Neil Burgess: How your brain tells you where you are

譯者: Sean Chuang 審譯者: Meg Lee

When we park in a big parking lot,

當我們把車停在一個很大的停車場，

how do we remember where we parked our car?

我們怎麼記住我們停的位置?

Here's the problem facing Homer.

辛普森遇到了一個麻煩

And we're going to try to understand

讓我們試著去了解

what's happening in his brain.

他的大腦到底發生了甚麼事情

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

我們先從他的頭腦內黃色標記的部分

which is the organ of memory.

也就是記憶的源頭：海馬體

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

如果你腦內的這部分受到損傷，好比阿茲海默症

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

你會記不住事情，包括說你把車子停哪

It's named after Latin for "seahorse,"

這個部位是以拉丁文"海馬"所命名的

which it resembles.

因為它的形狀和海馬相似

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

就如同腦內其他部位一樣，它是由神經元所構成的

So the human brain

所以在人腦內

has about a hundred billion neurons in it.

有大約好幾百億的神經元

And the neurons communicate with each other

神經元會利用脈衝或者是電突波發送刺激

by sending little pulses or spikes of electricity

藉由神經元間的連結

via connections to each other.

互相傳遞訊息

The hippocampus is formed of two sheets of cells,

海馬體是由兩片細胞

which are very densely interconnected.

彼此非常緊密的連結組成

And scientists have begun to understand

近期科學家開始了解

how spatial memory works

我們對於空間的記憶是怎們運作的

by recording from individual neurons

藉由記錄老鼠

in rats or mice

在一個空間中探索

while they forage or explore an environment

尋找食物時的

looking for food.

每一個獨立的神經訊號

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

讓我們來想像我們記錄一個獨立的神經元

in the hippocampus of this rat here.

在這隻老鼠的海馬體裡面

And when it fires a little spike of electricity,

當他發送出一個電的突波時

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

就會有一個紅點來記錄

So what we see

所以我們可以發現

is that this neuron knows

這個神經元知道

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

這隻老鼠在這環境中的某一個特定的地方

And it signals to the rest of the brain

然後它會藉由電的突波

by sending a little electrical spike.

來傳遞訊號給大腦

So we could show the firing rate of that neuron

並且得知神經元的傳送速率

as a function of the animal's location.

是動物在空間的一個位置函數

And if we record from lots of different neurons,

如果我們紀錄很多不同的神經

we'll see that different neurons fire

我們可以發現到當動物移動到另外不同位置

when the animal goes in different parts of its environment,

會有不同的神經發射出訊號

like in this square box shown here.

像是圖中是這個方形的空間

So together they form a map

所以由所有神經發射出的訊號

for the rest of the brain,

可以讓大腦繪出一張地圖

telling the brain continually,

持續不斷地告訴大腦

"Where am I now within my environment?"

"我現在在這個空間中的哪裡?"

Place cells are also being recorded in humans.

同樣的人類的大腦此"位置細胞"也有相同的運作方式

So epilepsy patients sometimes need

因此癲癇患者有時候需要

the electrical activity in their brain monitoring.

藉由控制儀器施予腦部一些電的刺激

And some of these patients played a video game

有些病患會玩一個電腦遊戲

where they drive around a small town.

讓他們在一個小鎮裡面開車閒晃

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

當他們經過一個特殊的地點時

start sending electrical impulses

海馬體裡的"位置細胞"就會被活化並且發射出訊號

whenever they drove through a particular location in that town.

開始傳送脈衝電訊號

So how does a place cell know

所底到底一個位置細胞怎麼讓人或老鼠

where the rat or person is within its environment?

知道自己在環境的某一個位置?

Well these two cells here

圖中這兩個細胞

show us that the boundaries of the environment

告訴我們一個極重要的資訊

are particularly important.

也就是環境的邊界

So the one on the top

上方那張圖顯示一個神經

likes to fire sort of midway between the walls

當老鼠在兩面牆之間時

of the box that their rat's in.

會發出訊號

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

當盒子的空間擴大的時候，神經被激發的位置也會隨之擴大

The one below likes to fire

下面那張圖顯示一神經

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

當南方靠近一面牆的時候會被激發

And if you put another wall inside the box,

如果你在盒子中間放置另一道牆

then the cell fires in both place

那細胞在這兩個地方都會被激活

wherever there's a wall to the south

當動物隨意在箱子裡頭探索

as the animal explores around in its box.

不管在哪裡只要南方有一面牆，細胞都會被激發

So this predicts

所以可以偵測出

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

在你周遭環境的邊界障礙

extended buildings and so on --

還有一些建築物等等的資訊

is particularly important for the hippocampus.

對於海馬體是極為重要的

And indeed, on the inputs to the hippocampus,

如同實驗證實，當這些外界的訊號刺激海馬體後

cells are found which project into the hippocampus,

海馬體有些細胞會

which do respond exactly

根據周遭環境，不管是邊界或是端點

to detecting boundaries or edges

並在特定的方向與距離

at particular distances and directions

而有所反應

from the rat or mouse

老鼠就是一個實際實驗的例子

as it's exploring around.

當它四處遊蕩

So the cell on the left, you can see,

你可以發現在左方的細胞

it fires whenever the animal gets near

當老鼠碰到東邊的障礙物的時候

to a wall or a boundary to the east,

這個細胞就會被激發

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

不管是方形的

or the circular wall of the circular box

或是圓形的空間

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

當動物在桌子上遊盪當碰到桌緣的時候腦部細胞的活動也大致相同

And the cell on the right there

看到這裡右方的細胞

fires whenever there's a boundary to the south,

當碰到南方邊界或是邊緣的時候

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

會被激發

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

不僅如此，細胞也能判斷兩張桌子中間的縫隙

So that's one way in which we think

因此我們可以推斷

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

位置細胞可以決定動物所在的方位

We can also test where we think objects are,

同樣地藉由位置細胞我們可以判斷出物體的方位

like this goal flag, in simple environments --

像是一個簡單的環境 - 一個目標旗桿

or indeed, where your car would be.

也可能是你車子的位置

So we can have people explore an environment

於是我們可以也讓人去探索一個空間

and see the location they have to remember.

讓他們去記下一些特定的位置

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

之後，我們再把它放到一個相同的環境

generally they're quite good at putting a marker down

一般來說他們可以輕易的知道

where they thought that flag or their car was.

先前目標旗桿或是車子擺放的位置

But on some trials,

但是在另外一些試驗當中

we could change the shape and size of the environment

當我們開始改變外在環境的形狀或大小

like we did with the place cell.

如同先前我們對位置細胞所做的實驗

In that case, we can see

我們可以發現

how where they think the flag had been changes

他們認為旗幟位置的改變

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

會隨著環境的改變而有所對應

And what you see, for example,

從下面這個例子我們可以看到

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

旗子在方形空間中那個交叉註記的點

and then if you ask people where it was,

在環境變大之前先讓受試者記錄下那個位置

but you've made the environment bigger,

變大後再問一次受試者

where they think the flag had been

問他們認知中旗幟的位置

stretches out in exactly the same way

結果我們可以發現他們認知中的位置

that the place cell firing stretched out.

會同於位置細胞被激發的地方並往空間擴大的方向作延展

It's as if you remember where the flag was

就像是你可以藉由位置細胞記錄下被激發的位置

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

你才可以記住旗幟

at that location,

的所在位置

and then you can get back to that location

讓你之後藉由四處走走

by moving around

找到符合先前位置細胞被激發的區域

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

也就是比對先前位置細胞激發的模式

with that stored pattern.

進而找到目標物的位置

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

藉由這個模式可以讓你找到你先前記憶的位置

But we also know where we are through movement.

除此之外我們也可以知道我們移動期間的位置

So if we take some outbound path --

也許我們可能停了車子之後四處閒晃

perhaps we park and we wander off --

走了一個不同的路徑

we know because our own movements,

原因在於

which we can integrate over this path

我們會一步步的去記憶所在位置並綜合起來

roughly what the heading direction is to go back.

讓我們可以粗略地知道回去的方向

And place cells also get this kind of path integration input

位置細胞裡面也會類似去接受並記錄每一個位置並綜合起來

from a kind of cell called a grid cell.

這種類型的細胞叫做「網格細胞」

Now grid cells are found, again,

此細胞也是在

on the inputs to the hippocampus,

腦內海馬裡裡面找到

and they're a bit like place cells.

它有點類似位置細胞

But now as the rat explores around,

當老鼠四處移動的時候

each individual cell fires

每個網格細胞會激發並記錄

in a whole array of different locations

一連串的不同方向的位置

which are laid out across the environment

並在一個整個空間當中

in an amazingly regular triangular grid.

呈現出令人驚訝的一個三角形網格

And if you record from several grid cells --

如果你紀錄數組網格細胞

shown here in different colors --

並以不同的顏色標記

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

你會發現在空間中被激發的模式就像是一格一格的網格

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

每一個細胞的網格激發模式會和與相鄰的網格

relative to the other cells.

做些微的位移

So the red one fires on this grid

像是圖中紅色的會在這個網格被激發

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

綠色的在這個，藍色的在另外一個

So together, it's as if the rat

綜合起來，老鼠就可以

can put a virtual grid of firing locations

藉由這些細胞被激發的位置

across its environment --

建構出一個虛擬空間的網路

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

這個運作方式就像是地圖上網格，也就是經度和緯度

but using triangles.

只是在這裡網格細胞是用三角形的網格

And as it moves around,

當老鼠四處移動的時候

the electrical activity can pass

它腦內的電訊號

from one of these cells to the next cell

會由這個細胞傳遞到下一個細胞

to keep track of where it is,

使老鼠得以追蹤自己的所在地

so that it can use its own movements

因此老鼠才可以藉由自己的移動

to know where it is in its environment.

知道自己在空間中的位置

Do people have grid cells?

所以到底人類腦內有沒有類似的網格細胞呢?

Well because all of the grid-like firing patterns

先從網格細胞激發網格的對稱性說起

have the same axes of symmetry,

他們有著相同的對稱軸

the same orientations of grid, shown in orange here,

橘色標出的部分，也就是網格也有固定的方向性

it means that the net activity

意思是說整個網格的運作

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

會根據位置在

should change

三個軸六個方向

according to whether we're running along these six directions

之間的移動

or running along one of the six directions in between.

而有所改變

So we can put people in an MRI scanner

要釐清這個問題，我們可以試著讓受試者

and have them do a little video game

在一個核磁共振的儀器內玩一個

like the one I showed you

我們先前提過的一個虛擬遊戲

and look for this signal.

同時我們去尋找並記錄網格訊號

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

結果如我們預測，在人腦內類似於老鼠網格細胞所在

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

一個叫做「內鼻皮質層」的地方

So back to Homer.

讓我們再一次回到辛普森的故事

He's probably remembering where his car was

它可能藉由記憶他車子的位置和方向

in terms of the distances and directions

並記錄與邊界或者是建築物的相對位置

to extended buildings and boundaries

來找到他

around the location where he parked.

停車的地方

And that would be represented

這個過程可以視為

by the firing of boundary-detecting cells.

邊界偵測細胞的展現

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

同時藉由網格細胞激發模式的記憶

which would be represented in the firing of grid cells.

知道他要怎麼走出這座停車場

Now both of these kinds of cells

兩種不同類型的細胞

can make the place cells fire.

綜合起來可以使位置細胞被激發

And he can return to the location where he parked

讓他可以藉由移動

by moving so as to find where it is

找到他當初車子停放的位置

that best matches the firing pattern

也就找到目前位置

of the place cells in his brain currently

與記憶中車子停放的地方，位置細胞的激發模式去做比對

with the stored pattern where he parked his car.

所相雷同的模式

And that guides him back to that location

藉此方法可以導引辛普森到他停車的位置

irrespective of visual cues

和任何的視覺提示沒有太大的關係

like whether his car's actually there.

一種狀況是儘管車子被拖吊

Maybe it's been towed.

讓車子不在目標位置上

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

但他可以確定車子曾經在那個地方，並知道要到那個地方去取他的車

So beyond spatial memory,

更深入地去探究空間記憶

if we look for this grid-like firing pattern

如果我們觀察整個腦內的

throughout the whole brain,

網格狀激發模式

we see it in a whole series of locations

我們可以發現腦內一些相關的位置

which are always active

會隨時都處在被活化的狀態

when we do all kinds of autobiographical memory tasks,

當我們在記憶像是你上次參加婚禮的地方

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

的一些特徵記憶工作時

So it may be that the neural mechanisms

神經運作機制會扮演很重要的角色

for representing the space around us

例如周遭所呈現的環境

are also used for generating visual imagery

或是呈現一些視覺上的影像

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

好讓我們能夠輕易地去

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

重溫發生在我們生命中的景事物

So if this was happening,

如果這些研究進一步被證實

your memories could start by place cells activating each other

你的記憶其實是從緊密互相連結的

via these dense interconnections

位置細胞作相互的活化激發

and then reactivating boundary cells

然後重新活化邊界細胞

to create the spatial structure

以產在你眼睛所及的

of the scene around your viewpoint.

整個空間架構所來

And grid cells could move this viewpoint through that space.

而後網格細胞可以藉由紀錄空間去移動這個視野

Another kind of cell, head direction cells,

另外一種我還沒提過的細胞

which I didn't mention yet,

頭向細胞(Head Direction cells)

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

他們就像是指南針一樣可以根據面向不同的方向而有不同的激發模式

They could define the viewing direction

藉由你視覺上的景象

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

可以自由地定義你的方向

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

舉例來說，你可以想像當你在這場婚禮的時後發生了什麼事

So this is just one example

綜觀以上介紹

of a new era really

都是認知神經科學中

in cognitive neuroscience

嶄新的一個領域

where we're beginning to understand

我們漸漸地開始了解

psychological processes

整個神經認知的過程

like how you remember or imagine or even think

像是你怎麼去記憶，怎麼去想像，甚至是怎麼去思考

in terms of the actions

都是藉由數十億個獨立神經元所構成的腦

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

相互的運作

Thank you very much.

感謝聆聽

(Applause)

(掌聲)