Ontogenetic patterns of frequency-power spectra elicited by flickering light in children: a comparative study of evoked and background EEGs.

Frequency-power spectra of the EEG evoked by repeptitive photic stimulation and of the background EEG were studied during childhood in 43 awake subjects aged between 2 months and 14 years. EEG activity was recorded from the middle parieto-occipital region with the aid of a 1-channel analyzer Lysograf-Alvar, analysing 16 frequencies in the range from 2 to 28 c/sec. The responsiveness of the central nervous system to flickering light improved in the course of childhood in parallel with the significant decline of delta activity and with the prominent increase of alpha intensity in the resting EEG. The 4th month of life appeared to be a marked turning point in the development of evoked and background EEGs. From that age, the bioelectric power at the flash rate corresponding to photic "driving" began to increase together with the highest and optimal driving frequencies. The flash rate, at which evoked potentials changed into the "driven" rhythm, also shifted towards higher frequencies. Subsequently, the amount of energy in the resting EEG increased significantly within the theta, alpha and beta bands and, on the contrary, a prominent decline was observed in the delta range. Marked ontogenetic changes at this age closely coincided with the rapid development of exogenous fibres in the occipital cortex, including the thalamo-cortical conncetions, and fibres of the neuropil in cortical layer I, which might play an important role in the genesis of background and "driven" in the occipital region.

[Development of optical evoked activity in the human]. / Die Entwicklung der optischen Reizaktivität beim Menschen.

A comparison with experimental results obtained from animals shows that the development in man of what is called evoked potentials is considerably more complicated. The neonatal type of human response is very similar to the pattern in adult animals. However, for the further development it is not possible to find an analogy in animals. The entire character of the response is changed, the number of waves being increased. Only the changes in latency are comparable with experimental results. The rate of development is different, too. In man, although he belongs to those mammals giving birth to very immature offsprings, the first responses show long before the time of childbirth. For the animals studied to date this is the case postnatally only. The results obtained show that the development of stimulated activity, i. e., of evoked potentials and photic driving, continues through all childhood. The evaluation of the individual parameters, therefore, is a suitable method for evolutionary studies of the human nervous system. It is appropriate to speak of electrophysiological criteria of the state of maturation of the central nervous system. The development of all parameters is most rapid in the first months of life. It certainly is not necessary to stress that this particular fact does not only reflect the conditions in the optical system, but that it is an expression of great and rapid changes in the entire central nervous system.