*1.1.1 Electroencephalogram (EEG)*

Electroencephalogram, EEG for short, is the human brain's electrical activity. Nerve system of human, including the brain, consists of neurons, which are nerve cells. The electrical current transmitted signals by neurons to other neurons [6]. The changes in voltage resulting from the electrical current are then measured by electrodes. Patterns form waves used by EEG and are sinusoidal. Based on the frequency bandwidth can be classified into several bands. Each band of waves corresponds to different activities. Most common bands classification [6]: Delta (0.5–4) HZ, Theta (5–7) HZ, Alpha (8–15) HZ, Beta (16–31) HZ, Gamma(32-higher) HZ, the correspondence for each band, **Table 1** describes each band and its activity.

It is the measurement of electrical activity of the brain, sensor used to obtain these signals. Brain consists of millions of neurons, and these neurons express emotions and thoughts as signals [7].

**Figure 1.** *Biometric types.*


**Table 1.**

*EEG bands description.*

"EEG measures the currents that flow during synaptic excitations of the dendrites of many pyramidal neurons in the cerebral cortex. Differences of electrical potentials are caused by summed postsynaptic graded potentials from pyramidal cells that create electrical dipoles between soma (body of neuron) and apical dendrites (neural branches) [5]."

The potentials are measured between two or more points called electrodes or sensors, which are placed on the scalp at different locations. EEG resembles waves, which is why the term brain waves is used when referring EEG signals. Padfield et al. [8], these EEG signals are unique for every individual and less exposed because it is under the scalp, which is hard to obtain and cannot be copied or manipulated [2].

Universality, uniqueness, permanency, performance, collectability, acceptability, and robustness satisfy the requirements of EEG-based biometric authentication method [7].
