Transcript Document

Biological Psychology – Module 4
The Split-Brain Phenomenon
Synaptic Plasticity
Intro Psych
Feb 12-19, 2010
Classes #11-13
The Split-Brain Phenomenon
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Corpus Callosum
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The two sides of our brains serve different
functions (lateralized or specialization of tasks):
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Large band of neural fibers that connects the two
brain hemispheres
Left hemisphere: Language, math, logic
Right hemisphere: spatial abilities, face recognition,
visual imagery, musical and artistic abilities, emotional
tasks.
This is the case for almost all righthanders
(about 95%) and about half of lefthanders
Important aspects of this divided
brain phenomenon
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Information from left half of field of vision is
received only by your right hemisphere, and
information from the right half of your field of
vision is received only by your left hemisphere
Don’t get confused here as each eye receives
sensory information from both right and left
visual fields. But this information is only
transmitted from a particular visual field to a
particular brain hemisphere
Important aspects of this divided
brain phenomenon
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The left hemisphere receives information
from and controls movements of the right
side of the body, whereas the right
hemisphere receives input from and
controls movements of the left side of the
body
Tests show that almost all right-handers
(over 95%) process speech in the left
hemisphere
Important aspects of this divided
brain phenomenon
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Left-handers are more diverse:
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60% process speech in the left hemisphere
5% process speech in the right hemisphere
35% use both hemispheres about equally
(half of the time)
Split-Brain Experiments
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Vogel and Bogen (1961)
Sperry and Gazzaniga
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Conducted many experiments from 1960’s
through the 1980’s
The Split-Brain Phenomenon
LEFT
FIELD OF VISION
RIGHT
When the patient is
asked
“What do you see?”
They answer…
LEFT
HEMISPHERE
RIGHT
The Split-Brain Phenomenon
LEFT
FIELD OF VISION
RIGHT
When the patient is asked
“What do you see?”
They answer…
LEFT
HEMISPHERE
RIGHT
The Split-Brain Phenomenon
RIGHT
LEF
T
FIELD OF VISION
The same patient who
has just said they could
not see the picture is now
asked to take their left
hand and touch the
‘happy face” picture…
What happens now???
LEF
T
HEMISPHERE
RIGHT
The Split-Brain Phenomenon
RIGHT
LEF
T
FIELD OF VISION
Now, with the object in the
patient’s hand, he/she is
asked “what is in your
hand”…what is their
answer this time???
LEF
T
HEMISPHERE
RIGHT
Severed Corpus Collusom:
Video
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1st scene:
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“Joe” is flashed words in his right field of vision
(“storm” and “piano”) and has no trouble saying them
He is then flashed the word “phone” in the left field of
vision…and he can’t say it
“didn’t see that”
But when asked to draw a picture of what he saw
with his left hand…he draws a telephone but since its
still in his left field of vision he still can’t verbalize
what he just drew
Severed Corpus Callosum:
Video
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But then when asked to draw it with his
left hand but in his right field of vision…he
is able to say what he drew (“oh, phone”)
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Very interesting…
Severed Corpus Collusom:
Video
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2nd scene:
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Joe is flashed words simultaneously in both
fields of vision – “toad” in left field and “stool”
in right field…
He can’t say “toad” but can draw it with left
hand
He can say ‘stool” and by speaking it, he is
able to let the right hemisphere in on the
“secret”
Severed Corpus Collusom:
Video
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3rd scene:
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Again, two words simultaneously…”bell”
appears in his left field of vision and “music”
in his right field of vision
When asked to point with his left hand to
what he saw, Joe points to a picture of a bell
but is not really sure why so he makes up a
story that seems to be plausible…he’s
basically trying to figure out what's going on
Severed Corpus Callosum :
Video
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Joe’s left hemisphere is trying to interpret
what is going on – trying to find a cause
and effect
Left hemisphere is responsible for making
sense out of the mystery
According to Gazzaniga: “the left
hemisphere is where the action is”…
Severed Corpus Callosum :
Video
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Final scene:
Pictures are shown of faces made out of
fruit, meat, etc.
Right hemisphere specializes in locating
faces and left is better at finding elements
involved…
So what happens?
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Right hemisphere sees it as a face and left
hemisphere sees it as a fruit
Still being performed but now very rare
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Cutting apart the two hemispheres of the human
brain is a drastic step, and it is one of the most
controversial operations ever performed
Yet it can succeed, when all else fails, in
relieving violent, drug-resistant epileptic seizures
This surgery is becoming more and more rare –
Instead, neurosurgeons are using a variety of
neuroscience techniques to reduce the amount
of tissue removed in brain surgery
Hardly ever performed now because also
because of new and effective medications that
help prevent seizures
Brain Reorganization:
Synaptic Plasticity
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Synaptic Plasticity
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Often when one area of the brain is damaged,
other areas may in time reorganize and take
over its function
 It is not uncommon for stroke patients who
have lost the ability to speak or to move a
limb to regain function after several weeks
of convalescence
How does the brain recover?
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Essentially what is occurring is a
“remodeling” of the cerebral cortex after
an injury in which sometimes a large part
of it simply dies
Of course, this is the exception and not
the rule
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Not all stroke victims recover
Even better chances: Plasticity in children
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Before the functions of young children’s cortical regions
become fixed, their brains are especially plastic…if the
speech areas of an infant’s left hemisphere are
damaged, the right hemisphere will usually take over
with no noticeable impairment of language…
 Left hemisphere damage does not permanently
disrupt language until age 8
 Case study: see hand-out
 Illustrates that the brain has extraordinary powers
of reorganization, especially when damaged before
it is fully developed