where they drive around a small town. And place cells in their hippocampi would fire, become active, start sending electrical impulses whenever they drove through a particular location in that town.
As células de lugar tamén se rexistran en persoas. Os pacientes de epilepsia ás veces precisan que se vixíe a súa actividade eléctrica cerebral. Algúns pacientes xogaron a un videoxogo no que conducían ao redor dunha vila. E as células de lugar do hipocampo dispararían, activaríanse, comezarían a enviar impulsos eléctricos cada vez que pasaban por un punto determinado da vila.
So how does a place cell know where the rat or person is within its environment? Well these two cells here show us that the boundaries of the environment are particularly important. So the one on the top likes to fire sort of midway between the walls of the box that their rat's in. And when you expand the box, the firing location expands. The one below likes to fire whenever there's a wall close by to the south. And if you put another wall inside the box, then the cell fires in both place wherever there's a wall to the south as the animal explores around in its box. So this predicts that sensing the distances and directions of boundaries around you -- extended buildings and so on -- is particularly important for the hippocampus. And indeed, on the inputs to the hippocampus, cells are found which project into the hippocampus, which do respond exactly to detecting boundaries or edges at particular distances and directions from the rat or mouse as it's exploring around.
Como pode saber unha célula de lugar onde está a rata ou a persoa dentro do seu contorno? Pois ben, estas dúas células indícannos que os límites do contorno son especialmente importantes. A que está arriba dispara nalgún punto entre as paredes da caixa onde está a rata. E se ampliamos a caixa, amplíase tamén o lugar destes disparos. A da parte inferior dispara cando atopa unha parede cara ao sur. E se pomos outra parede na caixa, a célula dispara a ambos os lados cada vez que haxa unha parede ao sur mentres o animal explora a caixa. Así que isto predí a percepción das distancias e direccións dos límites ao redor, edificios grandes e así..., é especialmente importante para o hipocampo. E, de feito, nas entradas do hipocampo, hai células que se proxectan no hipocampo, que responden exactamente á detección de límites ou bordos en distancias específicas e direccións desde onde a rata ou o rato explora o contorno.
So the cell on the left, you can see, it fires whenever the animal gets near to a wall or a boundary to the east, whether it's the edge or the wall of a square box or the circular wall of the circular box or even the drop at the edge of a table, which the animals are running around. And the cell on the right there fires whenever there's a boundary to the south, whether it's the drop at the edge of the table or a wall or even the gap between two tables that are pulled apart. So that's one way in which we think place cells determine where the animal is as it's exploring around.
Así que a célula á esquerda, como vedes, dispara cando o animal se achega a unha parede ou límite no leste, sexa o bordo ou a parede dun espazo cadrado ou a parede dun espazo circular, ou mesmo o bordo dunha mesa cando o animal a percorre. E a célula da dereita dispara sempre que hai un bordo ao sur, sexa o bordo dunha mesa ou unha parede ou mesmo o baleiro entre dúas mesas que se separan. Esa é unha forma en que pensamos que as células de lugar determinan onde está o animal mentres explora.
We can also test where we think objects are, like this goal flag, in simple environments -- or indeed, where your car would be. So we can have people explore an environment and see the location they have to remember. And then, if we put them back in the environment, generally they're quite good at putting a marker down where they thought that flag or their car was. But on some trials, we could change the shape and size of the environment like we did with the place cell.
Podemos probar tamén onde cremos que están os obxectos, como esta bandeira, en medios simples, ou mesmo, onde deberiamos ter o coche. Pode haber xente que explore un medio e observe a posición que ten que lembrar. E, se os levamos outra vez ao medio, xeralmente son bastante bos ao marcar onde pensaron que estaría a bandeira ou o coche. Pero nalgunhas probas, poderiamos cambiar a forma e o tamaño do medio como fixemos coa célula de lugar.
In that case, we can see how where they think the flag had been changes as a function of how you change the shape and size of the environment. And what you see, for example, if the flag was where that cross was in a small square environment, and then if you ask people where it was, but you've made the environment bigger, where they think the flag had been stretches out in exactly the same way that the place cell firing stretched out. It's as if you remember where the flag was by storing the pattern of firing across all of your place cells at that location, and then you can get back to that location by moving around so that you best match the current pattern of firing of your place cells with that stored pattern. That guides you back to the location that you want to remember.
Nese caso, podemos ver como cambia onde pensan que estaba a bandeira, en función de como cambiamos a forma e o tamaño do medio. Vemos, por exemplo, se a bandeira estaba onda a cruz dun espazo pequeno cadrado e lle preguntamos á xente onde estaba pero aumentamos o espazo, o lugar onde crían que estaba a bandeira amplíase exactamente da mesma maneira que os disparos da célula de lugar. É coma se lembrásedes onde estaba a bandeira gardando o patrón de disparos a través das células de lugar nesa posición, e puidésedes volver á posición movéndovos ata facer coincidir o padrón actual das células de lugar co outro padrón almacenado. Iso guíanos de volta á posición que queremos lembrar.
But we also know where we are through movement. So if we take some outbound path -- perhaps we park and we wander off -- we know because our own movements, which we can integrate over this path roughly what the heading direction is to go back. And place cells also get this kind of path integration input from a kind of cell called a grid cell.
Pero tamén sabemos onde estamos a través do movemento. Se collemos un camiño de saída, quizais aparcamos e damos unha volta, sabemos polos nosos movementos, que podemos integrar nese camiño, cal é a dirección para volver. E as células de lugar tamén integran esa información a través dun tipo de célula chamada célula grella.
Now grid cells are found, again, on the inputs to the hippocampus, and they're a bit like place cells. But now as the rat explores around, each individual cell fires in a whole array of different locations which are laid out across the environment in an amazingly regular triangular grid. And if you record from several grid cells -- shown here in different colors -- each one has a grid-like firing pattern across the environment, and each cell's grid-like firing pattern is shifted slightly relative to the other cells. So the red one fires on this grid and the green one on this one and the blue on on this one.
As células grella tamén se atopan nas entradas ao hipocampo, son un pouco como as células de lugar. Pero neste caso cando a rata explora, cada célula individual dispara a un rango de lugares moi diferentes que están espallados polo medio nunha impresionante rede triangular. E se rastrexades varias células grella, aquí en diferentes cores, cada unha ten un padrón de disparos nese medio como unha rede e o padrón de disparos de cada célula rede cambia lixeiramente en relación coas outras células. Así que a vermella dispara nesta rede e a verde nesta e a azul nesta.
So together, it's as if the rat can put a virtual grid of firing locations across its environment -- a bit like the latitude and longitude lines that you'd find on a map, but using triangles. And as it moves around, the electrical activity can pass from one of these cells to the next cell to keep track of where it is, so that it can use its own movements to know where it is in its environment.
E xuntas, é coma se a rata fixese unha rede virtual de posicións de disparos por todo o medio, un pouco como as liñas de latitude e lonxitude que hai nun mapa pero con triángulos. E ao moverse, a actividade eléctrica pode pasar desde unha destas células á próxima para seguir a pista de onde está, para que poida usar os propios movementos e saber onde está no contorno.
Do people have grid cells? Well because all of the grid-like firing patterns have the same axes of symmetry, the same orientations of grid, shown in orange here, it means that the net activity of all of the grid cells in a particular part of the brain should change according to whether we're running along these six directions or running along one of the six directions in between. So we can put people in an MRI scanner and have them do a little video game like the one I showed you and look for this signal. And indeed, you do see it in the human entorhinal cortex, which is the same part of the brain that you see grid cells in rats.
A xente ten células grella? Ben, que todos os padróns que disparan en rede teñan os mesmos eixes de simetrías, a mesma orientación da rede, en laranxa aquí, quere dicir que a actividade de todas as células grella nun lugar particular do cerebro debería cambiar segundo esteamos correndo nestas seis direccións ou nunha das seis direccións intermedias. Podemos poñer xente nun escáner IRM e darlle un pequeno videoxogo como o que vos amosei e buscar este sinal. E vedes no córtex entorrinal humano, que está na mesma parte do cerebro que as células grella das ratas.
So back to Homer. He's probably remembering where his car was in terms of the distances and directions to extended buildings and boundaries around the location where he parked. And that would be represented by the firing of boundary-detecting cells. He's also remembering the path he took out of the car park, which would be represented in the firing of grid cells. Now both of these kinds of cells can make the place cells fire. And he can return to the location where he parked by moving so as to find where it is that best matches the firing pattern of the place cells in his brain currently with the stored pattern where he parked his car. And that guides him back to that location irrespective of visual cues like whether his car's actually there. Maybe it's been towed. But he knows where it was, so he knows to go and get it.
Así que volvendo a Homer. Estará lembrando onde puxo o coche en termos de distancias e direccións cara a edificios extensos e límites ao redor da posición onde aparcou. E iso estará representado polos disparos de células detectoras de límites. Tamén estará lembrando o camiño que colleu fóra do aparcamento, que estará representado nos disparos de células grella. Ambos os tipos de células poden facer disparar as células. E el pode volver ao lugar onde aparcou movéndose para atopalo ata que encaixe o padrón de disparos das células de lugar co padrón almacenado de onde aparcou o seu coche. E iso guíao de volta á posición independentemente das pistas visuais coma se o seu coche estivese alí. Pode que llo levara o guindastre. Pero el sabe onde estaba, así que sabe onde ir e collelo.
So beyond spatial memory, if we look for this grid-like firing pattern throughout the whole brain, we see it in a whole series of locations which are always active when we do all kinds of autobiographical memory tasks, like remembering the last time you went to a wedding, for example. So it may be that the neural mechanisms for representing the space around us are also used for generating visual imagery so that we can recreate the spatial scene, at least, of the events that have happened to us when we want to imagine them.
Máis alá da memoria espacial, se buscamos este padrón rede a través de todo o cerebro, vémolo nunha serie de posicións que están sempre activas ao facermos tarefas de memoria autobiográfica, como lembrar a última vez que fomos a unha voda. Pode que os mecanismos neuronais para representar o espazo ao noso redor se usen tamén para xerar imaxinaría visual, para que poidamos recrear a escena espacial, polo menos, dos eventos que nos ocorreron cando os imaxinamos.
So if this was happening, your memories could start by place cells activating each other via these dense interconnections and then reactivating boundary cells to create the spatial structure of the scene around your viewpoint. And grid cells could move this viewpoint through that space. Another kind of cell, head direction cells, which I didn't mention yet, they fire like a compass according to which way you're facing. They could define the viewing direction from which you want to generate an image for your visual imagery, so you can imagine what happened when you were at this wedding, for example.
Se isto ocorrese, as vosas memorias comezarían activando entre si as células de lugar a través desas densas conexións e reactivando células límite para crear a estrutura espacial ao redor da vosa perspectiva. E as células grella poderían mover a perspectiva no espazo. Outro tipo de célula, as de dirección da cabeza, que aínda non mencionei, disparan como un compás de acordo co camiño que seguides. Poden definir a dirección da vista desde onde queredes xerar unha imaxe para a vosa imaxinaría visual, así que podedes imaxinar o que ocorreu nesa voda, por exemplo.
So this is just one example of a new era really in cognitive neuroscience where we're beginning to understand psychological processes like how you remember or imagine or even think in terms of the actions of the billions of individual neurons that make up our brains.
Isto é só un exemplo dunha nova era da neurociencia cognitiva, cando comezamos a entender procesos psicolóxicos, como o xeito en que lembramos ou imaxinamos ou mesmo pensamos en termos de accións dos centos de miles de neuronas individuais que forman o cerebro.
Thank you very much.
Moitas grazas.
(Applause)
(Aplausos)