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.
Kada se parkiramo na parkingu, kako se sećamo gde smo ostavili svoj automobil? Ovo je problem sa kojim se Homer suočava. Pokušaćemo da razumemo šta se dešava u njegovom mozgu.
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.
Dakle, počećemo sa hipokampusom, prikazanim žutom bojom, koji je organ memorije. Ako tu imate oštećenje, kao kod Alchajmerove bolesti, ne možete da se setite stvari, uključujući i gde ste parkirali auto. Nazvan je "morski konjić" na latinskom, na kojeg i liči. Kao i ostatak mozga, sačinjen je od neurona.
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.
Dakle, ljudski mozak ima oko stotinu milijardi neurona. Neuroni komuniciraju između sebe slanjem malih električnih potencijala preko međusobnih veza. Hipokampus je građen od dva sloja ćelija, koji su veoma gusto povezani. Naučnici počinju da shvataju kako pamćenje prostora funkcioniše beleženjem aktivnosti pojedinačnih neurona pacova i miševa, dok tragaju za hranom ili istražuju okolinu tražeći hranu.
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?"
Dakle, zamislićemo da snimamo pojedinačni neuron hipokampusa ovog pacova. Kada neuron okine električni potencijal pojaviće se crvena tačka i klik. Dakle, ono što vidimo je da ovaj neuron zna kad god je pacov otišao na određeno mesto u svojoj okolini. On to signalizira ostatku mozga šaljući male impulse elektriciteta. Dakle, možemo da prikažemo obrazac okidanja tog neurona kao funkciju položaja te životnje u prostoru. Ako snimimo aktivnost više neurona, videćemo da različiti neuroni šalju impulse kada životinja ide na različita mesta te sredine, kao u ovoj kvadratnoj kutiji. Dakle, oni zajedno formiraju mapu namenjenu ostatku mozga obaveštavajući ga neprekidno: "Gde sam sad u svom okruženju?"
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.
"Ćelije mesta" su nađene i kod ljudi. Tako je pacijentima sa epilepsijom potrebno nadgledanje električne aktivnosti mozga. Neki od ovih pacijenata igrali su video igricu u kojoj su se vozili po malom gradu. Ćelije mesta njihovog hipokampusa bi se aktivirale i slale električne impulse kad god bi prolazili pored određenog mesta u tom gradu.
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.
Kako ćelije mesta znaju gde je pacov ili čovek unutar svoje okoline? Ove dve ćelije nam pokazuju da su granice sredine posebno važne. Dakle, ova na vrhu voli da šalje signal nekako na pola puta između zidova kutije u kojoj je pacov. A kada proširite kutiju, prostor slanja signala se širi. Ova ispod voli da šalje signal kad god je u blizini južnog zida kutije. Ako postavite još jedan zid unutar kutije, tada ćelija okida impulse na oba mesta kad god postoji zid na jugu, dok životnja istražuje okolo unutar kutije. Dakle, ovim se predviđa da je percepcija graničnih udaljenosti i pravaca oko vas uključujući i zgrade i slično - posebno važna za hipokampus. Zaista, u aferentnim putevima hipokampusa, su ćelije koje se projektuju u hipokampus, koje reaguju upravo pri otkrivanju granica i ivica na određenim odstojanjima i pravcima od pacova ili miša, dok se on kreće i istražuje okolinu.
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.
Dakle, ćelija levo, kao što možete videti, okida kad god se životinja približi zidu ili granici na istoku, bilo da je to ivica ili zid kvadratne kutije ili kružni zid kružne kutije ili čak ivica stola po kom životnja trči. A ova ćelija desno ispaljuje kad god postoji granica na jugu, bez obzira da li je to ivica stola ili zid ili čak prostor između dva razdvojena stola. Mislimo da je to jedan način koji koriste ćelije mesta da bi odredile položaj životinje, dok istražuje okolinu.
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.
Takođe možemo ispitati gde mislimo da su objekti, kao što je ova zastavica, u jednostavnoj sredini ili u stvarnosti, gde bi mogao biti vaš auto. Tako, možemo imati i ljude koji istražuju okolinu i vide mesto koje treba da zapamte. I onda, ako ih vratimo nazad u tu sredinu, u većini slučajeva odrede mesto gde misle da su bili zastavica ili automobil. Ali u nekim ispitivanjima, možemo da promenimo oblik i veličinu okoline kao što smo uradili sa ćelijom mesta.
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.
U tom slučaju, možemo videti kako se njihovo sećanje na položaj zastavice menja zavisno od naše promene izgleda i veličine okoline. I ono što možete videti, na primer, ako je zastavica bila na mestu ovog krsta u malom kvadratu i onda ih pitate gde je bila, a vi ste u međuvremenu učinili prostor većim, mesto gde misle da je bila zastavica se izdužuje na isti način kao što se izdužio prostor aktivnosti ćelija mesta. To je kao da se sećate gde je zastavica bila čuvanjem obrazaca okidanja duž svih svojih ćelija mesta na zadatoj lokaciji, onda možete da se vratite na to mesto krećući se okolo, tako da najbolje usaglasite trenutni obrazac okidanja ćelija mesta sa već sačuvanim obrascem. Ovo vas vodi nazad na mesto koje želite da zapamtite.
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.
Ali, mi znamo gde se nalazimo i pomoću kretanja. Ako posmatramo neki put odlaska - kao kad se parkiramo i posle odlutamo - znamo uz pomoć sopstvenog kretanja, koje možemo da integrišemo preko ovog puta i tako grubo da odredimo glavni pravac povratka. Ćelije mesta takođe dobijaju ovako integrisani unos preko ćelija koje zovemo "ćelijama rešetke".
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.
Ovakve ćelije se nalaze u aferentima hipokampusa i liče na ćelije mesta. Ali sada, kad pacov istražuje svaka ćelija okida impulse sa niza različitih mesta i one su raspoređene po celom prostoru u obliku zapanjujuće pravilne rešetkaste mreže trouglova. Ako beležite aktivnost različitih ćelija rešetke - prikazanih ovde u različitim bojama - svaka prostorno ima obrazac aktivnosti u vidu rešetkaste mreže i svaki pojedinačni obrazac okidanja je malo pomeren u odnosu na druge ćelije. Crvena je aktivna na ovoj mreži zelena na ovoj, a plava na ovoj.
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.
Zajedno, čini se da pacov može da postavi virtuelnu mrežu obrazaca ovih aktivnosti preko celog prostora, slično linijama geografske dužine i širine na mapi, ali koristeći trouglove. Kako se kreće unaokolo, električna aktivnost može da pređe sa jedne od ovih ćelija na sledeću pamteći tako gde se nalazi, tako da koristi sopstveno kretanje da bi znao gde se nalazi u prostoru.
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.
Da li ljudi imaju ove ćelije rešetke? S obzirom da svi rešetkasti obrasci okidanja u vidu mreže imaju istu osu simetrije, odnosno iste orijentacije mreža, prikazane narandžasto, znači da bi ukupna aktivnost svih ćelija rešetke u određenom delu mozga trebalo da se promeni zavisno od toga da li se krećemo duž ovih šest pravaca ili ovih šest pravaca između njih. Možemo da stavimo ljude u skener magnetne rezonance damo im zadatak kao video igricu kao ona koju sam već prikazao i posmatramo ovaj signal. I zaista, to vidite u ljudskom entorinalnom korteksu, što odgovara delu mozga pacova koji sadrži ćelije rešetke.
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.
Dakle, vratimo se Homeru. Verovatno se seća gde mu je automobil, u funkciji udaljenosti i pravaca uključujući zgrade i granice oko mesta gde se parkirao. To bi bilo predstavljeno okidanjem ćelija koje detektuju granice. On se takođe seća puta kojim je izašao iz parkinga, što bi bilo predstavljeno aktivnošću ćelija rešetke. Obe ove vrste ćelija mogu da aktiviraju ćelije mesta. On će se vratiti na mesto gde je parkirao krećući se i pokušavajući da pronađe najbolje preklapanje sadašnjeg obrasca aktivnosti ćelija mesta sa već sačuvanim obrascem gde je parkirao auto. To ga navodi na lokaciju bez obzira na vizualne znakove da li je njegov automobil zapravo tamo. Možda ga je "pauk" odneo. Ali zna gde je bio i zna do njega da dođe.
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.
Osim pamćenja prostora, ako posmatramo ovaj rešetkasti obrazac aktivnosti u celom mozgu, vidimo ga u raznim delovima koji su uvek aktivni kad obavljamo različite autobiografske memorijske aktivnosti, npr. kao što je sećanje kad ste poslednji put bili na venčanju. Moguće je da se neuronski mehanizmi za predstavljanje prostora oko nas takođe koriste za stvaranje vizuelnog sećanja, tako da možemo da rekonstruišemo prostornu scenu onoga što smo doživeli kada želimo da je zamislimo.
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.
Ako se ovo dešava, vaše sećanje bi moglo da započne tako što ćelije mesta aktiviraju jedna drugu preko međusobnih gustih veza, a zatim reaktiviraju ćelije granice da bi stvorile prostorni sklop scene oko vaše tačke gledanja. Ćelije reštke bi mogle da pomeraju ovu tačku gledanja kroz prostor. Druga vrsta ćelija, ćelije pravca glave koje još nisam pomenuo, okidaju kao kompas zavisno od pravca kojem ste okrenuti. One bi mogle da definišu pravac gledanja iz kog ćete stvoriti sliku svog vizuelnog sećanja tako da možete da zamislite šta se dogodilo kad ste bili na tom venčanju.
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.
Ovo je samo jedan primer nove ere kognitivne neuronauke gde počinjemo da razumevamo psihološke procese kao što je kako pamtite ili zamišljate ili čak razmišljate, kao izraz aktivnosti milijardi pojedinačnih neurona koji čine naš mozak.
Thank you very much.
Hvala najlepše.
(Applause)
(Aplauz)