Time and Frequency Analysis of the Brain‘s Distributed

uring the past 15 years, our research D group has published several reports about a working hypothesis on the brain’s electroencephalogram (EEG) and evoked potentials (EPs). This hypothesis had sev-eral interrelated issues. In our view, the conventional averaged EP- which is widely used and very popular- was con-sidered only as a rough estimate of brain’s EEG-response, and it was claimed that the averaged EP does not take into account dynamical changes in the brain’s intrinsic activity. On the contrary, both single EPs and EP-like EEG segments probably re-sulting from hidden sensory or cognitive stimulation were considered as the brain’s quasi-invariant resonant modes contain-ing important brain frequency codes re-lated to central nervous system function [l-41. The hypothesis explained in the lit-erature can be summarized as follows: 1) The EEG consists of the activity of an ensemble of generators producing rhythmic activity in several frequency ranges. Usually, these oscillators are ac-tive in a random manner; however, by application of sensory stimulation, these generators are coupled and act together in a coherent way. This synchronization and enhancement of EEG activity gives rise to an “evoked ” or “induced rhythmicity” (“alpha response, ” “theta response, ” “40 Hz (gamma) response ” etc.). Evoked po-tentials representing ensembles of neural population responses were considered as a result of transition from a disordered to an ordered state (For details of this anal-ogy also in the view of synergetics see [ 1, 2,511. 2) These rhythmicities may also occur without defined physical stimulation, but may be triggered by hidden sources, for example as a result of cognitive loading (internally induced rhythmicities) [6]. 3) The superposition of induced or evoked oscillations in various EEG-fre