Lateralized theta wave connectivity and language performance in 2- to 5-year-old children

Abstract

Recent neuroimaging studies support the view that a left-lateralized brain network is crucial for language development in children. However, no previous studies have demonstrated a clear link between lateralized brain functional network and language performance in preschool children. Magnetoencephalography (MEG) is a noninvasive brain imaging technique and is a practical neuroimaging method for use in young children. MEG produces a reference-free signal, and is therefore an ideal tool to compute coherence between two distant cortical rhythms. In the present study, using a custom child-sized MEG system, we investigated brain networks while 78 right-handed preschool human children (32-64 months; 96% were 3-4 years old) listened to stories with moving images. The results indicated that left dominance of parietotemporal coherence in theta band activity (6-8 Hz) was specifically correlated with higher performance of language-related tasks, whereas this laterality was not correlated with nonverbal cognitive performance, chronological age, or head circumference. Power analyses did not reveal any specific frequencies that contributed to higher language performance. Our results suggest that it is not the left dominance in theta oscillation per se, but the left-dominant phase-locked connectivity via theta oscillation that contributes to the development of language ability in young children.

Figure 1.

A, In the custom child-sized MEG system, the MEG sensors are as close to the whole head as possible for optimal recording in young children. During MEG recording, the children lay supine on the bed and viewed video programs projected onto a screen. B, Distances between MEG sensors (temporal area) and hippocampus. In 3- to 4-year-old children (left), sensors were close enough to the parahippocampal gyrus to record its activity, whereas in a conventional MEG system (right), the distance is too great to obtain a good signal from the parahippocampal gyrus. Open circles indicate MEG SQUID sensors (rear view). C, Schema of five selected sensors and 10 connections of interest (solid line) in each hemisphere.

Figure 2.

A, Correlation coefficients between laterality index of intrahemispheric coherences and language-related cognitive performance. Note that a significant correlation was found in parietotemporal connectivity in theta-2 (r = 0.390, p < 0.0006). B, C, Correlation coefficients between intrahemispheric coherences and language-related cognitive performance in the left (B) or right (C) hemisphere. There were no significant correlations between intrahemispheric coherences and cognitive performance in either hemispheres (p ≥ 0.0006). *p < 0.0006.

Figure 3.

A, B, Scatter plot of laterality index of theta-2 band coherence (parietotemporal connectivity) and language-related cognitive performance (r = 0.390, p < 0.0006; A), and chronological age (r = 0.175, n.s.; B). ○, Boys (n = 36); •, girls (n = 42). Solid line, Regression line for boys; broken line; regression line for girls. L, left; R, right; n.s., not significant.