how do we remember where we parked our car?

當我們把車停在一個很大的停車場，

Here's the problem facing Homer.

我們怎麼記住我們停的位置?

And we're going to try to understand

辛普森遇到了一個麻煩

what's happening in his brain.

讓我們試著去了解

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

他的大腦到底發生了甚麼事情

which is the organ of memory.

我們先從他的頭腦內黃色標記的部分

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

也就是記憶的源頭：海馬體

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

如果你腦內的這部分受到損傷，好比阿茲海默症

It's named after Latin for "seahorse,"

你會記不住事情，包括說你把車子停哪

which it resembles.

這個部位是以拉丁文"海馬"所命名的

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

因為它的形狀和海馬相似

So the human brain

就如同腦內其他部位一樣，它是由神經元所構成的

has about a hundred billion neurons in it.

所以在人腦內

And the neurons communicate with each other

有大約好幾百億的神經元

by sending little pulses or spikes of electricity

神經元會利用脈衝或者是電突波發送刺激

via connections to each other.

藉由神經元間的連結

The hippocampus is formed of two sheets of cells,

互相傳遞訊息

which are very densely interconnected.

海馬體是由兩片細胞

And scientists have begun to understand

彼此非常緊密的連結組成

how spatial memory works

近期科學家開始了解

by recording from individual neurons

我們對於空間的記憶是怎們運作的

in rats or mice

藉由記錄老鼠

while they forage or explore an environment

在一個空間中探索

looking for food.

尋找食物時的

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

每一個獨立的神經訊號

in the hippocampus of this rat here.

讓我們來想像我們記錄一個獨立的神經元

And when it fires a little spike of electricity,

在這隻老鼠的海馬體裡面

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

當他發送出一個電的突波時

So what we see

就會有一個紅點來記錄

is that this neuron knows

所以我們可以發現

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

這個神經元知道

And it signals to the rest of the brain

這隻老鼠在這環境中的某一個特定的地方

by sending a little electrical spike.

然後它會藉由電的突波

So we could show the firing rate of that neuron

來傳遞訊號給大腦

as a function of the animal's location.

並且得知神經元的傳送速率

And if we record from lots of different neurons,

是動物在空間的一個位置函數

we'll see that different neurons fire

如果我們紀錄很多不同的神經

when the animal goes in different parts of its environment,

我們可以發現到當動物移動到另外不同位置

like in this square box shown here.

會有不同的神經發射出訊號

So together they form a map

像是圖中是這個方形的空間

for the rest of the brain,

所以由所有神經發射出的訊號

telling the brain continually,

可以讓大腦繪出一張地圖

"Where am I now within my environment?"

持續不斷地告訴大腦

Place cells are also being recorded in humans.

"我現在在這個空間中的哪裡?"

So epilepsy patients sometimes need

同樣的人類的大腦此"位置細胞"也有相同的運作方式

the electrical activity in their brain monitoring.

因此癲癇患者有時候需要

And some of these patients played a video game

藉由控制儀器施予腦部一些電的刺激

where they drive around a small town.

有些病患會玩一個電腦遊戲

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

讓他們在一個小鎮裡面開車閒晃

start sending electrical impulses

當他們經過一個特殊的地點時

whenever they drove through a particular location in that town.

海馬體裡的"位置細胞"就會被活化並且發射出訊號

So how does a place cell know

開始傳送脈衝電訊號

where the rat or person is within its environment?

所底到底一個位置細胞怎麼讓人或老鼠

Well these two cells here

知道自己在環境的某一個位置?

show us that the boundaries of the environment

圖中這兩個細胞

are particularly important.

告訴我們一個極重要的資訊

So the one on the top

也就是環境的邊界

likes to fire sort of midway between the walls

上方那張圖顯示一個神經

of the box that their rat's in.

當老鼠在兩面牆之間時

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

會發出訊號

The one below likes to fire

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

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

下面那張圖顯示一神經

And if you put another wall inside the box,

當南方靠近一面牆的時候會被激發

then the cell fires in both place

如果你在盒子中間放置另一道牆

wherever there's a wall to the south

那細胞在這兩個地方都會被激活

as the animal explores around in its box.

當動物隨意在箱子裡頭探索

So this predicts

不管在哪裡只要南方有一面牆，細胞都會被激發

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

所以可以偵測出

extended buildings and so on --

在你周遭環境的邊界障礙

is particularly important for the hippocampus.

還有一些建築物等等的資訊

And indeed, on the inputs to the hippocampus,

對於海馬體是極為重要的

cells are found which project into the hippocampus,

如同實驗證實，當這些外界的訊號刺激海馬體後

which do respond exactly

海馬體有些細胞會

to detecting boundaries or edges

根據周遭環境，不管是邊界或是端點

at particular distances and directions

並在特定的方向與距離

from the rat or mouse

而有所反應

as it's exploring around.

老鼠就是一個實際實驗的例子

So the cell on the left, you can see,

當它四處遊蕩

it fires whenever the animal gets near

你可以發現在左方的細胞

to a wall or a boundary to the east,

當老鼠碰到東邊的障礙物的時候

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

這個細胞就會被激發

or the circular wall of the circular box

不管是方形的

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

或是圓形的空間

And the cell on the right there

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

fires whenever there's a boundary to the south,

看到這裡右方的細胞

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

當碰到南方邊界或是邊緣的時候

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

會被激發

So that's one way in which we think

不僅如此，細胞也能判斷兩張桌子中間的縫隙

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

因此我們可以推斷

We can also test where we think objects are,

位置細胞可以決定動物所在的方位

like this goal flag, in simple environments --

同樣地藉由位置細胞我們可以判斷出物體的方位

or indeed, where your car would be.

像是一個簡單的環境 - 一個目標旗桿

So we can have people explore an environment

也可能是你車子的位置

and see the location they have to remember.

於是我們可以也讓人去探索一個空間

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

讓他們去記下一些特定的位置

generally they're quite good at putting a marker down

之後，我們再把它放到一個相同的環境

where they thought that flag or their car was.

一般來說他們可以輕易的知道

But on some trials,

先前目標旗桿或是車子擺放的位置

we could change the shape and size of the environment

但是在另外一些試驗當中

like we did with the place cell.

當我們開始改變外在環境的形狀或大小

In that case, we can see

如同先前我們對位置細胞所做的實驗

how where they think the flag had been changes

我們可以發現

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

他們認為旗幟位置的改變

And what you see, for example,

會隨著環境的改變而有所對應

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

從下面這個例子我們可以看到

and then if you ask people where it was,

旗子在方形空間中那個交叉註記的點

but you've made the environment bigger,

在環境變大之前先讓受試者記錄下那個位置

where they think the flag had been

變大後再問一次受試者

stretches out in exactly the same way

問他們認知中旗幟的位置

that the place cell firing stretched out.

結果我們可以發現他們認知中的位置

It's as if you remember where the flag was

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

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

就像是你可以藉由位置細胞記錄下被激發的位置

at that location,

你才可以記住旗幟

and then you can get back to that location

的所在位置

by moving around

讓你之後藉由四處走走

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

找到符合先前位置細胞被激發的區域

with that stored pattern.

也就是比對先前位置細胞激發的模式

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

進而找到目標物的位置

But we also know where we are through movement.

藉由這個模式可以讓你找到你先前記憶的位置

So if we take some outbound path --

除此之外我們也可以知道我們移動期間的位置

perhaps we park and we wander off --

也許我們可能停了車子之後四處閒晃

we know because our own movements,

走了一個不同的路徑

which we can integrate over this path

原因在於

roughly what the heading direction is to go back.

我們會一步步的去記憶所在位置並綜合起來

And place cells also get this kind of path integration input

讓我們可以粗略地知道回去的方向

from a kind of cell called a grid cell.

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

Now grid cells are found, again,

這種類型的細胞叫做「網格細胞」

on the inputs to the hippocampus,

此細胞也是在

and they're a bit like place cells.

腦內海馬裡裡面找到

But now as the rat explores around,

它有點類似位置細胞

each individual cell fires

當老鼠四處移動的時候

in a whole array of different locations

每個網格細胞會激發並記錄

which are laid out across the environment

一連串的不同方向的位置

in an amazingly regular triangular grid.

並在一個整個空間當中

And if you record from several grid cells --

呈現出令人驚訝的一個三角形網格

shown here in different colors --

如果你紀錄數組網格細胞

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

並以不同的顏色標記

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

你會發現在空間中被激發的模式就像是一格一格的網格

relative to the other cells.

每一個細胞的網格激發模式會和與相鄰的網格

So the red one fires on this grid

做些微的位移

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

像是圖中紅色的會在這個網格被激發

So together, it's as if the rat

綠色的在這個，藍色的在另外一個

can put a virtual grid of firing locations

綜合起來，老鼠就可以

across its environment --

藉由這些細胞被激發的位置

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

建構出一個虛擬空間的網路

but using triangles.

這個運作方式就像是地圖上網格，也就是經度和緯度

And as it moves around,

只是在這裡網格細胞是用三角形的網格

the electrical activity can pass

當老鼠四處移動的時候

from one of these cells to the next cell

它腦內的電訊號

to keep track of where it is,

會由這個細胞傳遞到下一個細胞

so that it can use its own movements

使老鼠得以追蹤自己的所在地

to know where it is in its environment.

因此老鼠才可以藉由自己的移動

Do people have grid cells?

知道自己在空間中的位置

Well because all of the grid-like firing patterns

所以到底人類腦內有沒有類似的網格細胞呢?

have the same axes of symmetry,

先從網格細胞激發網格的對稱性說起

the same orientations of grid, shown in orange here,

他們有著相同的對稱軸

it means that the net activity

橘色標出的部分，也就是網格也有固定的方向性

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

意思是說整個網格的運作

should change

會根據位置在

according to whether we're running along these six directions

三個軸六個方向

or running along one of the six directions in between.

之間的移動

So we can put people in an MRI scanner

而有所改變

and have them do a little video game

要釐清這個問題，我們可以試著讓受試者

like the one I showed you

在一個核磁共振的儀器內玩一個

and look for this signal.

我們先前提過的一個虛擬遊戲

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

同時我們去尋找並記錄網格訊號

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

結果如我們預測，在人腦內類似於老鼠網格細胞所在

So back to Homer.

一個叫做「內鼻皮質層」的地方

He's probably remembering where his car was

讓我們再一次回到辛普森的故事

in terms of the distances and directions

它可能藉由記憶他車子的位置和方向

to extended buildings and boundaries

並記錄與邊界或者是建築物的相對位置

around the location where he parked.

來找到他

And that would be represented

停車的地方

by the firing of boundary-detecting cells.

這個過程可以視為

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

邊界偵測細胞的展現

which would be represented in the firing of grid cells.

同時藉由網格細胞激發模式的記憶

Now both of these kinds of cells

知道他要怎麼走出這座停車場

can make the place cells fire.

兩種不同類型的細胞

And he can return to the location where he parked

綜合起來可以使位置細胞被激發

by moving so as to find where it is

讓他可以藉由移動

that best matches the firing pattern

找到他當初車子停放的位置

of the place cells in his brain currently

也就找到目前位置

with the stored pattern where he parked his car.

與記憶中車子停放的地方，位置細胞的激發模式去做比對

And that guides him back to that location

所相雷同的模式

irrespective of visual cues

藉此方法可以導引辛普森到他停車的位置

like whether his car's actually there.

和任何的視覺提示沒有太大的關係

Maybe it's been towed.

一種狀況是儘管車子被拖吊

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

讓車子不在目標位置上

So beyond spatial memory,

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

if we look for this grid-like firing pattern

更深入地去探究空間記憶

throughout the whole brain,

如果我們觀察整個腦內的

we see it in a whole series of locations

網格狀激發模式

which are always active

我們可以發現腦內一些相關的位置

when we do all kinds of autobiographical memory tasks,

會隨時都處在被活化的狀態

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

當我們在記憶像是你上次參加婚禮的地方

So it may be that the neural mechanisms

的一些特徵記憶工作時

for representing the space around us

神經運作機制會扮演很重要的角色

are also used for generating visual imagery

例如周遭所呈現的環境

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

或是呈現一些視覺上的影像

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

好讓我們能夠輕易地去

So if this was happening,

重溫發生在我們生命中的景事物

your memories could start by place cells activating each other

如果這些研究進一步被證實

via these dense interconnections

你的記憶其實是從緊密互相連結的

and then reactivating boundary cells

位置細胞作相互的活化激發

to create the spatial structure

然後重新活化邊界細胞

of the scene around your viewpoint.

以產在你眼睛所及的

And grid cells could move this viewpoint through that space.

整個空間架構所來

Another kind of cell, head direction cells,

而後網格細胞可以藉由紀錄空間去移動這個視野

which I didn't mention yet,

另外一種我還沒提過的細胞

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

頭向細胞(Head Direction cells)

They could define the viewing direction

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

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

藉由你視覺上的景象

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

可以自由地定義你的方向

So this is just one 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

of a new era really

綜觀以上介紹

in cognitive neuroscience

都是認知神經科學中

where we're beginning to understand

嶄新的一個領域

psychological processes

我們漸漸地開始了解

like how you remember or imagine or even think

整個神經認知的過程

in terms of the actions

像是你怎麼去記憶，怎麼去想像，甚至是怎麼去思考

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

都是藉由數十億個獨立神經元所構成的腦

Thank you very much.

相互的運作

(Applause)

感謝聆聽