Language and the brain: Aphasia and split-brain patients | MCAT | Khan Academy


You may perceive language
as one big function the brain performs. Interestingly,
though, it’s divided into a lot of sub-functions. In this video, we’ll discuss
how your brain speaks and understands
language and what happens when those
functions are disrupted. First, let’s go over
some basic neuroanatomy. For about 90% of
right-handed people, language functions
are centralized in the left hemisphere
of the brain. Lefties and ambidextrous
folks are somewhat more likely to have
language centralized in the right hemisphere,
but still about 70% of them will have language centralized
in the left hemisphere. Within whichever
hemisphere is dominant, the two main areas
associated with language are Broca’s area,
which helps us speak, and Wernicke’s area, which
helps us understand language. Broca’s area is in the
frontal lobe, usually the left frontal lobe, and
it’s responsible for language expression. When Broca’s area
is damaged, people tend to have trouble
producing speech. Their words become
halting or slurred. This is called non-fluent
aphasia, or Broca’s aphasia. I remember this by thinking
that Broca’s aphasia means “broken speech,” and aphasia
is just any type of disorder that involves language. When Wernicke’s area, back in
the temporal lobe, is damaged, you get Wernicke’s
aphasia, which is quite a different
pattern of behavior than you get with
Broca’s apahasia. People have no trouble
producing words– in fact, words kind of
just tumble out of them– but the words that do come
out don’t make any sense. It’s like listening to a
bunch of nonsense sentences. People with Wernicke’s aphasia,
which is also sometimes called “fluent aphasia,” can also
have trouble understanding what other people say. And when both Broca’s aphasia
and Wernicke’s aphasia are present, then
you have something called “global aphasia,” because
it globally affects language instead of only affecting
a subsection of it. Broca’s area and Wernicke’s
area are connected in the brain by a bundle of nerve fibers
called the arcuate fasciculus. One cool thing is
that this loop is also found in deaf people
who know sign language. So it’s not specific
to a spoken language, but the brain adapts to
use whatever modality is necessary for communication. When this connection
is damaged, people experience something called
“conduction aphasia.” Their ability to conduct
information between listening and speaking is
disrupted, which makes them unable to repeat
things, even though they understand what’s being said. Pretty crazy. And once you think
about how many language-specific
functions you do every day, you might wonder how many
different types of aphasia there are. And the answer is “a lot.” We have agraphia, which
is the inability to write, anomia, which is the
inability to name things, and other specific difficulties
in reading, spelling, grammar, pronunciation–
all sorts of things you may not even realize
that you do effortlessly with a healthy brain. But Broca’s apahasia
and Wernicke’s aphasia are the most common. Language is just one example of
how our brain works in general. Big tasks are subdivided into
small tasks, which are then spread around in different
parts of the brain. And this can actually
be a good thing, because it means if you have
very localized or very specific brain damage, then you
probably won’t completely lose your ability to perform
some highly important function like communication. In fact, when functions
are divided like that, it’s easier for
your brain to adapt. For example, when
people have strokes that affect the left
hemisphere of their brain, they may have trouble
speaking or something right after the stroke, but over
time and with proper therapy, some of those people
are able to retrain other speech-related
parts of their brain by creating new connections
between neurons. Building these
connections, in combination with some recovery of the
originally damaged part of the brain, can help
these people speak again with at least some
degree of fluency. And the brain’s ability to adapt
and move functions to new parts is called neural plasticity,
or synaptic plasticity. The neurons are plastic,
or flexible enough, to learn new routes and
connections, thus allowing undamaged parts of
the brain to take over functions that the damaged
parts previously performed. Even with perfectly
functioning hemispheres, you might still have
trouble naming objects. This can happen if communication
between the hemispheres is disrupted by severing
the corpus callosum, which is a band of nerve fibers
that connects your brain’s two hemispheres. This creates what’s called
a split-brain patient, because your brain is
now split into two parts. People used to have
to do this sometimes as a treatment for
seizures, but in addition to helping with that
problem, this surgery creates some pretty
interesting side effects in terms of language. So assuming that
language is centralized in the left
hemisphere, this means that the right
side of your brain can’t connect to
the language side. So anything that you perceive
in the right side of your brain can’t be named or dealt
with in terms of language. Now, you may have heard
before that your brain has what’s called a contralateral
organization, meaning that information
that you perceive in your left visual field gets
processed by the right side of your brain and vice-versa. So let’s think about
what that means for a split-brain patient. If you see an
object on your left, and it gets sent to
your right hemisphere, you won’t be able to name it. You’d still be able to pick
it up with your left hand, because again, your right
hemisphere is controlling your left-side motor neurons,
but you’d have to kind of turn your head so that
the object would be in your right visual
field before the language part of your brain would
have any access to it. Now, when I say the
right visual field, that doesn’t mean
just your right eye. It means the right side
of your body, which you can view with
half of each eye. So there you go. Lots of pretty cool implications
for how our brain is organized and subdivided in
terms of language.

51 Replies to “Language and the brain: Aphasia and split-brain patients | MCAT | Khan Academy

  1. I don`t get it, if you`re a split brain patient, how come your hemispheres can control the contralateral parts of your body?
    Motor commands get sent from the (for example) right hemisphere to the left side of your brain through the corpus callosum, right? 

  2. This is a great explanation, especially for those who suffer from aphasia.  A family member had a stroke several years ago and suffers from aphasia, she has been fighting ever since to understand what happened to her and to be able to explain to others.  Having aphasia makes this very difficult.  Videos like this are very helpful, so thank you!

  3. Language and the brain: Aphasia and split-brain patients
    語言和大腦:失語症和裂腦患者

    You may perceive language as one big function the brain performs.
    你可能認為語言是大腦執行的一大功能。
    Interestingly, though, it’s divided into a lot of sub-functions.
    然而,有趣的是,它被劃分成很多子功能。
    In this video, we’ll discuss how your brain speaks and understands language and what happens when those functions are disrupted.
    在此影片中,我們將會討論到如何運用大腦說話和理解語言,以及,當這些功能被破壞會發生什麼事。
    First, let’s go over some basic neuroanatomy.
    首先,讓我們複習一些基礎的神經解剖學。
    For about 90% of right-handed people, language functions are centralized in the left hemisphere of the brain.
    約90%右撇子的人,語言功能都集中在大腦的左半球。
    Lefties and ambidextrous folks are somewhat more likely to have language centralized in the right hemisphere, but still about 70% of them will have language centralized in the left hemisphere.
    左撇子和靈巧的人更有可能有語言功能集中在右半球,但他們的語言功能仍約 有70%集中在左半球。
    Within whichever hemisphere is dominant, the two main areas associated with language are Broca’s area, which helps us speak, and Wernicke’s area, which helps us understand language.
    占主導地位的兩個半球內,與語言相關的兩個主要領域是Broca區,能幫助我們說話,和Wernicke區,可以幫助我們理解語言。
    Broca’s area is in the frontal lobe, usually the left frontal lobe, and it’s responsible for language expression.
    Broca區在額葉,通常由左額葉進行處理,並負責語言表達。
    When Broca’s area is damaged, people tend to have trouble producing speech.
    當Broca區損壞時,人們往往會有發音的困難。
    Their words become halting or slurred.
    他們的言語變得緩慢或含糊不清。

    This is called non-fluent aphasia, or Broca’s aphasia.
    這稱作非流利失語症或Broca’s失語症。
    I remember this by thinking that Broca’s aphasia means “ broken speech,” and aphasia is just any type of disorder that involves language.
    我記得這個被認為是Broca失語症意味著"斷斷續續的講話",失語症只是多種類型的障礙中涉及到語言。
    When Wernicke’s area, back in the temporal lobe, is damaged, you get Wernicke’s aphasia, which is quite a different pattern of behavior than you get with Broca’s aphasia.
    當在顳葉後的Wernicke區被損壞時,你會得到Wernicke區失語症,這和得到Broca區失語症所表現出來的行為有很大的不同。
    People have no trouble producing words—in fact, words kind of just tumble out of them—but the words that do come out don’t make any sense.
    他們沒有發音的困難,事實上,他們只是把那些字講出來,但那些字是沒有任何意思的。
    It’s like listening to a bunch of nonsense sentences.
    就像在聽一堆毫無意義的句子。
    People with Wernicke’s aphasia, which is also sometimes called” fluent aphasia,” can also have trouble understanding what other people say.
    有Wernicke失語症的人有時也稱作流利失語症,對於別人所說的話有理解困難。
    And when both Broca’s aphasia and Wernicke’s aphasia are present, then you have something called “global aphasia,” because it globally affects language instead of only affecting a subsection of it.
    當Broca失語症和Wernicke失語症都存在,就稱作全面性失語症,因為會有全面性的影響而非只有部分影響。
    Broca’s area and Wernicke’s area are connected in the brain by a bundle of nerve fibers called the arcuate fasciculus.
    Broca區和Wernicke區在大腦中會經由一束的弓形神經束連接。
    One cool thing is that this loop is also found in deaf people who know sign language.
    一件有趣的事是,也在懂得手語的聾子上發現了這個環節。
    So it’s not specific to a spoken language, but the brain adapts to use whatever modality is necessary for communication.
    所以,它不是特定於口語,但是大腦習慣使用必要的方式來溝通。
    When this connection is damaged, people experience something called “conduction aphasia.”
    當這個連結被破壞時,人們會經歷傳導性失語症。

    Their ability to conduct information between listening and speaking is disrupted, which makes them unable to repeat things, even though they understand what’s being said.
    他們在聽力和口語之間傳達的能力被破壞,造成他們不能複誦事情,即使他們聽得懂正在說什麼。
    Pretty crazy.
    相當瘋狂。
    And once you think about how many language-specific functions you do every day, you might wonder how many different types of aphasia there are.
    一旦你思考每天有多少特定的語言功能在運作,你將得知有多少不同種類的失語症存在。
    And the answer is “ a lot.”
    答案是很多。
    We have agraphia, which is the inability to write, anomia, which is the inability to name things, and other specific difficulties in reading, spelling, grammar, pronunciation—all sorts of things you may not even realize that you do effortlessly with a healthy brain.
    有失寫症,即沒有書寫的能力,命名失能症,即無法為事物命名,還有閱讀、拼音、文法、發音等具體的困難,各式各樣的事情,你甚至不知道你有健康的大腦不費力氣的完成這些事。
    But Broca’s apahasia and Wernicke’s aphasia are the most common.
    但是,Broca失語症和Wernicke失語症是最常見的。
    Language is just one example of how our brain works in general.
    語言只是大腦如何運作最常見的一個例子。
    Big tasks are subdivided into small tasks, which are then spread around in different parts of the brain.
    大任務被分成小任務,然後散佈在大腦不同的部位。
    And this can actually be a good thing, because it means if you have very localized or very specific brain damage, then you probably won’t completely lose your ability to perform some highly important function like communication.
    而這實際上是一件好事,因為這意味著如果你有非常局部的或非常特定的腦部損傷,那麼你可能不會完全失去你執行一些非常重要的功能,例如溝通。
    In fact, when functions are divided like that, it’s easier for your brain to adapt.
    事實上,當功能被那樣劃分,它更容易讓你的大腦適應。
    For example, when people have strokes that affect the left hemisphere of their brain, they may have trouble speaking or something right after the stroke, but over time and with proper therapy, some of those people are able to retrain other speech-related parts of their brain by creating new connections between neurons.
    例如,當人們有中風影響到左半腦,他們可能有說話障礙,或者影響到右腦,但是,隨著時間的推移和適當的治療,其中的一些人都能夠透過創建神經元之間的新連接重新訓練他們大腦其他語音相關的部分。
    Building these connections, in combination with some recovery of the originally damaged part of the brain, can help these people speak again with at least some degree of fluency.
    建立這些連接,結合一些大腦原來損壞已恢復的部分,可以幫助這些人講話時能再有至少某種程度的流暢性。
    And the brain’s ability to adapt and move functions to new parts is called neural plasticity, or synaptic plasticity.
    而大腦適應並移動新部分的功能的能力稱為神經可塑性或突觸可塑性。
    The neurons are plastic, or flexible enough, to learn new routes and connections, thus allowing undamaged parts of the brain to take over functions that the damaged parts previously performed.
    神經元是塑料,或具有足夠的靈活性,學習新的路線且連接,從而允許大腦未損壞的部分接管以前執行的受損部位的功能。
    Even with perfectly functioning hemispheres, you might still have trouble naming objects.
    即使有充分發揮功能的兩半球,你可能仍然有為物體命名的困難。
    This can happen if communication between the hemispheres is disrupted by severing the corpus callosum, which is a band of nerve fibers that connects your brain’s two hemispheres.
    這可能發生在如果胼胝體被切斷兩半球之間的溝通就會中斷,胼胝體是一堆的神經纖維用來連結大腦的兩半球。
    This creates what’s called a split-brain patient, because your brain is now split into two parts.
    這形成了所謂的腦裂患者,因為你的腦袋現在已被分成兩部分。
    People used to have to do this sometimes as a treatment for seizures, but in addition to helping with that problem, this surgery creates some pretty interesting side effects in terms of language.
    人們曾經把這一點當作治療癲癇的方法,但除了幫助這一個問題,這種手術造成語言某些有趣的副作用。
    So assuming that language is centralized in the left hemisphere, this means that the right side of your brain can’t connect to the language side.
    所以,假設語言集中在左半球,這意味著你的大腦右側無法連結到語言方面。
    So anything that you perceive in the right side of your brain can’t be named or dealt with in terms of language.
    所以任何你察覺到的事情無法被你的右側大腦命名或有語言方面的處理。
    Now, you may have heard before that your brain has what’s called a contralateral organization, meaning that information that you perceive in your left visual fied gets processed by the right side of your brain and vice-versa.
    現在,你之前可能已聽過你的大腦有個叫做對側組織的結構,意思是你左半邊的視覺區所察覺到的訊息會經由大腦右側取得處理,反之亦然。
    So let’s think about what that means for a split-brain patient.
    所以,讓我們來想想什麼是腦裂患者。
    If your see an object on your left, and it gets sent to your right hemisphere, you won’t be able to name it.
    假如你看到一個物體在你左邊,接著就會將影像傳到右半球,你不能夠為它命名。
    You’d still be able to pick it up with your left hand, because again, your right hemisphere is controlling your left-side motor neurons, but you’d have to kind of turn your head so that the object would be in your right visual field before the language part of your brain would have any access to it.
    你仍然可以把它撿起來用你的左手,因為,你的右半球控制你的左側運動神經元,但你要轉動你的頭,這樣物體將會在你的右側視野區在大腦語言區有任何連結之前。
    Now, when I say the right visual field, that doesn’t mean just your right eye.
    現在,當我說右側視野,這並不完全意味著你的右眼。
    It means the right side of your body, which you can view with half of each eye.
    意思是你的右側身你兩個眼睛都可以看。
    So there you go.
    這樣就可以了。
    Lots of pretty cool implications for how our brain is organized and subdivided in terms of language.
    有很多很酷的影響影響著我們的大腦組織和細分語言的部分。

  4. Wow, thank you so much for clarifying things and making them easier to understand. You are an excellent educator.

  5. Thank you so much for this. It has been a year since I had my stroke. Aphasia, apraxia, etc. have been very difficult for me. This video shows there are so many facets to our brain.

  6. You mentioned that damage to Broca's area can produce "slurred speech" – this is not a symptom of an aphasia, that's dysarthria. Dysarthria = motor speech, aphasia = cognition (ie language).

  7. I was given this subject as my presentation topic for my college biology class… Little did I know how fascinating this is and learned many things I wasn't aware of. Thank you for perfectly explaining it in this video!

  8. this may explain why I have trouble saying certain things or explaining myself. I've been told it's the way my brain is "wired"

  9. Can you please explain the "Model of single-word processing for auditory and written word perception and production. Including processes involved in picture naming."

    And levels of breakdown and impact?

    Pleeeeeease

  10. My stroke wiped out my ability to read! My ability to recognize letters and read them correctly was scrambled. Is there an aphasia type for that? Technology help me compensate and I'd be worse off if this stroke had happened before the appearance of tech tools to help me compensate.

  11. What are possible reasons for not being able to produce thought via speaking? My problem is being stunned or drawing complete blanks when I am supposed to talk but the words come much more vividly when I write. I am left handed, and never liked speaking. In fact, it causes me stress at times.

  12. I have a hard time thinking of what to say and how to keep convo going. I want to be able to talk like a public speaker. What could be the issue?

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