EEG rhythmicities evoked by visual stimuli in three-year-old children.

The present paper complements our investigations on children's and adult's EEGs and evoked potentials elicited by mean of auditory stimulation. We analyzed the spectral characteristics of spontaneously recorded EEGs, visual evoked potentials, and frequency responses of a group of 3-year-old children. The results were compared to the corresponding measurements in adults aged 20-22 years. Our findings show that: 1. the main frequency VEP components in 3 years old children are "delta" and "theta responses" with delayed time courses in comparison to adult's VEPs, 2. the existence of a given frequency component in the VEPs depends on the presence of the corresponding rhythm in the spontaneous EEG, and 3. the individual filtered children's VEPs show larger variability in comparison to adults, as well as different interhemispheric variability in the different frequency ranges. It was concluded that the evoked frequency components depend on the frequency content of the spontaneous EEG rhythms and their development. However, some of the children already showed alpha enhancement as well as synchronized alpha waves in the poststimulus period at the occipital and parietal leads. The possible explanation of these phenomena might be referred to early development of the posterior basic rhythms as well as to known resonance phenomena such as weak resonance and tuning.