accelerator is rotated around the target area in the patient's brain, allowing high doses of radiation to be given directly to the designated site. The procedure usually takes an entire day and is performed with a local anesthetic. A cat scan is used to determine the exact coordinates of the diseased tissue; with that information, doctors then affix a metal ring to the head, which helps the linear accelerator focus on the target area.
At present, this type of radiation is being used for patients with various types of brain tumors, as well as brain tumors that have not responded to conventional radiation therapy. It can also be used to treat malformed blood vessels in the brain that can cause seizures and are usually inoperable under normal situations.
The technique is also used to obtain a brain biopsy, to insert a permanent stimulating wire to control intractable pain, and to destroy areas of the brain to treat disabling neurological disorders.
Although the technique often costs less than traditional neurosurgery, it is still not widely practiced, and treatment is not always easy to find. For information on the technique, contact Elekta, 8 Executive Park West, Atlanta, GA 30329; (800) 535-73 55. For more information about brain tumor support groups, see Appendix I.
stimulants and the brain A class of drugs that increase nerve activity in the brain by triggering the release of norepinephrine. These drugs include
NICOTINE, CAFFEINE, AMPHETAMINES, and COCAINE.
There are two main types of stimulant drugs— those that stimulate the nerves of the central nervous system (including the amphetamines) and those that affect the respiratory system. central nervous system stimulants reduce drowsiness and increase alertness by their action on the reticular activating system in the brain stem. Respiratory stimulants act on the respiratory center in the brain stem. Nerve stimulants include caffeine, dextroamphetamine, and methylphenidate; respiratory stimulants include doxapram and nikethamide.
Caffeine boosts the brain's flow of thoughts and output of motor signals to the muscles. Too much caffeine can cause heartbeat and respiration to increase and bring on insomnia. Amphetamine is a synthetic product resembling ephedrine available as tablets, powder, or ampules for injection. They are chemically similar to the natural neurotrans-mitter noradrenalin, and enhance the activity of noradrenalin in the brain by releasing quantities of noradrenalin stored in nerve cells and preventing its reabsorption by blocking MAO. Amphetamine also may act on the receptors of certain cells.
Nerve stimulants can be given to treat narcolepsy (a disorder characterized by excess sleepiness); they are also effective in the treatment of hyperactivity in children. They may also suppress appetite, but their adverse effects make these drugs a poor choice in the treatment of obesity.
stimulus Any sensory event (such as a flashing light or the touch of a feather) that causes the brain to become active.
stimulus -response memory The kind of memory involved when a dinner gong triggers a trained dog to salivate. This type of memory takes place in the brain below the outer cortex and survives damage to regions of the brain that is essential for other types of memory.
Stokes-Adams syndrome Insufficient flow of blood to the brain caused by heart problems that result in recurrent, temporary loss of consciousness. In most cases, the heart begins beating regularly again, the skin reddens and the person wakes up.
Symptoms sudden attacks of fainting followed by a bluish tinge to the skin if the person does not regain consciousness quickly. There is a rapid breathing rate and slow pulse; seizures may occur due to lack of oxygen to the brain.
None needed if the patient wakes up. If consciousness does not return, prompt cardiopulmonary resuscitation may be needed to prevent brain damage. Most patients with this problem wear a pacemaker to regulate their heart rhythm and prevent future attacks.
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