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 parkiramo na velikom parkiralištu, kako se sjetimo gdje smo ostavili auto? Ovaj problem muči Homera. Pokušat ćemo razumjeti što se događa 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.
Počnimo s hipokampusom, koji je obojan žuto, i organ je memorije. Ako imate neko oštećenje na tom području, kao kod Alzheimerove bolesti, ne možete zapamtiti stvari poput toga gdje ste parkirali. Hipokampus je dobio ime po latinskom nazivu za morskog konjica, na kojeg izgledom podsjeća. Kao i ostatak mozga, načinjen 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.
Ljudski mozak sadrži otprilike stotinu milijardi neurona. Ti neuroni međusobno komuniciraju, šalju si male električne signale preko različitih veza kojima su povezani. Hipokampus se sastoji od dvije ploče stanica koje su vrlo gusto povezane. Znanstvenici su počeli shvaćati kako funkcionira prostorna memorija snimajući aktivnost pojedinih neurona kod štakora ili miševa koji su istraživali okolinu u potrazi za hranom.
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?"
Sada ćemo zamisliti da snimamo aktivnost jednog neurona u hipokampusu ovog štakora ovdje. Kada neuron bude odaslao jedan impuls elektriciteta, ovdje ćemo vidjeti crvenu točku i začuti klik. Vidimo da taj neuron zna je li štakor otišao na točno određeno mjesto u okolini. I šalje signal ostatku mozga tim jednim električnim impulsom. Dakle, možemo prikazati jačinu tog impulsa kao funkciju lokacije životinje. I ako snimimo aktivnost više neurona, vidjet ćemo da različiti neuroni šalju impulse kako životinja ide u različite dijelove okoline, kao u ovom kvadratiću ovdje. Zajedno, oni čine mapu za ostatak mozga, neprekidno govoreći mozgu, “Gdje se sada nalazim unutar moje okoline?”
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.
Aktivnost stanica zaduženih za lociranje također je snimana i kod ljudi. Osobe koje boluju od epilepsije katkada trebaju električnu aktivnost pri nadziranju moždanih funkcija. Neki od njih su igrali video igricu u kojoj voze auto po malenom gradiću. Stanice njihovog hipokampusa bi odaslale impuls, aktivirale se i slale signal kad god bi oni provezli auto kroz točno određeno mjesto u tom gradiću.
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 stanica za lociranje zna gdje se štakor ili osoba nalaze? Ove dvije stanice ovdje pokazuju nam da su granice okoline osobito važne. Ova gornja voli slati signal s polovice puta između zidova kutije u kojoj se štakor nalazi. A kada proširite kutiju, i preferirana lokacija za odašiljanje signala se proširi. Donja stanica voli slati signal uvijek kada postoji zid u blizini juga. I ako postavite još jedan zid u kutiju, stanica će slati signal s oba mjesta, gdje god je zid u blizini juga, kako životinja bude istraživala oko kutije. Ovo ukazuje kako je osjećaj za udaljenost i smjer u kojem se nalaze granice oko vas (u proširenom smislu zgrade itd.) povezan s hipokampusom. I zaista, jedan od aferentnih putova za hipokampus, stanice koje šalju projekcije u hipokampus, reagiraju upravo detektirajući granice i rubove na posebnim udaljenostima i pravcima od štakora ili miša dok istražuje uokolo.
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.
Stanica s lijeve strane, kao što vidite, odašilje signal kada se životinja nađe kod zida ili granice blizu istoka, bio to ugao ili zid četvrtaste kutije, zaobljen zid okrugle kutije ili pak rub stola po kojem životinja hoda. Stanica desno odašilje signal kada postoji granica prema jugu, bio to rub stola ili mali prostor između dva spojena stola. Mislimo kako je to jedan od načina na koji stanice za lociranje određuju gdje se životinja nalazi.
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.
Možemo testirati i osjećaj smještanja objekata u prostor, poput ove zastavice, u jednostavnim uvjetima, tj. gdje bi se mogao nalaziti vaš auto. Na početku imamo ispitanike koji promatraju okolinu i lokaciju koju moraju upamtiti. Kada ih poslije vratimo u istu okolinu, generalno su prilično dobri u smještanju oznake na mjesto na kojem je prije bila zastavica ili auto. Možemo mijenjati oblik i veličinu okoline kao što smo radili sa stanicama za lociranje.
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, vidjet ćemo da se njihovo mišljenje o tome gdje je zastavica bila mijenja ovisno o promjeni oblika i veličine okoline. Na primjer, ako je zastavica bila gdje se nalazi križić u maloj četvrtastoj okolini i pitamo ljude gdje je bila, ali povećamo okolinu – njihova predodžba o mjestu na kojem se zastavica nalazila se proširuje isto kao što se proširilo i područje na kojem stanice za lociranje odašilju impuls. Čini se da pamtimo gdje se zastavica nalazila pohranjujući uzorke odašiljanja impulsa svih stanica za lociranje na toj lokaciji. Možemo se vratiti na tu lokaciju kružeći uokolo tako što ćemo povezati trenutne uzorke odašiljanja impulsa stanica za lociranje sa onima koje smo pohranili. To nas vodi natrag k lokaciji koju trebamo upamtiti.
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 također znamo gdje se nalazimo kroz pokret. Ako krenemo nekim izlaznim putem, na primjer parkiramo i odlutamo, sjećamo se svojih pokreta, možemo ih ponovno ugrubo integrirati te pronaći put natrag. Stanice za lociranje također dobivaju projekciju tog tipa od tzv. rešetkastih stanica.
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.
Rešetkaste stanice pojavljuju se kao projekcija u hipokampusu i nalik su stanicama za lociranje. Kako štakor istražuje okolinu, svaka individualna stanica ispaljuje na nizu različitih lokacija koje su posložene u nevjerojatno pravilan trokutast oblik. I ako snimimo aktivnost više različitih rešetkastih stanica – što vidimo ovdje prikazano različitim bojama – svaka ima uzorak nalik rešetki uzduž okoline, i svaki taj uzorak je malo pomaknut u odnosu na uzorke ostalih stanica. Crvena formira ovu rešetku, zelena ovu, a plava ovu.
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.
Dakle, to je kao da štakor na temelju svoje okoline sastavlja virtualnu rešetku lokacija na kojima se odašilje impuls – nešto poput okomitih i vodoravnih linija koje možete naći na karti, samo koristi trokute. Kako se kreće uokolo, električna aktivnost prelazi s jedne na drugu stanicu i bilježi gdje se štakor nalazi, tako da on može znati gdje se nalazi koristeći vlastite kretnje.
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.
Imaju li ljudi rešetkaste stanice? Budući da svi rešetkasti uzorci impulsa imaju iste osi simetrije, istu orijentaciju rešetki, što je prikazano ovdje narančasto, to bi značilo da mrežastu aktivnost svih rešetkastih stanica određenog dijela mozga možemo mijenjati ovisno o tome krećemo li se uzduž jednog od ovih šest pravaca ili jednog od šest pravaca između. Ljude možemo podvrgnuti MRI skeniranju dok igraju video igru poput one koju sam vam pokazao. i tražiti taj signal. I zaista, taj signal možete vidjeti u ljudskom entorinalnom korteksu, koji se nalazi na istom dijelu mozga na kojem kod štakora nalazimo rešetkaste stanice.
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.
Vratimo se Homeru. Vjerojatno se sjeća gdje mu se nalazi auto u smislu udaljenosti te pravca zgrada i granica koje okružuju mjesto na kojemu je parkirao. I to bismo vidjeli kao odašiljanje signala stanica koje detektiraju granice. Također, sjeća se i puta kojim je krenuo s parkirališta, a to bismo vidjeli kao odašiljanje signala rešetkastih stanica. Obje vrste stanica mogu dovesti do odašiljanja signala iz stanica za lociranje. Homer se može vratiti do mjesta gdje se parkirao tražeći mjesto na kojem se trenutno odašiljanje stanica za lociranje najbolje poklapa s upamćenim uzorkom odašiljanja signala. To ga vodi natrag na lokaciju bez obzira na vizualne znakove poput toga je li njegov auto zbilja tamo. Možda ga je pauk odnio. Ali on zna gdje je bio, tako da zna i otići po njega.
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.
S druge strane, ako pogledamo ove rešetkaste uzorke odašiljanja impulsa kroz cijeli mozak, vidimo serije lokacija koje su aktivne uvijek kada obavljamo razne zadatke vezane uz autobiografsko sjećanje, na primjer prisjećanje kada smo zadnji put bili na vjenčanju. Moguće je da se neuralni mehanizmi za prikazivanje prostora oko nas koriste ujedno i za generiranje vizualnih slika kako bismo mogli stvoriti prostorni prizor događaja koji su nam se dogodili kada ih se želimo prisjetiti.
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 to događa na taj način, prisjećanje počinje tako što se stanice za lociranje međusobno aktiviraju putem gustih komunikacija, reaktiviraju stanice za detektiranje granica kako bi stvorile prostornu strukturu prizora s vaše točke gledišta. Rešetkaste stanice pomiču tu točku gledišta kroz prostor. Još jedna vrsta stanica koju dosad nisam spominjao, stanice koje određuju smjer gibanja glave odašilju impulse poput kompasa ovisno o tome na koju stranu ste okrenuti. One definiraju pravac gledanja s kojeg želite generirati imaginarnu sliku, tako da na primjer, možete zamisliti što se događalo kada ste bili na tom vjenčanju.
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 još jedan dokaz o novom dobu koje je nastupilo u neuroznanosti, gdje počinjemo shvaćati psihičke procese poput toga kako se prisjećamo, kako zamišljamo ili mislimo u okvirima aktivnosti milijardi individualnih neurona koji sačinjavaju naš mozak.
Thank you very much.
Hvala puno.
(Applause)
(Pljesak)