Poverty, cultural disadvantage and brain development: a study of pre-school children in Mexico.

Forty-two children, who had been studied previously at the age of 18-30 months, were studied again at 4 years of age. Twenty-two belonged to low socioeconomic strata and were classified as high-risk children (HRC) the other 20 were classified as low-risk children (LRC), and belonged to middle and middle-high socioeconomic strata. Ten minutes of EEG using reference derivations (with linked earlobes) were recorded from each subject. Twenty EEG segments of 3.2 s each were selected by visual inspection for Fourier analysis. Absolute power (AP) was computed for the total EEG energy (1.5-19 Hz) as well as each reference derivation in 4 frequency bands: delta (1.5-3.5 Hz), theta (4-7.5 Hz), alpha (7.5-12.5 Hz) and beta (12.5-19 Hz). HRC had significantly more delta AP than LRC in frontal and central leads, and higher values of theta AP in frontal leads. Alpha AP was higher in LRC in occipital areas and in F8 and T4. This study suggests a maturational lag in HRC.