Download Module 6 The Cerebral Cortex and Our Divided Brain

Structure of the Cortex
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Newer neural networks within the cerebrum form
specialized areas that enable us to perceive, think, and
speak.
Some of these areas are only 50,000 years old; that is
practically brand new in terms of evolution.
This brain area requires a lot of fuel (glucose, or bloodsugar), and myeline sheathing. This is supplied by the
glial cells. They support, nourish, and protect neurons,
and play a role in learning and thinking. For example, glial
cell death has been linked to clinical depression.
They also guide neural connections, and mop up excess
ions.
The more complex the brain, the more glial cells.
The Cerebral Cortex
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Memorize Figure 6.1: the cortex and its basic
subdivisions.
Figure 6.2 The amount of cortex devoted to a body part is
not proportional to the part's size. Rather, the brain
devotes more tissue to sensitive areas and to areas
required precise control.
Input comes through and from the sensory cortex; output
through and from the motor cortex.
Gibbs (1996) was able to predict a monkey's arm motion
a tenth of a second before it moved--by repeatedly
measuring motor cortex activity preceding specific arm
movements.
This has lead to brain-controlled computers.
Brain-Computer Interaction
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Figure 6.4: A patient with a severed spinal cord has
electrodes planted in a parietal lobe region involved with
the planning to reach one's arm.
The resulting signal can enable the patient to move a
robotic limb, stimulate muscles that activate a paralyzed
limb, navigate a wheelchair, and use the internet.
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This is only the beginning!
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Memorize Figure 6.6: The sensory cortex.
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Visual cortex = Occipital lobe.
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Most neuroscience breakthroughs began with vision
research.
Association Areas
Three quarters of the cortex is devoted to association areas.
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Electrical probing won't yield an observable response.
That has led to the misguided claim that we ordinarily
used only 10% of our brains.
Surgically lesioned animals and brain-damaged humans
bear witness that association areas are not dormant.
Figure 6.8: The Strange Case of Phineas Gage
Parietal association areas enable mathematical and
spatial reasoning.
The underside of the right temporal lobe enables us to
recognize faces, and subtle facial expressions.
Plasticity
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Our brains are sculpted not only by our genes, but by our
experiences.
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Severed neurons usually do not regenerate.
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Some brain functions seem preassigned to specific areas.
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One newborn who suffered damage to temporal lobe
facial recognition areas later remained unable to
recognize faces.
Some neural tissue can reorganize in response to
damage.
Constraint-induced therapy aims to rewire brains and
improved the dexterity of a brain-damaged child.
Damaged brain functions can migrate to other regions.
Splitting the Brain
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Memorize Figure 6.11, and look out! There is a left and
right visual field in each eye.
Sperry and Gazzaniga (1967) worked with patients who
had a severed corpus callosum, the massive network of
nerve fibres that link the two hemispheres (significantly
thicking in females).
The trick with Fig. 6.12 is to remember that the stimulus is
flashed to the subject. This means a duration of no more
than 1/2 second.
The left hemisphere did the talking, becoming
increasingly bewildered by what the non-verbal right
hemisphere knew.
Right-Left Intact Brain
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Language is language; spoken or signed. Deaf people
use the left hemisphere to process sign language.
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LH = quick, literal interpretations.
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RH excels in making inferences.
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RH helps to modulate speech to increase clarity of
meaning.
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RH helps to orchestrate our sense of self.
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Remember this 'sense of self' for Web Article Two.