Transcript Document

Biological Psychology – Mod. 3 & 4
The Split-Brain Phenomenon
Left-handedness
Synaptic Plasticity
Biomedical Therapies
General Psychology 1
February 15, 2005
Class #7
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
Left Handedness: Curse or Blessing
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Around ten percent of Americans are
left-handed, and of those, there are
twice as many lefty males as females
A curse???
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Possible disadvantages
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Medical literature reports that lefties are more
accident prone…Lefties are six times likelier to
die in an accident, and four times likelier to die
while driving
For example: they are more likely to have their
fingers amputated by power-tools, suffer more
wrist fractures (Corliss, 1984)
Lefties are more susceptible to allergies,
reading disabilities, and migraine headaches
(Geschwind and Behan, 1984)
Or a blessing???
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Possible advantages
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Lefties are more common among professional
baseball and cricket players, architects and
artists
Corpus callosum is about 11% greater in lefthanders…
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Leading to greater integration of both brain
hemispheres in processing information
The Effects of the Brain on
Handedness: Some Theories
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Damage to the brain, an insufficient
supply of oxygen to the brain, and a
difficult birth are thought to cause lefthandedness…
 This theory has been accepted by many, as
the number of lefties who fall under these
categories is surprisingly high
 An unusually high percentage of mentally
retarded children are left-handed
The Effects of the Brain on
Handedness: Some Theories
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Twins are notorious for having difficult
births, and have a high rate of lefthandedness too...about 20%, which is
twice the normal rate
It is also thought that the tendency to
have difficult births is genetic, which
would back up the statistics for lefthandedness to run in the family
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
Example: Professor at Iona College – a stroke
victim
 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
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Illustrates that the brain has extraordinary powers of reorganization,
especially when damaged before it is fully developed
Plasticity vs. split-brain
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So, if you have a split-brain operation
there is no sharing of information
Yet, if you remove one side of the brain at
an early age you will see synaptic
plasticity take place and he/she will likely
live a normal life
Biomedical Therapies
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Psychosurgery
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Lobotomies
Electroconvulsive Therapy (ECT)
Drug Therapies
Psychosurgery
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This is one type of treatment used for
some of the most devastating
psychological disorders (like
schizophrenia) in which surgery is
performed that removes or destroys brain
tissue in an effort to change behavior
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This is a drastic biomedical intervention
A last resort operation
Lobotomies
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Egas Moniz (1935)
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Developed the best known psychosurgical
operation – the lobotomy
Moniz found that when he surgically cut the
nerves that connect the frontal lobes with the
emotion-controlling centers of the inner brain,
uncontrollably emotional and violent patients
were calmed
His hope was to disconnect emotion from
thought
Lobotomies
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During the 1940’s and 1950’s around
50,000 or more severely disturbed
individuals were “lobotomized” and Moniz
was honored with a Nobel Prize
Some of his patients are still alive today
Lobotomies
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At first, his procedure was welcomed by the
medical community…
 Immediate relief from emotional anguish
Unfortunately, the side effects were drastic…
 Although, intellect appeared virtually
unaffected – these patients showed serious
changes in their personality
 Becoming irresponsible and childish
Lobotomies
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They lost the ability to carry out plans and most
became unemployed
The lobotomy had produced a permanently
lethargic and immature personality
So, although the pathological emotional
problems had been eliminated – so too had the
normal aspects of that person’s personality
No longer performed…
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Lobotomies are no longer performed for
obvious reasons…
Electroconvulsive Therapy (ECT)
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This is the controversial practice of
“shock” treatment
A less-drastic manipulation of the brain
than psychosurgery
First introduced in 1938
Early treatments…
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A wide-awake person was strapped to a
table and jolted with about 100 volts of
electricity to the brain
Produced violent convulsions and
momentary unconsciousness
Convulsions sometimes caused injury
Separated shoulders, etc.
Today…
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Its done differently as the patient is given
a general anesthetic and muscle relaxant
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See video clip
Used primarily to treat severely depressed
individuals, schizophrenics, OCD sufferers,
etc.
Only used after drug treatments have
been unsuccessful
Drug Therapies
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By far the most widely used biomedical
treatment…
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They were introduced in 1950’s and have
greatly reduced the need for hospitalization
Antipsychotic, antianxiety, and antidepressant
drugs have been used effectively to help calm
individuals, reduce emotional stress in people
and lift the spirits of the clinically depressed
Effectiveness???
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Drugs such as antianxiety drugs and
antidepresants are not a cure…but they do
reduce the symptoms and help a person
function…
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See video clip