STIMULATION OF EXCITABLE TISSUES - Design and Development of Medical Electronic Instrumentation - page 313

9. Control of Parkinsonian tremor . Electrical stimulation of neuron clusters deep inside
the brain [also known as deep brain stimulation (DBS)] is now used to inactivate the sub-
thalamic nucleus, which is overactive in Parkinson's disease. A multielectrode lead is
implanted into the ventrointermediate nucleus of the thalamus. The lead is connected to a
pulse generator that is surgically implanted under the skin in the upper chest. When the
patient passes a magnet over the pulse generator, the device delivers high-frequency pulse
trains to the subthalamic nucleus to block the tremor.
10. Gastric “pacing . ” Electrical stimulation of the stomach is currently being used to
reduce symptoms of nausea and vomiting for patients su ering from gastroparesis (a stom-

ach disorder in which food moves through the stomach more slowly than normal).
11. Restoration of lost sight . Electrical stimulation of the retina, the optical nerve, and
the visual cortex is now developed to the point at which implants for functionally restor-
ing sights to blind patients will soon be available commercially. Functional sight may be
given to patients blinded by retinitis pigmentosa by using integrated circuits embedded in
contact with the retina. The ICs contain an array of photovoltaic cells that directly power
an array of microstimulators and electrodes to convert the image into a directly mapped
electrical image, bypassing degenerated photoreceptors and directly stimulating the
remaining nerve cells in the retina. For patients with blindness caused farther down the
optical nerve, the possibility exists of stimulating the visual cortex directly using micro-
electrode arrays to generate coherent images from phosphenes (sensation of a spot of light)
elicited by the electrical stimulation.
12. Restoration of lost hearing . Cochlear implants stimulate spinal ganglion cells of the
auditory nerves, bypassing nonfunctional hair cells to restore limited hearing in some types
of deafness. The cochlear implant system really consists of an implanted stimulator con-
nected to an electrode array inserted in the cochlea and an external speech processor that
codes the speech into stimulation patterns that can be translated back into sounds by the
brain. The external speech processor also powers the implant via an inductive energy trans-
fer link. Cochlear implants are now common and provide substantial bene

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fi ts to many pro-

foundly deafened children and adults. Bene ts vary by person and range from increased

perception of environmental sounds to the ability to use a telephone.
13. Restoration of lost or impaired neuromuscular function . Functional electrical stim-
ulation (FES), also known as functional neuromuscular stimulation (FNS), is a rehabilita-
tion strategy that applies electrical currents to the nerves that control paralyzed muscles in
order to stimulate functional movements such as standing or stepping. FNS systems include
either skin-surface or implanted electrodes, a control unit which often also receives motion
information back from sensors, and a stimulus generator. A number of FNS units are now
either available commercially or under clinical investigation. Typical applications of FNS
include controlling foot drop, enabling lower-limb paraplegics to stand or sit, and restoring
hand function to the paralyzed upper limb.
14. Maintenance or increase in range of movement . Electrical muscle stimulation
(EMS) is used to strengthen muscle and facilitate voluntary motor function. Although
EMS devices are often advertised for muscle toning and weight reduction, they are author-
ized by the FDA only as prescription devices for maintaining or increasing range of
motion, relaxation of muscle spasm, prevention or retardation of disuse atrophy, muscle
reeducation, increasing local blood circulation, and postsurgical stimulation of calf mus-
cles to prevent the formation of blood clots.
15. Electroconvulsive therapy (ECT). This is a relatively painless procedure that is

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e ective in treating major depression. A short, controlled set of electrical pulses is

given for about a minute through scalp electrodes to produce generalized seizures.
Biological changes that result from the seizure are believed to result in a change in
brain chemistry which is believed to be the key to restoring normal function. Because
patients are under anesthesia and have taken muscle relaxants, they neither convulse
nor feel the current.

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