Important relation between EEG and brain evoked potentials

In this study, we analyze the important relation between the spontaneous and evoked activities of the substructures of the cat brain, such as the reticular formation, hippocampus, inferior colliculus, medial geniculate nucleus and acoustical cortex, with an ensemble of systems theory methods consisting of the following steps: (1) single auditory and/or visual evoked potentials (EPs) and the spontaneous activities (EEG) just preceding the stimuli are recorded from the brain center under study; (2) selectively averaged evoked potentials (SAEPs) are obtained from the recorded EPs; (3) amplitude frequency characteristics are computed from the AAEPs by means of Fourier transform; (4) the single EEG-EP sweeps are theoretically pass-band filtered with adequate band limits determined according to the selectivities revealed by the amplitude characteristics; (5) the EEG and EP components obtained in this way are compared with regard to the amplification in the population response upon the application of the stimulus. The results of this analysis support quantitatively our prediction of various types of resonance phenomena in a number of nuclei in the cat brain and in a large scale of frequencies from 1 Hz to 1000 Hz and show that the amplification factor related to resonance phenomena has probabilistic nature. Therefore, the analogy which we have recently drawn between the behaviors of a neural population and a random-phase probabilistic harmonic oscillator is extended by assigning also the amplitude and the frequency of the oscillations as random variables. A working hypothesis for the dynamics of neuronal populations is elaborated accordingly.Presented in Part at the Third European Meeting on Cybernetics and Systems Research 1976 in Vienna, April 20–23, 1976Supported by Grant No. TAG-345 of the Scientific and Technical Research Council of Turkey