**6. Mounting 25 active EEG electrodes (as element of "10-10"system)**

Volumetric intracerebral processes are characterized by suppression of neuronal activity (especially in the early stages of development). On the EEG, this is reflected in the registration of slow-wave activity, which is poorly localized using the 10-20 system.

To address this issue, in 2017, the International Federation of Clinical Neurophysiology (IFCN) recommended a system of 25 active electrodes in a 10-10 electrode system as the research standard. This system includes 25 active electrodes, against 19 in the standard "10-20" system, which is achieved by introducing three pairs of additional electrodes F9–F10, T9–T10, P9–P10, which allow recording biopotentials from the basal parts of the brain.

#### **6.1 Procedure for converting a "10-20"system to a "10-10"system**

The procedure for converting the "10-20" system to the "10-10" system includes the introduction of six additional electrodes into the wiring diagram: F9 T9 P9 and F10 T10 P10, one row down (20% of the nasion-inion distance) from the F7 T3 T5 electrodes F8 T4 T6 (**Table 1**).


**Table 1**

*Electrode connections accordingly, the device uses sockets.*

#### **Figure 1.**

*An example of creating a system 10-10 using additional channels of the device (Program "Neuron-Spectrum" LLC "Neurosoft," Russia, author's observation).*

Instrument socket Electrode X1 F9 X2 F10 X3 T9 X4 T10 X5 P9 X6 P10 For registration, an appropriate new mounting of electrodes is created (**Figure 1**).

### **7. Features of the examination when using a multichannel EEG system**

A traditional study with 21 scalp electrodes in a 10-20 system is carried out using simple electrode attachment systems, most often in the form of "caps" of intertwined elastic tubes or cords, and "bridge" electrodes, in which improved skin-electrode contact is achieved using physical solution. This is the so-called classical or "wet" EEG interface. Direct installation of electrodes on the scalp is also possible using needle electrodes or adhesive electrodes attached to the scalp with a paste or collodion gel. This system is used in cases of long recordings and sleep studies. In recent years, the "dry interface" system has been actively introduced, which does not require the use of conductive solutions, pastes, or gels. Each electrode of such a system has a chlorinesilver comb installed directly on the scalp, and the contact error is solved either by a larger electrode surface or by installing a signal microamplifier.

The classical EEG scenario represents a successive change in the recording of background activity and functional tests "on tape" or in one file, which allows the researcher to "scroll the record" to compare the characteristics of the bioelectrical activity of the brain under different conditions and under different external influences. Since the number of electrodes is small, and the distance between them is from 4 to 7 cm, then in such a system there are no strict requirements for determining the spatial location of each electrode.

*Practical Recommendations for Conducting an EEG Study in a Neurophysiological Laboratory DOI: http://dx.doi.org/10.5772/intechopen.108879*

However, the use of a multichannel system with more than 64 electrodes requires a more careful approach to creating a scalp-electrode system. A small distance between the electrodes of 1–2 cm requires careful use of solutions and gels, since with an overabundance of the latter, a common contact will occur between two adjacent electrodes and, accordingly, they will be "turned off" from the common recording system.

When using a 64-channel system, systems of ring electrodes pumped with an electrically conductive gel are more often used, but when using 128- and 256-channel systems, it is difficult to implement such a solution, since a large number of adjacent electrodes create the problem of forming "conductive bridges" and shorting adjacent electrodes to each other.

The next problem of the multichannel interface is the spatial localization of the electrodes. As mentioned earlier, the use of the 10-20 system and the use of visualphenomenological analysis allow the researcher to do without this information or use the simplest methods of approximation by the area-electrode type. But the highdensity system operates with a much larger number of electrodes located above the same zone, and the researcher uses various methods of analysis that require adequate consideration of differences and input data.

To solve this problem, both methods of a spherical model are currently used with the representation of the head as a sphere of a given radius with a uniform arrangement of electrodes on its surface, as well as more accurate methods of geodetic photogrammetry, which determines the position of the electrode from a series of spatial images with the construction of an individual three-dimensional model, or the method an electronic pointer that allows you to determine the position of the electrode and its connection with the brain structure obtained using the transformation of CT or MRI images (**Figure 2**).
