Brain morphology and intelligence

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Abstract
Although the correlations are modest (∼ r = 0.35), brain size as determined by magnetic resonance imaging has been positively related to measures of psychometric intelligence. Three studies dealing with brain size‐IQ relationships are presented in patients who have suffered traumatic brain injury (TBI). Study 1 was an examination of whether the brain size‐IQ relationship was proportionally maintained in response to TBI‐induced atrophie changes in the brain. Study 2 was an examination of whether smaller brain size at the time of injury was a risk factor for more significant decline in IQ after injury. Study 3 was an examination of whether focal lesion volume plays a role in postinjury brain size‐IQ relations. Results indicated that trauma‐induced atrophic brain changes are related neither to postinjury IQ nor focal lesion volume. However, patients with TBI with smaller brain size at the time of injury did have significantly lower postinjury IQ scores when compared to a matched group that had larger premorbid brain size. These latter findings are discussed in terms of potentially greater neuronal redundancy in the larger brain. The fact that brain size‐IQ relationships do not hold in the posttraumatic atrophie or focally damaged brain indicates the complexity of the relation between brain size and morphology.