The principle of EEG?

Generation and recording of EEG:

EEG is generally obtained by electrodes on the surface of the scalp. The mechanism of scalp potential generation is generally believed to be: when it is quiet, the apical dendrites of the pyramidal cells – the entire cell in the axis of the cell body are in a polarized state; when an impulse is transmitted to one end of the cell, it causes the end to be depolarized. The potential difference across the cell creates a bipolar electric field system, with current flowing from one end to the other. Since both the cytoplasm and the extracellular fluid contain electrolytes, current also passes outside the cell. This electrical activity can be recorded using scalp electrodes. In fact, the potential changes in the EEG on the scalp are a combination of many such bipolar electric fields. An EEG does not reflect the electrical activity of a nerve cell, but instead records the sum of the electrical activity of many groups of nerve cells in a region of the brain represented by the electrodes.
The basic components of EEG: The waveform of EEG is very irregular, and its frequency changes in the range of about 1 to 30 times per second. Usually this frequency change is divided into 4 bands: the frequency of delta wave is 0.5 to 3 times. /sec, the amplitude is 20-200 microvolts, normal adults can only record this wave when they are in deep sleep; the frequency of theta wave is 4-7 times per second, and the amplitude is about 100-150 microvolts, adults often sleep This wave can be recorded; theta and delta waves are collectively referred to as slow waves, and delta waves and theta waves are generally not recorded in awake normal people; the frequency of alpha waves is 8 to 13 times per second, and the amplitude is 20 to 100 microvolts. It is the basic rhythm of normal adult brain waves, which occurs when the eyes are awake and closed; the frequency of beta waves is 14 to 30 times per second, and the amplitude is 5 to 20 microvolts. The scope of thinking is wider, and the appearance of beta waves generally indicates that the cerebral cortex is in an excited state. The EEG of normal children is different from that of adults. Neonates are dominated by low-amplitude slow waves, and the frequency of brain waves gradually increases with age.
①α wave: frequency 8～13Hz, amplitude 10～100μV. All regions of the brain have, but the most obvious in the occipital region. Alpha rhythm is the main normal EEG activity in adults and older children when their eyes are awake and closed, and the alpha wave rhythm in children is gradually obvious with age.
②β wave: the frequency is 14～30Hz, and the amplitude is about 5～30/μV, which is more obvious in the frontal, temporal and central regions. Increases in mental activity and emotional excitement. About 6% of normal people still have beta rhythm in the recorded EEG even when they are mentally stable and eyes closed, which is called beta EEG.
③Theta wave: frequency 4～7Hz, amplitude 20～40μV.
④δ wave: frequency 0.5～3Hz, amplitude 10～20μV. Often appears on the forehead.