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deep brain stimulation A surgical procedure to
treat tremors in disorders such as PARKINSON’S DIS-
EASEand benign essential tremor. In such condi-
tions, researchers believe the BRAIN structures
responsible for fine motor movement become
unable to block extraneous NERVEsignals, allowing
far more nerve signals to reach the muscles. The
overstimulation results in the tremors. Deep brain
stimulation generally becomes a viable treatment
option when noninvasive measures are no longer
successful in controlling tremors and the tremors
are severe enough to disrupt daily living. The neu-
rosurgeon implants a thin wire with electrodes at
the tip into the thalamus or subthalamic nucleus,
structures of the brainstem responsible for fine
motor movement. A battery-powered pulse gener-
ator then sends electrical signals to the electrodes.
The signals block the thalamus or subthalamic
nucleus from sending extraneous nerve signals to
the muscles, which slows or stops the tremors.
The first step of deep brain stimulation surgery
is the placement of a stereotactic halo, a circular
brace the neurosurgeon attaches to the person’s
skull with local anesthetic to numb the areas of
the skull where the halo attaches. The halo holds
the instruments in precise position during the
OPERATION. The second step of the surgery is
implanting the electrodes. After injecting a local
anesthetic to numb the SKINand periosteum cov-
ering the cranium (which are the only areas that
contain nerves sensitive to PAIN), the neurosur-
geon drills a tiny hole and inserts a very thin insu-
lated wire, feeding it slowly to the thalamus or
subthalamic nucleus, using MAGNETIC RESONANCE
IMAGING(MRI) to visualize and guide the path of
the wire.
The person remains conscious and relatively
aware during this part of the surgery, so he or she

can respond to the neurosurgeon’s directions and

report any unusual effects. The neurosurgeon typ-

ically has the person hold a small object to moni-

tor improvement of the tremors with the

electrode’s placement and activation. During the

third and final stage of the operation the neuro-

surgeon implants the pulse generator into a

pocket of tissue beneath the clavicle (collarbone)

under local or sometimes general ANESTHESIAand

runs the other end of the insulated wire under the

skin to connect at the pulse generator. The neuro-

surgeon uses a computer to program the pulse

generator to deliver the appropriate STRENGTHand

rate of electrical impulses.

The operation lasts about 90 minutes. The neu-

rosurgeon removes the stereotactic halo when the

operation is finished. Minor side effects, usually

temporary, may include tingling and balance dis-

turbances from the wire passing through the

brain. Complications are rare; when they do occur

they may include excessive bleeding and postop-

erative INFECTION. Most people return to full and

regular activities within two weeks. The batteries

in the pulse generator last about five years, after

which the neurosurgeon replaces the pulse gener-

ator and batteries together. Deep brain stimulation

typically provides long-term relief from tremors,

though in degenerative conditions such as Parkin-

son’s disease the benefit eventually diminishes as

the condition progresses.

See also QUALITY OF LIFE; SURGERY BENEFIT AND RISK

ASSESSMENT; TREMOR DISORDERS.

delirium A state of extreme confusion generally

resulting from reversible causes. Delirium appears

to result from multiple imbalances in the brain’s

neurotransmitters. The causes of these imbalances

are generally multiple or complex, such as the