Read more, Understand more! Lateralization, Language & Split Brain

2. LATERALIZATION

3. Lateralization refers to the idea that each
hemisphere of the brain is specialized for
different functions.
(Nobel-prize-winners Roger
Sperry and Robert Ornstein )

5.  helps us to understand our behavior, our
personality, our creativity, and our ability
to use the proper mode of thinking when
performing particular tasks

6.  "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

7. 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

8. 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

9. 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-

10. LANGUANGE

11. 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.

12. 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.

14. APHASIA

15. • 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.

16. 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.

17. • 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.

18. 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.

19. • Loss of the ability to understand language
• Hard time understanding what others try to
communicate.
• Often unaware of their mistakes.

20. 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.

22. 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.

23. 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

24. 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.

25. 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.

26. SPLIT BRAIN

27. SPLIT BRAIN

28. o Severed or absence of corpus callosum
eliminate the main connection between the
two hemispheres of the brain.
Agenesis : born without corpus callosum
Commissurotomy : performed on patients with
life-threathening cases of epilepsy to decrease
severity

29. i) Tachistoscope
SPL IT BRAIN EXPERIMENT

30. ii) Chrimeric fiqure

31. 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

32. • 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

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