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| Electroencephalography |
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| Brain cells can generate electrical activity as a result of literally millions of action potentials of individual neurons. These electrical potentials are called brain waves and indicate activity of the cerebral cortex. Brain waves pass through the skull easily and can be detected by sensors called electrodes. A record of such waves is called an Electro encephalogram (EEG). EEG is the graphic representation of the electrical activity of the brain cells which are picked up by the electrodes placed on the scalp. The instrument used to prepare an EEG is called Electroencephalograph. |
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| An EEG is obtained by placing electrodes (16 - 30 in number) on the head and amplifying the waves with an electroencephalograph. The patterns of electrical activities are traced out as wavy lines on a moving sheet of graph paper or displayed on a computer screen. |
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| A typical recording takes 30 - 60 minutes. Four kinds of waves are produced by normal individuals representing different states of nervous activity. |
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| a) Alpha waves |
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| They are found in the EEGs of nearly all normal individuals when awake with eyes closed and in the resting stage. These waves disappear entirely during sleep. |
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| b) Beta waves |
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| Generally appear when the nervous system is active, during periods of sensory input and mental activity. Also it appears during tension. |
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| c) Theta waves |
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| The normally occur in children and in adults experiencing emotional stress. |
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| d) Delta waves |
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| Delta waves occur during deep sleep. They are normal in an awake infant. When produced by an awake adult, they indicate brain damage. |
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| Clinical Use |
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| Distinct EEG patterns appears in certain abnormalities. EEG is used clinically in the diagnosis of Epilepsy, Infectious diseases of the brain, tumours, trauma and Haematomas. It also furnishes information regarding sleep and wakefulness. It is also used to identify 'Brain death' that is the complete absence of brain waves. |
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