Associations Between IQ, Total and Regional Brain Volumes, and Demography in a Large Normative Sample of Healthy Children and Adolescents

Abstract

In the course of efforts to establish quantitative norms for healthy brain development by magnetic resonance imaging (MRI) (Brain Development Cooperative Group, 2006), previously unreported associations of parental education and temporal and frontal lobe volumes with full scale IQ and its verbal and performance subscales were discovered. Our findings were derived from the largest, most representative MRI sample to date of healthy children and adolescents, ages 4 years 10 months to 18 years 4 months. We first find that parental education has a strong association with IQ in children that is not mediated by total or regional brain volumes. Second, we find that our observed correlations between temporal gray matter, temporal white matter and frontal white matter volumes with full scale IQ, between 0.14 to 0.27 in children and adolescents, are due in large part to their correlations with performance IQ and not verbal IQ. The volumes of other lobar gray and white matter, subcortical gray matter (thalamus, caudate nucleus, putamen, and globus pallidus), cerebellum, and brainstem do not contribute significantly to IQ variation. Third, we find that head circumference is an insufficient index of cerebral volume in typically developing older children and adolescents. The relations between total and regional brain volumes and IQ can best be discerned when additional variables known to be associated with IQ, especially parental education and other demographic measures, are considered concurrently.

Notes

*See Brain Development Cooperative Group Authorship List at the end of the article.

This work was supported by NINDS R01 NS34783 and NIMH P50 MH60450 (NL), RO1 HD048946 (EB) and NIMH RO1 MH080826 (JEL). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Mental Health or National Institutes of Health.

*Mean (SEM).

^†Derived from tables provided by the US Department of Housing and Urban Development and the US Census 2000.

^‡ N = 285, total sample size; n = 155 females, n = 130 males.

**Highest level attained by either parent.

^††Includes one participant neither of whose parents completed high school.

*N = 297 for VIQ and PIQ. Only those correlations for which p < .05 are shown.