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

Summary

This video script explores the brain's language functions, focusing on how we speak and understand language. It highlights that for most right-handed individuals, language is processed in the left hemisphere, with Broca's area for speech production and Wernicke's area for comprehension. Damage to these areas can result in different types of aphasia. The script also discusses the brain's adaptability, such as neural plasticity, which allows for recovery of language functions after brain damage. Additionally, it touches on the effects of a split-brain, where the disconnection of the brain's hemispheres can lead to intriguing language-related phenomena.

Takeaways

• 🧠 Language in the brain is not a single function but is divided into many sub-functions.
• 👉 For most right-handed individuals, language functions are primarily located in the left hemisphere of the brain.
• 🤲 Left-handed and ambidextrous people may have language functions in the right hemisphere, but a majority still use the left.
• 🗣️ Broca's area, in the frontal lobe, is crucial for speech production, and damage can lead to non-fluent aphasia.
• 👂 Wernicke's area, in the temporal lobe, is key for language comprehension, and its damage results in fluent aphasia.
• 🔗 The arcuate fasciculus connects Broca's and Wernicke's areas, and damage here causes conduction aphasia, affecting the repetition of speech.
• 🤝 The brain's ability to adapt is known as neural plasticity, allowing for the retraining of language functions after damage.
• 🧐 There are various types of aphasia, each affecting different aspects of language, such as writing (agraphia) or naming (anomia).
• 🧬 The corpus callosum connects the two brain hemispheres, and severing it can lead to split-brain phenomena affecting language.
• 👁️‍🗨️ In split-brain patients, the right hemisphere cannot name objects perceived in the left visual field due to the disconnection from the language center.

Q & A

In which hemisphere of the brain are language functions typically centralized for right-handed people?

For about 90% of right-handed people, language functions are centralized in the left hemisphere of the brain.

What are the two main areas associated with language within the dominant hemisphere?

The two main areas associated with language are Broca's area, which helps us speak, and Wernicke's area, which helps us understand language.

What is the effect on speech when Broca's area is damaged?

When Broca's area is damaged, people tend to have trouble producing speech, resulting in halting or slurred words, known as non-fluent aphasia or Broca's aphasia.

How does Wernicke's aphasia differ from Broca's aphasia in terms of speech production?

In Wernicke's aphasia, people have no trouble producing words, but the words that come out don't make sense, unlike Broca's aphasia where speech production is difficult.

What is the term for the condition where both Broca's and Wernicke's aphasia are present?

When both Broca's aphasia and Wernicke's aphasia are present, it is called 'global aphasia' because it affects the global use of language.

What is the bundle of nerve fibers that connects Broca's area and Wernicke's area?

Broca's area and Wernicke's area are connected by a bundle of nerve fibers called the arcuate fasciculus.

What happens when the arcuate fasciculus is damaged?

When the arcuate fasciculus is damaged, people experience conduction aphasia, which disrupts their ability to conduct information between listening and speaking, making them unable to repeat things.

What is neural plasticity and how does it relate to language recovery after brain damage?

Neural plasticity, or synaptic plasticity, is the brain's ability to adapt and move functions to new parts. It allows undamaged parts of the brain to take over functions that the damaged parts previously performed, which can help in language recovery after strokes.

What is a split-brain patient and how does it affect language?

A split-brain patient is a person whose corpus callosum, the band of nerve fibers connecting the brain's two hemispheres, has been severed. This can disrupt communication between the hemispheres, leading to difficulties in naming objects perceived by the non-dominant hemisphere.

How does the contralateral organization of the brain affect a split-brain patient's ability to name objects?

In a split-brain patient, information perceived in the left visual field gets processed by the right hemisphere, which cannot connect to the language center in the left hemisphere. This means they cannot name objects perceived in their left visual field without turning their head to bring the object into the right visual field.

What are some specific language difficulties other than aphasia that can result from brain damage?

Other specific language difficulties include agraphia (inability to write), anomia (inability to name things), and difficulties in reading, spelling, grammar, and pronunciation.

Outlines

00:00

🧠 Language and the Brain's Specialization

This paragraph delves into the neurological aspects of language processing in the brain. It explains that language is not a single function but a complex set of sub-functions, many of which are lateralized to the left hemisphere in right-handed individuals. The text introduces Broca's area, associated with speech production, and Wernicke's area, which aids in language comprehension. Damage to these areas results in distinct types of aphasia: Broca's aphasia, characterized by non-fluent speech, and Wernicke's aphasia, marked by fluent but nonsensical speech. The arcuate fasciculus, connecting these two areas, is highlighted as crucial for language transmission. The concept of neural plasticity is also introduced, showing how the brain can adapt and rewire itself to recover language functions after damage.

05:00

👁️‍🗨️ Split-Brain Phenomena and Language Processing

The second paragraph explores the effects of split-brain surgery on language capabilities. It discusses how language functions are typically centralized in the left hemisphere, leaving the right hemisphere without direct access to language processing. This results in a contralateral organization where the left visual field is processed by the right brain, and vice versa. The implications for split-brain patients are significant: they cannot name objects presented to their left visual field because the right hemisphere cannot communicate with the language-dominant left hemisphere. This leads to the need to shift visual focus to the right visual field for language processing. The paragraph provides a fascinating look into the brain's organization and the challenges faced by split-brain patients in terms of language and perception.

Keywords

💡Broca's area

Broca's area is a region in the left frontal lobe of the brain responsible for language expression. When it is damaged, people have difficulty producing speech, which is referred to as Broca's aphasia or 'non-fluent aphasia.' This area is crucial in the process of forming coherent speech, as mentioned in the video where people with damage to Broca's area have 'broken speech.'

💡Wernicke's area

Wernicke's area, located in the temporal lobe, helps with understanding language. Damage to this region results in Wernicke's aphasia, where individuals can produce fluent but nonsensical speech and have difficulty comprehending others. This is known as 'fluent aphasia.' The video highlights that people with Wernicke's aphasia can speak in sentences, but the content is nonsensical.

💡Aphasia

Aphasia refers to any disorder related to language, affecting speaking, understanding, reading, or writing. The video discusses different types of aphasia, including Broca's aphasia and Wernicke's aphasia. Aphasia arises from brain damage in language-related areas, affecting communication abilities in varied ways depending on the region of the brain impacted.

💡Arcuate fasciculus

The arcuate fasciculus is a bundle of nerve fibers connecting Broca's and Wernicke's areas, playing a crucial role in language processing. When damaged, it results in conduction aphasia, where individuals struggle to repeat words even though they understand them. The video explains how this connection enables coordination between language comprehension and expression.

💡Neuroplasticity

Neuroplasticity, or synaptic plasticity, refers to the brain's ability to adapt and reorganize by forming new neural connections. The video explains that after a stroke affecting language areas, neuroplasticity allows undamaged parts of the brain to take over some functions of damaged regions, aiding in recovery of speech abilities through therapy and new neural connections.

💡Split-brain patient

A split-brain patient is someone whose corpus callosum, the bundle of nerve fibers connecting the brain's two hemispheres, has been severed. This treatment was historically used for severe epilepsy, but it results in communication difficulties between the hemispheres, particularly in language processing. The video provides the example that if a split-brain patient sees an object in their left visual field, they cannot name it because the right hemisphere cannot communicate with the left language-dominant hemisphere.

💡Corpus callosum

The corpus callosum is the nerve fiber bundle that connects the left and right hemispheres of the brain, facilitating communication between them. The video mentions that severing the corpus callosum can lead to split-brain syndrome, disrupting functions such as naming objects perceived by the non-language-dominant hemisphere.

💡Non-fluent aphasia

Non-fluent aphasia, also called Broca's aphasia, occurs when Broca's area is damaged, resulting in halting or slurred speech. In the video, it is described as 'broken speech,' where people have difficulty producing language, though they may still understand what others are saying.

💡Fluent aphasia

Fluent aphasia, also known as Wernicke's aphasia, occurs when Wernicke's area is damaged. Individuals with fluent aphasia can speak in flowing sentences, but the content is nonsensical or jumbled, and they struggle to understand language. The video uses this example to contrast it with non-fluent aphasia, showing different language impairments based on brain damage.

💡Global aphasia

Global aphasia is a severe form of aphasia where both Broca's and Wernicke's areas are damaged, affecting all aspects of language, including speaking, understanding, reading, and writing. The video explains that global aphasia occurs when language functions are globally disrupted across multiple regions of the brain.

Highlights

Language functions are divided into sub-functions in the brain.

90% of right-handed people have language functions in the left hemisphere.

About 70% of left-handed and ambidextrous people have language in the left hemisphere.

Broca's area, in the frontal lobe, is crucial for speech production.

Wernicke's area, in the temporal lobe, is essential for language comprehension.

Damage to Broca's area results in non-fluent aphasia, characterized by slurred speech.

Wernicke's aphasia is marked by fluent but nonsensical speech and comprehension difficulties.

Global aphasia affects both speech production and comprehension.

The arcuate fasciculus connects Broca's and Wernicke's areas, facilitating language processing.

Sign language users also have a developed arcuate fasciculus, showing brain adaptability.

Conduction aphasia occurs when the arcuate fasciculus is damaged, affecting speech repetition.

There are many types of aphasia, including agraphia and anomia.

The brain's ability to adapt and retrain after damage is known as neural plasticity.

Split-brain patients have severed corpus callosum, affecting interhemispheric communication.

In split-brain patients, the right hemisphere cannot name objects perceived in the left visual field.

The contralateral organization of the brain means the left visual field is processed by the right hemisphere.

Split-brain patients must adjust their visual field to access language functions for object naming.

Transcripts

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.