The link between callosal thickness and intelligence in healthy children and adolescents

My friend Jeremy sent me this paper from Arthur Toga's lab at UCLA on the link between callosal thickness and intelligence in healthy children and adolescents after he heard one of my many talks about how to interpret negative relationships between white matter and intelligence.

In this study the authors selected a wonderfully well matched sample of children and adolescents: in the 4 age groups (6-8, 9-11, 12-14 and 15-17) there were 25 girls, 25 boys, 4 left handed boys and 1 left handed girl.  That's pretty freakin' incredible and really allowed them to investigate which age group or gender was driving the results from the whole group of 200 participants.

For ever subject they investigated how the thickness of the corpus callosum (at multiple points around the midsagittal cross section) could predict intelligence (as measured by the WASI).  The only result which passed correction for multiple comparison was a negative correlation in the splenium.  This means that children and adolescents with a smaller splenium tend to score more highly on IQ tests.

Correlations between callosal thickness and intelligence (overall sample).

When they unpack this finding by looking at the individual age groups and the interaction with gender the story becomes much more unclear.  In one age group male and female participants have completely opposite correlations!  In addition the location of significant (uncorrected) correlations changes across age groups and genders.

Sex- and age-specific correlations between callosal thickness and intelligence.

What certainly can be concluded from this paper is that the relationships between brain structure and intelligence are not static: they change thought out development.  The authors make a lovely argument that negative relationships in children are not necessarily at odds with positive correlations in adults.  Another great aspect of their argument is that they provide me with some great references to support it :)

Obviously, I'm always happy to see the sentiment: "only additional longitudinal studies addressing callosal microstructure will resolve the true nature of developmental changes."  Here's hoping I can help!!

The link between callosal thickness and intelligence in healthy children and adolescents.

Luders E, Thompson PM, Narr KL, Zamanyan A, Chou YY, Gutman B, Dinov ID, Toga AW.

Neuroimage. 2010 Oct 13. [Epub ahead of print] 
PMID: 20932920