Consciousnessand EEG Spectrum

Overview

26 persons (6 normal controls, 12 epileptics, 8 demented subjects) had EEG recorded during rest,reaction to sound, and perception of simple tones or chords from Smetana’s symphonic poemVyšehrad. The length of reaction time depended on FFT changes: the longer the time, the higherare the delta and the lower the alpha activities in the EEG spectrum.However, with alpha increasing during relaxation, the reaction time was longer regardless ofwhether 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 fromthose during the perception of chords, and different again during relaxation, in both normalcontrols and epileptics. The demented persons revealed no discernible FFT differences in theperception of either tones or chords, the only differences were found in the resting portions of thespectrum.One and the same stimulus produced a stereotype FFT response, i.e., different stimuli eliciteda different a FFT response in healthy and epileptic persons. The demented a responded to identi-cal stimuli differently, and had a stereotype FFT response elicited by the same stimuli.The results suggest that FFT can represent the informational content of the EEG curve and,indirectly, also that of micro-EEG as it reverberates between the thalamus and the cortex in theform of neuronal activity impulses. This interneuronal impulse coding is impaired in dementedsubjects with atrophy of the cortex; it is marked, on the one hand, by increased variability in theperception of identical stimuli, and, on the other hand, by impaired differentiation, and, consequ-ently, by increasingly stereotype responses to different stimuli.Spontaneous and provoked changes of vigilance and consciousness are determined by TCS (thala-mocortical system) activity. This is relatively easy to monitor using EEG, which is a complexcurve but open to analysis, e.g., by means of FFT (fast Fourier transformation).

Key words:
EEG, consiousness, perception, dementia.