BRAIN MORPHOLOGY AND INTELLIGENCE

Although the correlations are modest (similar to r = 0.35), brain size as determined by magnetic resonance imaging has been positively relat ed to measures of psychometric intelligence. Three studies dealing wit h brain size-IQ relationships are presented in patients who have suffe red traumatic brain injury (TBI). Study 1 was an examination of whethe r the brain size-IQ relationship was proportionally maintained in resp onse to TBI-induced atrophic changes in the brain. Study 2 was an exam ination 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 a n examination of whether focal lesion volume plays a role in postinjur y brain size-IQ relations. Results indicated that trauma-induced atrop hic brain changes are related neither to postinjury IQ nor focal lesio n volume. However, patients with TBI with smaller brain size at the ti me of injury did have significantly lower postinjury IQ scores when co mpared 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 relations hips do not hold in the posttraumatic atrophic or focally damaged brai n indicates the complexity of the relation between brain size and morp hology.