Spatial structure of the human alpha rhythm: global correlation in adults and local correlation in children

Objective: The maturation of the neocortex during childhood and adolescence involves dramatic increases in white-matter volume. EEG recordings from children and adults were examined to determine whether there are associated changes in spatial properties of dynamic processes in the neocortex. Methods: Spontaneous eyes-closed and eyes-open EEG were recorded at 128 electrodes in 20 children aged 6–11 years and 23 adults aged 18–23 years. The surface Laplacian algorithm was applied to improve the spatial resolution of each electrode. Power and coherence were used to characterize the spatial structure of the alpha rhythm. A stochastic field model was used to eliminate coherences that are inflated due to volume conduction. Results: In adults, the alpha rhythm is characterized by very high coherence between distant electrodes. The children demonstrated reduced anterior power and coherence between anterior and posterior electrodes at the peak alpha frequency in comparison to the adults. The Laplacian alpha rhythm demonstrated much higher power in the children at both anterior and posterior electrodes, but was weakly correlated between electrodes. Conclusions: The maturation of neocortex in late childhood involves increased global correlation by long-range corticocortical connections. The local correlation that contributes power to each electrode, independent of other electrodes, is reduced as the global correlation increases.