Alpha response system in children: changes with age

Evoked and event-related brain potentials (Eps, ERPs) may be regarded as originating from the reorganization of the spontaneous EEG rhythms (Başar, 1980). Until now, no data is available about the development of the evoked frequency components in EPs and ERPs of children. The main objective of the present research was to study the alpha response system in 6-11-year-old children. We suggested that the ability to reorganize the alpha activity and produce repeatable alpha patterns after external stimulation might undergo developmental changes that could reflect certain changes in information processing with increasing age from childhood to adulthood. Fifty 6-11-year-old children divided into five age groups, and 10 young adults were studied in a passive and an odd-ball condition. Alpha responses in the auditory EPs and non-target ERPs at Fz, Cz and Pz were analyzed. The magnitude and phase-locking with stimulus of single alpha responses were evaluated in the first 300 ms of the post-stimulus epoch. An original method was applied to assess quantitatively the repeatability (phase-locking) of the evoked alpha oscillations. The magnitude and the phase-locking to stimulus were analyzed with respect to their dependence on the age and topography factors. Our main results show that the alpha responses in 6-11-year-old children are different from those in adults: (1) Adults had significantly lower amplitude and stronger phase-locking than children; (2) Adults had maximal alpha amplitudes and phase-locking over the vertex, whereas children displayed maximal responses over the parietal site; (3) The phase-locking of eldest (10-11-year-old) children was as strong as in adults. Whereas no difference existed between groups of children in alpha response amplitudes, a significant increase in phase-locking from 6 to 11 years was observed. Concerning the obtained results we suggest that (1) Alpha response system is functionally involved in 6-11-year-old children, though its development is not complete at the age of 11, the upper limit of our sample (2) With regard to their differential developmental time-courses, the magnitude and the phase-locking parameters might be suggested to relate to different functional aspects of the alpha response system. The applied original method makes it possible to analyze the phase-locking to stimulus (or phase-reordering) separately and independently from the amplitude (enhancement) of the frequency responses, thus providing for a deeper examination of the evoked frequency components.