The relationship between certain forms of potentials and the variations in brain excitability (based on EEG, recorded during photic stimuli triggered by rhythmic brain potentials)

Abstract

1. 1. It is known that timing of stimuli with reference to the phase of the brain waves affects the pattern of activity. Investigation into the exact nature of these relationships, however, raises considerable difficulties. Pertinent experimental data recorded in the literature reveal the contradictory results obtained by different investigators. 2. 2. The problem has been studied by the authors by using stimuli triggered by brain potential rhythms, with varying stimulus to phase relations. 3. 3. It has been shown that, within one single complete alpha cycle, there may be one, two, or even three, time zones during which the application of a stimulus evokes a synchronization of the activity. There may also be one, two, or three, time zones during which stimuli evoke enhanced desynchronization of potentials. 4. 4. There may be various degrees of dependence of the EEG pattern on the relationship between the stimulus and the phase of the brain wave, and there may be different degrees of the stability of this relationship. These may change under the effects of drugs and with alteration of the patient's condition. The results of this investigation are analyzed in terms of the current views on the relations between brain waves and variations in brain excitability, due consideration being given to Wedenski's concepts of the lability of neurodynamic structure.