Stronger intellectual abilities are associated with greater cortical thickness (CT) and cortical volume (CV); in relation to measured intelligence, CT and CV are more relevant measures than cortical surface area or cortical gyrification

The Relationship Between General Intelligence and Cortical Structure in Healthy Individuals. Sahil Bajaj et al. Neuroscience, https://doi.org/10.1016/j.neuroscience.2018.07.008

Highlights
•    Stronger intellectual abilities are associated with greater cortical thickness (CT) and cortical volume (CV).
•    The neural basis of intellectual abilities extends beyond fronto-parietal brain regions.
•    In relation to measured intelligence, CT and CV are more relevant measures than cortical surface area or cortical gyrification.

Abstract: Considerable work in recent years has examined the relationship between cortical thickness (CT) and general intelligence (IQ) in healthy individuals. It is not known whether specific IQ variables (i.e., perceptual reasoning [PIQ], verbal comprehension IQ [VIQ], and full-scale IQ [FSIQ]) are associated with multiple cortical measures (i.e., CT, cortical volume (CV), cortical surface area (CSA) and cortical gyrification (CG)) within the same individuals. Here we examined the association between these neuroimaging metrics and IQ in 56 healthy adults. At a cluster-forming threshold (CFT) of p < 0.05, we observed significant positive relationships between CT and all three IQ variables in regions within the posterior frontal and superior parietal lobes. Regions within the temporal and posterior frontal lobes exhibited positive relationships between CV and two IQ variables (PIQ and FSIQ) and regions within the inferior parietal lobe exhibited positive relationships between CV and PIQ. Additionally, CV was positively associated with VIQ in the left insula and with FSIQ within the inferior frontal gyrus. At a more stringent CFT (p < 0.01), the CT–PIQ, CT–VIQ, CT–FSIQ, and CV–PIQ relationships remained significant within the posterior frontal lobe, as did the CV–PIQ relationship within the temporal and inferior parietal lobes. We did not observe statistically significant relationships between IQ and either CSA or CG. Our findings suggest that the neural basis of IQ extends beyond previously observed relationships with fronto-parietal regions. We also conclude that CT and CV may be more useful metrics than CSA or CG in the study of intellectual abilities.

Abbreviations
CFT cluster-forming threshold
CG cortical gyrification
CSA cortical surface area
CT cortical thickness
CV cortical volume
FSIQ full-scale IQ
IQ intelligence
PIQ perceptual reasoning
VIQ verbal comprehension IQ