EEG spectrum as information carrier

Spontaneous and provoked changes of vigilance and consciousness are determined by TCS (thalamocortical system) activity. This is relatively easy to monitor using EEG, which is a complex curve but open to analysis, e.g., by means of FFT (fast Fourier transformation). Twenty six persons (six normal controls, twelve epileptics, eight dements) had EEG recorded during rest, reaction to sound, and perception to simple tones or chords from Smetana's symphonic poem Vysehrad. The length of reaction time was found dependent on FFT changes: the longer the time, the higher are the delta and the lower the alpha activities in the EEG spectrum. However, with alpha increasing during relaxation, the reaction time grew longer regardless of whether delta had increased due to hyperventilation, sleep or subclinical epileptic discharges. During the perception of tones, FFT showed changes in the alpha and delta bands different from those during the perception of chords, and different again during relaxation, and that in both normal controls and epileptics. The demented persons revealed no discernible FFT differences in the perception of either tones or chords, the only differences were found in the resting sections of the spectrum. One and the same stimulus produced a stereotype FFT response, i.e., different stimuli elicited different FFT response in healthy and epileptic persons. The dements responded to identical stimuli differently, and had stereotype FFT response elicited by the same stimuli. The results suggest that FFT can represent the information content of the EEG curve and, indirectly, also that of micro-EEG as it reverberates between the thalamus and the cortex in the form of neuronal activity impulsations. This interneuronal impulsation coding is disordered in dements with atrophy of the cortex; it is marked, on the one hand, by increased variability in the perception of identical stimuli, and, on the other hand, by impaired differentiation, and, consequently, by increasingly stereotype responses to different stimuli.