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Brain Hemispheres
Left Hemisphere |
How many brains do you have - one or two? Actually, this is
quite easy to answer...you have only one brain. However, the cerebral
hemispheres are divided right down the
middle into a right hemisphere and a left hemisphere. Each hemisphere
appears to be specialized for some behaviors. The hemispheres communicate
with each other through a thick band of 200-250 million nerve fibers
called the corpus
callosum. (A smaller band of nerve fibers called the
anterior commissure also connects parts of the cerebral
hemispheres.) |
Right
Hemisphere |
Handedness  Are you right-handed or left-handed? As you probably know,
most people (about 90% of the population) are right-handed - they prefer
to use their right hand to write, eat and throw a ball. Another way to
refer to people who use their right hand is to say that they are "right
hand dominant." It follows that most of the other
10% of the population is left-handed or "left hand dominant." There are
few people who use each hand equally; they are "ambidextrous." (Most
people also have a dominant eye and dominant ear...)
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Broca's Area
Wernicke's Area
Images courtesy of Slice of
Life.
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Right & Left Side
The right side of the brain controls
muscles on the left side of the body and the left side of the brain
controls muscles on the right side of the body. Also, in general, sensory
information from the left side of the body crosses over to the right side
of the brain and information from the right side of the body crosses over
to the left side of the brain. Therefore, damage to one side of the brain
will affect the opposite side of the body.
In 95% of right-handers, the left side of the brain is dominant for
language. Even in 60-70% of left-handers, the left side of brain is used
for language. Back in the 1860s and 1870s, two neurologists Paul Broca
and Karl
Wernicke observed that people who had damage to a particular area on
the left side of the brain had speech and language
problems. People with damage to these areas on the right side usually did
not have any language problems. The two language areas of the brain that
are important for language now bear their names: Broca's area and
Wernicke's area. |
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Left
Hemisphere
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Cerebral
Dominance
Each hemisphere of the brain is dominant
for other behaviors. For example, it appears that the right brain is
dominant for spatial abilities, face recognition, visual imagery and
music. The left brain may be more dominant for calculations, math and
logical abilities. Of course, these are generalizations and in normal
people, the two hemispheres work together, are connected, and share
information through the corpus callosum. Much of what we know about the
right and left hemispheres comes from studies in people who have had the
corpus callosum split - this surgical operation isolates most of the right
hemisphere from the left hemisphere. This type of surgery is performed in
patients suffering from epilepsy.
The corpus callosum is cut to prevent the spread of the "epileptic
seizure" from one hemisphere to the other. |
Hemisphere
- Spatial abilities
- Face recognition
- Visual imagery
- Music
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