LATERALIZATION

, LANGUANGE &

SPLIT BRAIN

LATERALIZATION

Lateralization refers to the idea

that each hemisphere of the brain

is specialized for different

functions.

(Nobel-prize-winners Roger

Sperry and Robert Ornstein )

helps us to understand our behavior,

our personality, our creativity, and

our ability to use the proper mode of

thinking when performing particular

tasks

"brain dominance" -- the tendency

to act and think in the mode of either

the left or right hemisphere.

The decision is affected by our

genetics, childhood experiences,

and family environment

Tests of Cerebral Lateralization

Nearly all (about 95%) right-handed subjects are left-hemisphere dominant for speech;

most left-handed or ambidextrous subjects (about 70%) are also left-hemisphere dominant for speech;

Early left-hemisphere damage can cause the right hemisphere to become dominant for speech and the left hand to be preferred

Sex Differences and Lateralization

Some evidence suggests that the male brain is more lateralized than female brain.

e.g., McGlone’s (1977, 1980) studies of unilateral stroke victims and WAIS subscore tests

Some fMRI studies show that females tend to use both hemispheres in language-related tasks more so than males

So, if a brain functions based on

hemispheres or separate areas, what

would happen if a person lost half their

brain? Would they still be able to function?

Would they be able to survive?

-Myers and Sperry, 1953-

LANGUANGE

Broca’s Area

• In 1861, Paul Broca described a patient who could say only one word..."tan." For this reason, Broca called this patient "Tan." When Tan died, Broca examined his brain and found that there was damage to part of the left frontal cortex. This part of the brain has come to be known as "Broca's Area.“

• Broca's area (inferior frontal gyrus) is involved mostly in the production of speech, given its proximity to the motor cortex.

Wernicke's Area

• In 1876, Karl Wernicke found that damage to a different part of the brain also caused language problems. This area of the brain “Wernicke's Area", was further back and lower in the brain compared to Broca's area.

• Wernicke's area (posterior section of the superior temporal gyrus) is located relatively between the auditory cortex and the visual cortex.

APHASIA

• The acquired language disorders that are associated to brain activity are called aphasias. Depending on the location of the damage, the aphasias can present several differences.

Expressive Aphasia

• Broca's aphasia• Usually characterized as a nonfluent aphasia• Prevents a person from producing speech• Words are not properly formed• Speech is slow and slurred.• Frequently omit small words.

• Have a hard time reproducing speech• Although most of their cognitive functions

remain intact, and are still able to understand language.

• They are aware of their language disorder and may get frustrated.

Receptive Aphasia

• Wernicke's aphasia• Person can speak clearly, but the words that

are put together make no sense. This way of speaking has been called "word salad" because it appears that the words are all mixed up like the vegetables in a salad.

• Loss of the ability to understand language• Hard time understanding what others try to

communicate. • Often unaware of their mistakes.

Conduction Aphasia

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

• Damage to the arcuate fasciculus causes a disorder called conduction aphasia.

• Can understand language, but their speech does not make sense and they cannot repeat words.

Electrical Stimulation

• Early 1950s: Neurosurgeon Wilder Penfield & Herbert Jasper, described how electrical stimulation of certain areas of the brain blocked language.

• By asking their patients questions during the surgical procedure.

• Late 1980s, Dr. George Ojemann has used electrical stimulation experiments to show that there can be a large difference in the brain area that is important for language from person to person.

• The results of these studies agree with the earlier findings of Broca and Wernicke.

Wada Test

• Uses a fast acting anesthetic called sodium amytal (amobarbital)

• Put one hemisphere of the brain asleep. • The sodium amytal is injected into the right or left carotid

artery. The right artery supplies the right cerebral hemisphere and the left artery supplies the left cerebral hemisphere.

• If the left hemisphere is put to sleep in people who have language ability in the left hemisphere, then when asked to speak, they cannot. However, if the right hemisphere is put to sleep, then these people will be able to speak and answer questions

Brain Imaging Techniques

• Positron Emission Tomography (PET)• A scanner detects radioactive material that is

injected or inhaled to create an image. • Many of the expected areas of the brain have

increased blood flow during language tasks, but there are also areas on both hemispheres that are activated.

Dichotic listening

• Patients will listen to conflicting stimuli in both ears and participants have to say what they hear. If they say what they heard from the left ear, then the right brain is the language brain because dominant ear is contralateral.

SPLIT BRAIN

SPLIT BRAIN

o Severed or absence of corpus callosumeliminate the main connection between the

two hemispheres of the brain.

Agenesis : born without corpus callosumCommissurotomy : performed on patients with

life-threathening cases of epilepsy to decrease severity

i) Tachistoscope

S P L IT B RA IN EXPERIMENT

ii) Chrimeric fiqure

Two independence streams of consciousness

• When an object was presented to the left hemisphere, either by touching something with the right hand or viewing something in the right visual field, the subject could :– Pick out the correct object with the right hand– Could not pick out the correct object with the left

hand– Could name the correct object

• When an object was presented to the right hemisphere, either by touching something with the left hand or viewing something in the left visual field, the subject could:– Could pick out the correct object with the left

hand– Could not pick out the correct object with the

right hand– Claimed nothing had been presented

"The great pleasure and feeling in my right brain is more than my left brain can find the words to tell you."

Roger Sperry