Quantitative analysis of EEG signals: Time-frequency methods and ...

I will summarize here some of the experimental evidence supporting this view (for
more details see Basar, 1980, 1998, 1999 Basar et al., 1999):
1. In three year old children, neither spontaneous, nor evoked 10Hz activity is obtained
(Kolev et al, 1994, Basar-Eroglu et al., 1994). Then, according to the
resonance theory, in this case alpha rhythm does not belong to the natural brain
frequencies. In other words, alpha oscillations can not be evoked because there is
no spontaneous alpha activity.
2. High amplitude pre-stimulus 10Hz activity reduces the evoked potential amplitudes
(Basar, 1980 Basar and Stampfer, 1985 Basar et al., 1992), thus showing
an inverse relation between the pre-stimulus EEG and the evoked responses. An
inuence of pre-stimulus theta EEG was also reported on visual evoked potentials
(Basar et al., 1998). Then, since the background EEG inuences the evoked
responses, it can not be merely considered as additive noise.
3. Converging results support the view that evoked or induced oscillations can be
correlated, at least partially, with dierent functions, as it will be described in
sec. x2.3.3, thus showing that the frequency analysis of the evoked responses is not
arbitrary.
In conclusion, following the resonance theory, the ERP can be seen as evoked synchronization,
frequency stabilization, frequency selective enhancement and/or phase reordering
of the ongoing EEG, and it should not be interpreted as an additive component
to a noisy background EEG.
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