Introduce of EEGElectroencephalography (EEG) is the recording of electrical activity along the scalp.EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain.Diagnostic applications generally focus on the spectral content of EEG, that is, the type of neural oscillations that can be observed in EEG signals.Human thinking and behavior are controlled by the cerebral cortex function which depends on the activities of the many cranial nerve cells whose activities can be observed in brain-waves.Considering this, brain-wave monitoring is a useful tool for objectively and continuously evaluating cerebral cortex function.EEG captures electrical changes that appear during the signal transition process among cranial nerve cells.So EEG has the advantages of non-invasiveness and relative ease of use for monitoring brain functions.EEG is the useful method to detect dementia because EEG measurement is cheap and easy to data collection more than others.According to a recent study, assessment of the cognitive function of brain activity using EEG is recognized as a useful for examining the changes in the brain during perceptive or cognitive activity and is known to be capable of objective evaluation of brain function Quantitative EEG analysis.Recently, a mapping function has been added to EEG equipment, and the mathematical analysis of EEG as well as its visual interpretation has become possible.Through the development of quantitative EEG analysis methods, it has become possible to ascertain the differences between signals which could not be previously detected, and it has also become possible to express them as quantitative numeric values.Furthermore, quantitative EEG(qEEG) analysis has an advantage in that non-specialists can be easily record brain waves with a computer.The EEG measurements can be separated into the component wavelengths using Fourier transformations.And qEEG analysis involves summation of the component wavelength.qEEG can be expressed in numerical values because discrete wavelengths can be calculated from the component frequencies.