The brainstem
"The brain stem--the small region of the
central nervous system between the spinal cord and the diencephalon--has
a clinical significance that is far out of proportion to its
size. Damage to the brain stem can profoundly affect motor and
sensory processes as well as consciousness."
[Principles of Neural Science, by Eric
R. Kandel (Editor), James H. Schwartz (Editor), Thomas M. Jessell;
Copyright 2000, The McGraw-Hill Companies, Inc.]
The brain stem is just a small area of the
brain, but it has the major collection of cells which control
awareness and behavior. All the cranial nerves (auditory, facial,
etc.) rise from groups of cells in the back of the brain stem.
These nerves control all functions in the face and the neck and
the head itself (including the rest of the brain). This area
of the brain is very tiny, and very old. It is the basis for
the evolutionary brain in humans coming from apes and back. All
animals have a brainstem...even if they do not have much else.
A child can be born with just a brain stem. These children are
called anaencephalic. They have awareness of a type, they usually
do not live long, but I have a niece who is anaencephalic. We
love her very much...she is almost nine years old. She cannot
see, but we think she hears some because of her reaction to music.
Her body controls her breathing and all other necessary functions
for life...even if she is not capable of 'thinking' as we know
thinking.
All the tracts of nerves for the body run
through this area of the brain. They know that lesions (damage,
holes, strokes) to this area of the brain can have multiple consequences
on both the motor and sensation functions of the brain. They
are starting to understand this more as they research it. Unfortunately,
understanding this part of the brain means they have to usually
cause lesions in animals (usually rats) to find out which part
of the body is affected.
--- Karen Sadler
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What is an ABI?
QUESTION:
Would someone tell me what an ABI is? I have not a clue.
ANSWER:
You understand what a cochlear implant is? An electronic device
implanted under the skin behind and above the ear with electrodes
inserted into the cochlea of a person with nerve deafness. Using
an external electronic device known as a speech processor, the
hearing nerve in the cochlea is electrically stimulated, carrying
impulses to the brain that are interpreted as sound, giving persons
with nerve deafness the ability to perceive and understand speech
and other sounds.
Because surgery to save the lives of patients
with NF2 involves the removal of the hearing and balance nerves
along with the tumors of both ears (since NF2 produces bilateral
tumors), the nerve connections between the cochleas and the brain
are severed, resulting in profound deafness. The Auditory Brain
stem Implant (ABI) is similar in design and function to cochlear
implants and was developed to provide direct electrical stimulation
to that part of the brain stem that the hearing and balance nerves
once connected to.
Electrical stimulation of that part of the
brain stem results in somewhat less successful perception of
sound than cochlear implants. I don't personally know of any
ABI recipients who are able to understand speech without lipreading
or on a telephone, but the hope is that with the newer generation
of multi channel ABIs and the electrodes that are inserted directly
into the brain stem rather than being placed onto
the brain stem, speech recognition among ABI recipients might
be improved.
--- Mark Dessert
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