**1.1 Importance of EEG over fMRI and PET**

EEG works as a good tool to explore brain activity and can detect changes within milliseconds. Depending upon the type of neuron, an action potential takes 0.5–130 milliseconds approximately to propagate across a single neuron. Whereas, other methods likewise fMRI and PET has time resolution in terms of seconds and minutes and makes these methods less efficient.

Moreover, EEG directly measures the brain's electrical activity, whilst other methods such as SPECT, fMRI record changes in blood flow, or PET record changes in metabolic activity, which are indirect markers of electrical activity belonging to the brain. The electrical activity is a superposition of the huge number of electrical charges arising from multiple sources likewise brain cells i.e. neurons and artifacts. It is possible to place electrodes inside the human head via surgery for direct measurement from different centers in the human brain, but this is a painful and risky procedure for the subject [3, 4]. However, the desirable technique is to calculate electrical signals of interest invaded on the scalp as shown in the following **Figure 2**.

Signals obtained by an above-maintained process are weighted sums of neuron activity, whose weights depend on the signal path from a specific brain cell to the connected electrodes. Since the same electrical potential is being recorded from more than one electrode, signals being occurred from those electrodes are supposed to be highly correlated [4]. Henceforth, Scientists and Researchers collect these recordings by attachment of tens or hundreds of electrodes, which are positioned in pairs, at various locations on the surface of the subject's head. These electrical potentials (Charges) are tested simultaneously via individuals' channels or amplifiers. Recording for each channel represents the difference in electrical potential between two areas under each electrode's pair [5] as represented in **Figure 3**. In **Figure 3**, the differences between the two electrodes are measured through an operational amplifier for generating EEG signal recording. A machine that is used for this purpose is known as an electroencephalograph, and recordings collected through these amplifiers are known as electroencephalogram (EEG) signals.

*Effective EEG Artifact Removal from EEG Signal DOI: http://dx.doi.org/10.5772/intechopen.102698*

#### **Figure 2.**

*EEG electrodes placement on a subject, monitoring various sectors of the brain for activities.*

#### **Figure 3.**

*Differential amplifier for EEG recording/signal.*

#### **1.2 Electroencephalograph measuring system**

Currently, so many different types of electroencephalographs are available; over which 10–20 system is the internationally standardized method for describing the location of scalp electrodes and is based upon the relationship between an electrode's location and cerebral cortex underlying area and usually employs 21 electrodes. Its positions are determined by dividing the skull into the perimeters by connection of a few reference points lying on the human head.

In this, every perimeter has a letter, that helps in the identification of the lobe, and either a number or another letter for identification of the hemisphere location. Letters that are used are as follows:

1."F"-Frontal lobe

2."T"-Temporal lobe

3."C"-Central lobe


Furthermore, numbers (2, 4, 6, 8) refer to the right hemisphere, whereas odd numbers (1, 3, 5, 7) refer to the left hemisphere.

In the below-shown **Figure 4**, the "Z" refers to an electrode placed on the midline; the position of the electrode can be determined by the magnitude of the number, the smaller magnitude represents that electrode is much closer to the midline. The figure given below presents the actual electrode placement on the head and from these points, skull perimeters are measured in the transverse and the median planes [4].

**Figure 3**.4 presents the system "10" and "20" shows the fact that the actual distances between two adjacent electrodes are in percentage of either 10% or 20% of the three main measurements:


#### **Figure 4.**

*The international 10–20 system seen from (a) left and (b) top (c) standard location and nomenclature of the intermediate 10% electrodes.*
