Electrical recordings from the surface of the brain or even from the outer surface of the head demonstrate that there is continuous electrical activity in the brain.Both the intensity and the patterns of this electrical activity are determined by the level of excitation of different parts of the brain resulting from sleep, wakefulness, or brain diseases such as epilepsy or even psychoses.The undulations in the recorded electrical potentials, shown in the picture , are called brain waves,and the entire record is called an EEG.
The intensities of brain waves recorded from the surface of the scalp range from 0 to 200 microvolts, and their frequencies range from once every few seconds to 50 or more per second.The character of the waves is dependent on the degree of activity in respective parts of the cerebral cortex and the waves change markedly between the status of wakefulness and sleep and coma.
Much of the time the brain waves are irregular,and no specific pattern can be discerned in the EEG.At other times distinct patterns do appear some of which are characteristic of specific abnormalities of the brain such as epilepsy which is discussed later.
The intensities of brain waves recorded from the surface of the scalp range from 0 to 200 microvolts, and their frequencies range from once every few seconds to 50 or more per second.The character of the waves is dependent on the degree of activity in respective parts of the cerebral cortex and the waves change markedly between the status of wakefulness and sleep and coma.
Much of the time the brain waves are irregular,and no specific pattern can be discerned in the EEG.At other times distinct patterns do appear some of which are characteristic of specific abnormalities of the brain such as epilepsy which is discussed later.