Parietal Lobe | Cerebral Cortex

Summary

In this educational video, Dr. Mike explores the parietal lobe, the sensory cortex of the brain. He explains its role in processing tactile information, including touch, proprioception, temperature, and pain, through the sensory homunculus map. The video delves into the anatomical margins, the postcentral gyrus, and the concept of neuroplasticity, highlighting how the brain adapts when a limb is lost. It also covers the association cortex's role in identifying objects and understanding speech, with a focus on the supramarginal and angular gyri, which are crucial for empathy and language processing.

Takeaways

• 🧠 The parietal lobe is the sensory cortex of the brain, responsible for processing information from the senses.
• 👂 It is crucial for understanding tactile information such as touch, proprioception, temperature, and pain.
• 📏 The postcentral gyrus in the parietal lobe contains a sensory homunculus, a map of the body's areas that can feel sensation.
• 🔍 The sensory homunculus does not represent the body in a typical order, with some areas like the hand and lips enlarged due to their sensitivity.
• 🤲 The hand and lips have a high degree of two-point discrimination, indicating a dense concentration of sensory neurons.
• 🧩 Neuroplasticity allows the brain to adapt when a limb is lost, with sensory neurons of the missing limb 'talking' to neighboring neurons, such as those of the face.
• 🔑 The somatosensory cortex helps in judging the size, weight, and texture of objects through touch.
• 🧠 The association cortex integrates information from various brain areas to identify objects and understand experiences.
• 🤝 The supramarginal gyrus is involved in understanding posture and position, both of oneself and others, and plays a role in empathy.
• 🗣️ The angular gyrus is essential for word choice and has a connection with Wernicke's area, which is important for understanding speech and written text.
• 🔍 Damage to the association cortex can lead to difficulty in identifying objects, while damage to Wernicke's area can affect the understanding of speech and written text.

Q & A

What are the four main lobes of the brain?

The four main lobes of the brain are the frontal lobe, parietal lobe, occipital lobe, and temporal lobe.

What is the primary function of the parietal lobe?

The primary function of the parietal lobe is to act as the sensory cortex, processing information related to touch, proprioception, temperature, and pain.

What is the significance of the postcentral gyrus in the parietal lobe?

The postcentral gyrus in the parietal lobe contains a sensory homunculus, which is a map of the body's areas that can feel sensation.

What is the term used to describe the body's sensory map in the brain?

The term used to describe the body's sensory map in the brain is the sensory homunculus.

Why are some areas of the sensory homunculus larger than others?

Some areas of the sensory homunculus are larger because they correspond to parts of the body that have a higher concentration of sensory neurons, such as the hands and lips.

What is meant by two-point discrimination in the context of the sensory cortex?

Two-point discrimination refers to the ability to feel two separate points of contact on the skin and distinguish them as distinct from one another.

What is neuroplasticity and how does it relate to the sensory cortex?

Neuroplasticity is the brain's ability to adapt and change by forming new neural connections throughout life. It relates to the sensory cortex in cases where, for example, a limb is lost, and the brain's sensory map reorganizes to incorporate neighboring areas.

What is the role of the association cortex in the context of the parietal lobe?

The association cortex in the parietal lobe integrates information from various brain areas to help identify and understand the nature of sensory experiences, such as recognizing objects by touch.

What does the supramarginal gyrus contribute to in terms of social interaction?

The supramarginal gyrus contributes to understanding posture and position, not only of oneself but also of others, which is important for interpreting intentions and demonstrating empathy.

How is the angular gyrus related to language processing?

The angular gyrus is important for word choice and has a close relationship with Wernicke's area, which is crucial for understanding speech and written text.

What happens if there is damage to Wernicke's area?

Damage to Wernicke's area can result in difficulty understanding speech and written text, even though the individual may still be able to produce speech.

Outlines

00:00

🧠 Parietal Lobe: Sensory Cortex and Somatosensory Homunculus

The first paragraph introduces the parietal lobe, emphasizing its role as the sensory cortex. It explains the function of the postcentral gyrus, which contains the sensory homunculus—a map of the body's areas that can feel sensation, including touch, pressure, pain, and temperature. The homunculus is not organized in the same order as the body, with certain areas like the hands and lips being disproportionately large due to their heightened sensitivity. The paragraph also discusses the concept of two-point discrimination, which varies across the body, and the implications of this for the somatosensory cortex's representation of different body parts.

05:01

🔄 Neuroplasticity and Sensory Reorganization Post-Amputation

The second paragraph delves into the phenomenon of neuroplasticity, particularly in individuals who have lost a limb. It describes how the sensory neurons that once mapped the missing hand now lack stimulation, leading to a reorganization where these neurons begin to interact with neighboring neurons, such as those of the face. This can result in the experience of sensations in the missing limb when touching the face, illustrating the brain's adaptability and its ability to reassign functions in response to sensory deprivation.

10:03

🗣️ Association Cortex: Object Identification and Language Processing

The third paragraph explores the role of the association cortex in the parietal lobe, which integrates information from various brain areas to identify objects based on sensory input. It discusses the involvement of the supramarginal gyrus in understanding posture and position, both one's own and others', and its link to empathy and the mirror neuron system. Additionally, the angular gyrus's role in word choice and its connection to Wernicke's area for speech comprehension is highlighted, emphasizing the parietal lobe's broader involvement in sensory integration and higher cognitive functions.

Keywords

💡Parietal Lobe

The parietal lobe is one of the four main lobes of the cerebral cortex in the brain, situated near the top and back of the head. It is the focus of the video and is described as the sensory cortex, responsible for processing information related to touch, proprioception, temperature, and pain. The script explains its importance in understanding tactile information and its anatomical location in relation to other brain regions.

💡Sensory Cortex

The sensory cortex, specifically the somatosensory cortex in the parietal lobe, is the area of the brain that processes sensory information from the body and the environment. The video script describes it as the region where the understanding of tactile information such as touch, pressure, and pain is processed, emphasizing its role in the body's sensory perception.

💡Postcentral Gyrus

The postcentral gyrus is a region in the parietal lobe that contains the sensory homunculus, a map of the body representing areas that can feel sensation. The script explains that this gyrus is responsible for processing fine touch, two-point discrimination, proprioception, pressure, and pain, illustrating its importance in sensory perception.

💡Sensory Homunculus

The sensory homunculus is a representation of the body within the somatosensory cortex, showing the areas responsible for different types of sensation. The video script uses the sensory homunculus to illustrate how certain body parts, like the hands and lips, have larger representations due to their heightened sensitivity to touch and pressure.

💡Two-Point Discrimination

Two-point discrimination is a test of tactile sensitivity, where a person's ability to discern two separate points of contact on the skin is measured. The script provides an example of this concept, explaining how the sensitivity of the hand allows for fine two-point discrimination, while the back has a much larger threshold.

💡Neuroplasticity

Neuroplasticity, also known as brain plasticity, is the brain's ability to change and adapt as a result of experience. The script discusses how, in individuals who have lost a limb, the sensory neurons previously associated with the hand can adapt and start to respond to stimuli on the face, demonstrating the brain's capacity for reorganization.

💡Association Cortex

The association cortex integrates information from various sensory modalities to form a comprehensive understanding of the environment. The video script explains its role in identifying objects based on sensory input, combining information from the somatosensory cortex with past experiences and other brain areas to recognize what is being touched.

💡Supramarginal Gyrus

The supramarginal gyrus is part of the association cortex in the parietal lobe and plays a role in understanding posture and position, both of oneself and others. The script highlights its importance in the mirror neuron system, which allows for the interpretation of others' intentions and postures, and its connection to empathy.

💡Angular Gyrus

The angular gyrus, another part of the association cortex, is involved in language processing, particularly word choice. The script explains its connection to Wernicke's area, which is crucial for understanding speech and written text, and how the angular gyrus aids in selecting the appropriate words to express thoughts.

💡Wernicke's Area

Wernicke's area, named after the neurologist Carl Wernicke, is involved in the comprehension of speech and written language. The script describes its role in understanding language and how damage to this area can result in difficulty understanding spoken or written words, despite the ability to produce speech.

💡Proprioception

Proprioception is the sense of the relative position of one's own parts of the body and the strength of effort being employed in movement. The script explains that the parietal lobe, particularly the supramarginal gyrus, is involved in proprioception, which is essential for knowing where your body parts are without needing to see them.

Highlights

The parietal lobe is the sensory cortex, playing a crucial role in understanding tactile information, touch, proprioception, temperature, and pain.

The postcentral gyrus contains a sensory homunculus, a map of the body's areas that can feel sensation.

The sensory homunculus is not in the order of the body's physical layout, with some areas like the hand and lips enlarged due to their sensitivity.

Two-point discrimination tests the ability to feel two separate points, with the hand showing the highest sensitivity.

Neuroplasticity allows the brain to adapt when a limb is lost, with sensory neurons of the missing limb beginning to interact with neighboring neurons.

The association cortex helps identify objects by integrating information from various brain areas and past experiences.

Damage to the association cortex can make it difficult to identify objects, despite understanding their tactile properties.

The supramarginal gyrus is involved in understanding posture and position, both of one's own body and others, which is crucial for empathy.

The angular gyrus assists with word choice and is closely related to Wernicke's area, which is important for understanding speech and written text.

Wernicke's area, when damaged, can lead to difficulties in understanding speech and written text, despite the ability to produce speech.

The somatosensory cortex is responsible for processing touch, pressure, pain, temperature, and proprioception.

The parietal lobe's role in sensory processing is essential for making judgments about the size, weight, and texture of objects.

The primary motor cortex and somatosensory cortex are adjacent, with the hand's sensory representation mapped next to the face.

Mirror neurons in the supramarginal gyrus allow us to understand the motivations and intentions of others through their posture and position.

Damage to the supramarginal gyrus can result in difficulties demonstrating empathy due to its role in understanding others' postures.

The angular gyrus's role in language extends to aiding in the selection of appropriate words for communication.

The parietal lobe's function in sensory processing is integral to our overall understanding of the environment and our body's interaction within it.

Transcripts

hi everybody dr mike here in this video

we're going to take a look at the

parietal lobe

now as a quick run through remember the

four main lobes include

the frontal lobe the parietal lobe the

occipital lobe and the temporal lobe

there's also the insular

which sits just sort of underneath the

temporal lobe it's like the ground floor

of the cerebral cortex now we're going

to focus on in this video

the parietal lobe which is sitting here

now when we have a look at the parietal

lobe the way you should think about it

is it is the sensory cortex now think

about when we spoke about the frontal

lobe

it's the motor cortex the action area

the

parietal lobe is the sensory cortex this

is where we get

an understanding of the things that we

are experiencing

in our body and also in the environment

around us

so it's important when it comes to

understanding tactile information

touch for example it could be touch

proprioception

temperature and pain this is where we

understand it again in the parietal lobe

but first we need to talk about the

anatomical margins that you should be

aware of remember

that we have right here an area called

the central

sulcus now central

sulcus central because it's right in the

middle

sulcus because it's a dip down and i've

spoken about the fact that when there's

a dip down either side you're going to

have a bump

up so dip down being a sulcus a bump up

is called

a gyrus now with the frontal lobe here

we've got the pre-central

gyrus and therefore here for the

parietal lobe it's called the post

central gyrus when we spoke about the

frontal lobe we said that the

pre-central gyrus

was the primary motor cortex this has

a map of the body on it of all the

muscles that we can consciously move

now the postcentral gyrus here of the

parietal lobe

has also a map of the body of areas that

can feel sensation

areas i can feel fine touch two-point

discrimination proprioception

pressure pain temperature all those

things we have a map of the body

right here and it's called our sensory

homunculus

and i've drawn it up here it looks very

similar to that of the primary motor

cortex

in which we have genitalia feet

legs bum back neck head

arm hand face lips tongue

pharynx and larynx now importantly

you can see that even though it's a map

of the body it's not really in the order

and fashion that we

see the body in and also some areas are

enlarged areas for example like the hand

and the lips why is this the case it's

because

we have the very sensitive areas right

so

when we look at the hand for example

there's a large amount of sensory

neurons in the hand

therefore there needs to be a larger

area of the brain

or the somatosensory cortex dedicated to

it

same for the lips if you think about

two-point discrimination

two-point discrimination is if you get

two points now they could be

sharp pencils they could be pinpricks

they could be whatever it may be

and if you put these two points get

somebody get them to close their eyes

and put it in an area of the body and

you ask them can you feel

two separate points and they'll say yes

i can or no i can't and you move them

closer together so

then you get them like this and say can

you discern that there's two points

now you'll find that on the hand the

two-point discrimination

is millimeters even smaller than that

before they go no it feels like only one

object but on the back

it's centimeters you could probably

place

two points this far apart on somebody's

back and say

does this feel like one object or two

and they'll probably go yeah it feels

like one object

now have a look the back has a very

small area of the somatosensory cortex

is dedicated

to it so there's not many neurons there

for sensation

but for the hand it's huge and same for

the lips it's huge large areas

dedicated to it so anytime these areas

have some sensation

right it's going to be sent up to

this area called the somatosensory

cortex which is in the post

central gyrus and just to reiterate what

we are getting here

is touch

pressure pain

temperature and proprioception do you

remember what proprioception is

proprioception is knowing your posture

and position so knowing if i close my

eyes that my arm is out here i know

where it is if i can touch my nose with

my eyes closed the reason why i can do

it is because i know where i am in my

own space i know that my arm is out here

bends at a particular angle at a

particular position because

we've got various types of receptors in

our joints muscles and areas like that

that tell us where we are in our space

that's proprioception

okay another really important point here

is that you can see that

unlike the body the hand for the

somatosensory cortex is mapped

right next to the face now the reason

why this is important is because

there's some individuals who lose a limb

now if this limb is lost let's think

about it they lose their limb at the

elbow

that hand no longer exists so the

sensory neurons in the hand

no longer exist but

the neurons dedicated to having a map of

the hand

on the brain right here they still exist

but they're not receiving

any information because the hand doesn't

exist there's nothing to stimulate the

receptors here

to send the signal down the arm into the

spine up to the thalamus

and then project it from the thalamus to

the hand and say hey

you're feeling something so these

neurons get starved of information

now the brain loves sensory information

and it doesn't want to be starved

of input so this is where a term called

neuroplasticity comes into play

the neurons of the hand start to have a

conversation with their neighbors and

what's their neighboring neurons those

of the face

right and so what that can mean is

for some individuals who have lost a

limb you can tell them to close their

eyes and you can touch their face and

say

what do you feel now think about it

you're touching the face sends a signal

in

and it goes to this area and it's

stimulating these neurons

and he goes oh i'm feeling you touch my

face but because they're now having

conversations with neurons of these

starved

hand area they can also say but now i

feel you touching my

index finger ring finger and pinky

finger

because there's a conversation being had

and that is neuroplasticity

amazing now it doesn't happen with all

people who've lost a limb but it does

happen with a subset of individuals

so when we look at the somatosensory

cortex last for us to understand

that we are feeling something touch

pressure pain temperature proprioception

whatever it may be

now in addition to that it allows for us

to make a judgment

of what we're feeling as well so it

tells us

whether it tells us basically the size

of an object the weight

of an object the texture

of an object so it does tell us this

information

but it still doesn't actually tell us

what the object

is this is where we need to bring the

next area

called the association cortex now first

let's just highlight here this

is our somatosensory cortex moving down

like that

we now need to talk about the

association cortex and the association

cortex

is sitting around about here and what

the association cortex does similar to

that

of the association cortex of the motor

cortex

is it brings in information from other

areas of the brain

and brings in previous experience to

tell you exactly what's happening

so in this scenario let's just think i

put my hand in my pocket and there's a

coin in there

so i'm feeling that coin

i'm feeling it through touch the

temperature of the coin

for example its size its weight its

texture all of this information is going

to a primary motor cortex but i don't

know it's a coin

now what the association cortex does is

it takes

information from the thalamus a deep

area of the brain

which projects up takes area from the

visual cortex

brings it back up takes area from the

auditory cortex

and brings it up and takes information

from all these other areas of the brain

to tell me what this object is so if i

take it out and look at it

visual information coming up i see it

past experience and understanding i can

say

i've felt something like this before

i've seen it before

this is a coin and that's what the

association cortex does

allows you to identify that object all

right

so if you have damage to that area it's

hard to identify what things are whether

that is a shoe

or a lamp for example or a coin but you

can still understand

the various aspects of that object

through the primary motor cortex so

that's what the association

cortex does it allows for you to

identify

objects now importantly

there's some other areas of the

association cortex that you need to be

aware of

and these areas

there's another sulcus that sits here

for example

and there's going to be another gyrus

here and another gyrus here

now these areas are important they're

part of the association cortex

this one here is called the supra

marginal gyrus

and this one here is called the angular

gyrus now again these two

are part of the association cortex now

what they importantly do super marginal

gyrus is important for telling you

about your posture and your position so

posture and position so let's write that

down

supramarginal i'll just write supra

marginal is important for posture

and position now what's posture and

position posture and position

is proprioception right so the super

marginal draft tells you about

proprioception but here's the really

cool thing

it's not just your posture and position

it's other people's posture and position

so you can actually see that by the way

somebody holds themselves

and presents themself whether that

individual is a threat

or maybe they're there to help you or

whether it's a kind

act or whether it's potentially

malicious act

now what this is telling us is it's part

of the mirror

neuron system mirror neurons allow for

us to understand

the motivations and intent of another

person therefore the super marginal

gyrus is not just important for your

proprioception posture

and position but other people's

posturing position and whether it's a

threat and this is important for

demonstrating

empathy if somebody is showing you a

kind posture

you may want to reciprocate that kind

posture and if they're showing you maybe

a not so kind posture you may want to

reciprocate that as well

therefore we know this because if

there's damage to the supramarginal

gyrus people have problems demonstrating

empathy all right so now we look at the

angular

gyrus here

and the angular gyrus is important for

word choice

it's important for word choice because

it actually

brings information down to an area right

here

called wenikki's area or wernicke's area

so right here there is an area called

wernicke's area obviously named after

somebody called

wernicke or vernicki you can see that

wernicke's area is actually not just

part of the parietal lobe but also part

of the temporal lobe as well so

some people discuss it when they talk

about the temporal lobe but let's just

talk about it here for the parietal

it is important when it comes to

recognizing

and interpreting speech and written text

so recognizing recognizing

and interpreting

written

text and speech

so it's basically seen as our speech

production

area so if there's damage to wernicke's

area the individual may have a problem

with

producing speech now they don't have a

problem are so not producing speech

with interpreting speech let me just

revise that wernicke's area is important

when it comes to understanding speech

understanding written text so they may

not be able to read what's in front of

them

but they still understand those words

brocker's area which i've spoken about

before

is a problem with speech production so

they can understand what they read but

they can't produce speech

this is the opposite they can produce

speech but they can't

understand it all right so again it has

a close relationship with the angular

gyrus which helps with word

choice okay so what we've gone through

for the parietal lobe is that it's the

sensory cortex or the sensory lobe

we've got the primary somatosensory or

the somatosensory cortex here

which has a map of the body called the

sensory homunculus

on it it's important because if we want

to understand the touch

pressure pain whatever it may be about

that tactile experience

we get that information going straight

here right via the thalamus

go straight to the somatosensory cortex

if we want to understand

more deeper detailed information about

what we are experiencing

we need to bring in the association

cortex and that includes that of the

supramarginal gyrus

and angular gyrus super marginal gyrus

is about posture and position

not just of yourself but of others and

therefore plays a role in empathy and

angular gyrus when it comes to language

and word choice

has a close relationship without a

wernicke's area which is important

with trying to understand and interpret

written speech

or auditory speech that is

a run through from the parietal lobe