Figure 17.3. Cap with sixty-four electrodes for EEG recording.A crude EEG can be recorded using only two electrodes attached to
a person’s head. However, EEGs typically use a larger number of elec-
trodes to obtain more interesting and precise recordings. By using as
many as 64 or 128 electrodes, it is possible to obtain a rough localiza-
tion of some of the sources of neural activity in the brain (Fig. 17.3).
And although spatial resolution is limited, EEG is marvelous for time
resolution. It is possible to measure changes in electrical activity that
are taking place on a millisecond time scale.
Atypical EEG recording is a mixture of a number of different fre-
quencies of electrical oscillation (Fig. 17.4). Various frequency ranges
have been given Greek-letter designations: delta (<4 Hz), theta (4-7