Page 134 - Handbook of Biomechatronics

Biomechatronic Applications of Brain-Computer Interfaces 131

(Da Silva, 2010) and can be detected using electrodes placed on the scalp
(Fig. 1). However, since the brain contains many different neurons and is
separated from the electrodes by layers of tissue (dura, skull, and skin),
any scalp electrode essentially measures the summed activity of thousands
of individual neurons. Furthermore, the signal obtained from the electrode
does not necessarily only reflect the activity of the neurons directly beneath
the electrode, but may also contain components originating from other
regions of the brain ( Jackson and Bolger, 2014). Finally, the tissues between
the brain and electrode essentially act as a low-pass filter, attenuating high-
frequency components of brain activity. Thus, high-quality hardware and
signal-processing approaches are required to obtain useful data from EEG.
EEG can be recorded from many locations on the scalp, depending on
the brain region of interest. To standardize EEG electrode placement,
researchers have developed the International 10–20 system to describe dif-
ferent electrode locations. A standard 10–20 layout is shown in Fig. 2, and
labels electrode sites according to their region and distance from the central
line of the head. For example, F sites are located in the frontal region (close
to the forehead) while C sites are located in the central region. Cz (C-zero) is
located in the center of the scalp while C1 is located slightly to the left of Cz
and C3 is located farther to the left of Cz; conversely, C2 is located slightly to
the right of Cz and C4 is located farther to the right.

Fig. 2 Electroencephalogram electrode placement on the scalp according to the Inter-
national 10–20 system. (From Nicolas-Alonso, L.F., Gomez-Gil, J., 2012. Brain computer
interfaces, a review. Sensors 12, 1211–1279, reused under the Creative Commons Attribu-
tion License.)