Date: Tue, 17 Sep 1996 13:03:49 -0400
From: Jacob Drollinger <[log in to unmask]>
There has been something on my mind for a while now, and I would like to
share a question with you.
Why would a typical P.D.er benefit from
having the signals to the pallidus blocked, such as in a pallidotomy and/or a
pallidal stimulation, when that brain structure is what controls the
reception of dopamine, and injury to such would leave one in my condition.
I know that only a small and very specific part of the pallidus is actually
frozen or de-activated by the two afore-mentioned procedures. However, the
fact that P.D. can be caused by an over-active reception of dopamine
confounds me. Maybe it has to do with there being less dopamine to receive,
and the receptors are going haywire trying to receive dopamine that isn't
there?
____________________________________
To understand how a pallidotomy works think of the brain as containing a
series of interconnected electrical circuits. In the parkinsonian one of these
circuits is overly active because there is not enough of the
neurotransmitter dopamine to regulate the electrical activity. A lesion
(small hole) is created on
the electrical pathway between the globus pallidus and the subthalamic
nucleus. Thus, using this metaphor, the overly active circuit is cut.
Through a procedure technically known as a Postero-Ventral Pallidotomy, a
probe will be inserted into a very precise location of the globus pallidus
approximately four inches beneath the top of the head. The patient remains
conscious under a local anesthetic. When the probe is in the correct position,
immediately adjacent to the optic nerve a small electrical charge will be
transmitted to the tip of the probe.
If the probe is too deep the patient will experience his/her very own
fireworks display and the probe will be slightly withdrawn. When it is properly
located there will be a slight twitch in the cheek or tongue. At that moment
heat will be generated to the probe tip and a small lesion will be created.
A simplistic explanation is this procedure creates lesions of
pallidofugal fibers leaving the globus pallidus on the way to the
thalamus. Rough Translation - An overly active neuronal pathway which
results in abnormal and extra-kinetic movements, is severed. Although the
Pallidotomy is not a cure it can eliminate many of the manifestations. The
results are instantaneous and appear to be long lasting.
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