Neuroanatomical correlates of age-sensitive and age-invariant cognitive abilities: An in vivo MRI investigation

The relationship between brain asymmetry and age-related differences in cognitive abilities was examined in a sample of 29 healthy volunteers (18 to 78 years old). The volumes and areas of cerebral hemispheres as well as several cortical and subcortical regions were estimated from magnetic resonance imaging (MRI) scans. Fluid and crystallized intelligence were assessed by tests of nonverbal reasoning and vocabulary. The magnitude of leftward hemispheric volume asymmetry significantly and uniquely contributed to explaining the variance in both cognitive measures. None of the indices of regional hemispheric asymmetry showed a similar pattern of associations with intelligence. Although total brain size, and the size of dorsolateral prefrontal cortex positively correlated with fluid intelligence, they also correlated with age and head size, and did not add significantly to the fluid intelligence variance explained by age alone.