of the waves change with the activity level of the brain. The tracings reveal that the electrical activity of the brain varies with the degree of alertness, depending on whether the subject is excited, relaxed, or in a deep sleep. The EEG brain-wave patterns include alpha waves (the primary pattern of an alert adult with closed eyes); the beta waves (lower, faster activity while a person is concentrating on an outside stimulus); delta waves (sleep patterns also found in infants; rarely, they are also caused by brain tumors); and theta waves (dominant pattern in children ages two to five and in psychopaths; also produced by frustration). In normal people, there are four types of brain waves: alpha, beta, theta and delta waves.

The technique was first tried medically in 1928, although scientists have known since the 1800s that it was possible to record electrical impulses from animal brains. Supplanted today by imaging studies in detecting brain pathology, the EEG is now used primarily to detect abnormal cerebral function that cannot be otherwise identified. It is therefore best used to evaluate transient states, such as seizures; evolving conditions, such as herpes simplex encephalitis; global disorders, such as dementia. Only a few EEG patterns can be used to diagnose a particular disease, but the tracings can be helpful in deciding among several disease alternatives.

in the technique, several small electrodes are attached to the scalp, connected to a device that measures and amplifies the brain's electrical impulses. Brain waves are measured while the patient opens and shuts the eyes, during and after hyperventilation and while looking at a flashing light. Sometimes, measurements are also taken as a patient drifts off to sleep.

electromyography A type of test that involves the continuous recording of the electrical activity of a muscle by inserting electrodes into the muscle fibers. The tracing is displayed on an oscilloscope or chart recorder. It is used to analyze peripheral nerve and muscular disorders and assess progress in recovery from some forms of paralysis.

Some discomfort is to be expected during this test, and patients can be premedicated with codeine or other drugs without altering the test results. The tests can be used to help diagnose


embolism, cerebral A blockage of one of the arteries that supplied blood to the brain. A cerebral embolism is one of the most common causes of stroke. The arteries are blocked by an embolus (blood clot, bubble of air or gas, bacteria, bone marrow, fat, and so on).

Survival depends on the speed with which blood flow is reestablished; if the embolus can be removed, long-term outlook for the patient is good.

Symptoms if the embolus causes a stroke, the symptoms depend on which part of the brain has been affected; it may cause an inability to speak, inability to walk, loss of consciousness, or visual problems.


Surgery (such as balloon angioplasty) to open the blocked arteries may be tried; if surgery is not possible, drugs designed to break up blood clots, and anticoagulant drugs (to prevent the formation of clots) may be given.

emotions and the brain Far from being a state of consciousness divorced from the physical brain, a person's emotions are produced by chemicals exquisitely intertwined with the physiological processes of the body so that in the truest sense what affects the body affects the mind and emotions, and vice versa.

The center of emotions in the brain can be found in the limbic system where the vast panoply of emotions is regulated through the release of excitatory and inhibitory neurotransmitters: Pleasure may be linked with chemical signals produced by the release of noradrenalin, and pain is associated with many neurotransmitters. Mood appears to be linked with serotonin and dopamine.

in response to a variety of stimuli, emotions arise in the limbic system, traveling along neural

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