130 Am J Psychiatry 1 50:1 , January 1993 Intelligence and Brain Structure in Normal Individuals Nancy C. Andreasen, M.D., Ph.D., Michael Flaum, M.D., Victor Swayze II, M.D., Daniel S. O’Leary, Ph.D., Randall Alliger, Ph.D., Gregg Cohen, M.S., James Ehrhardt, Ph.D., and William T.C. Yuh, M.D., M.S.E.E. Objective: This study was designed to evaluate the relation between intelligence and a variety ofmeasures ofbrain structure. Method: Magnetic resonance imaging scans were used to meas- ure the volume of the intracranial cavity, cerebral hemispheres, lateral ventricles, temporal lobes, hippocampus, caudate, and cerebellum, as well as the overall volume of gray matter, white matter, and CSF, in 67 healthy, normal volunteers. Intelligence was measured with the Wechsler Adult Intelligence Scale-Revised. Results: Full-scale IQ was found to be signifi- cantly correlated with intracranial, cerebral, temporal lobe, hippocampal, and cerebellar vol- ume but not with caudate and lateral ventricle volume. There were also significant correlations offull-scale, verbal, and performance IQ with overall gray matter volume but not with white matter or CSF volume. Gender differences were noted in the pattern and number of correla- tions between the volume of the brain and its subregions and full-scale, verbal, and perform- ance IQ. Conclusions: The results suggest that the size ofsome cerebral structures may account f or a significant, but modest, proportion of the variance in human intelligence. (Am J Psychiatry 1993; 150:130-1 34) M odern neunoimaging techniques offer an unpar- alleled opportunity to examine the relation be- tween brain structure and brain function in normal mdi- viduals. Because it is noninvasive and without significant risk, magnetic resonance imaging (MR!) permits in vivo quantitative measurements of brain size and the size of subregions (e.g., the hippocampus) that are thought to subserve known cognitive functions (e.g., memory). Controversy has persisted for many years about whether there are significant relationships between size and func- tion in the human brain. Geschwind’s seminal work, which indicates that the planum temponale is larger on the left side of the brain, reflecting left hemispheric spe- cialization for language, suggested that valid structure- function relationships might exist (1 ). Subsequent reports have suggested callosal enlargement in left-handed pen- sons, reflecting a higher degree of intenhemisphenic trans- fen as well as possible gender differences in brain structure (2-4). While many studies have been done with post-mom- tem tissue, more recently investigators have also used MRI to conduct “in vivo autopsies” to study these relationships in healthy, normal individuals, permitting the examina- tion of structure-function relationships independent of the Received March 24, 1 992; revision received July 14, 1 992; accepted Aug. 5, 1992. From the Mental Health Clinical Research Center and the Department of Radiology, University oflowa Hospitals and Clin- ics, and the Department of Psychiatry, University of Iowa College of Medicine. Address reprint requests to Dr. Andreasen, Mental Health Clinical Research Center, University of Iowa Hospitals and Clinics, 200 Hawkins Dr., Iowa City, IA 52242. Copyright © I 993 American Psychiatric Association. possible epiphenomena produced by aging, illness, death, on the fixation process (5-8). The relation between intelligence and brain size has been a particularly intriguing question. Several early reports suggested possible relationships between cra- nial size and intelligence or educational achievement, but these reports have been questioned for a variety of reasons (9-13). MRI has also been used to examine relationships between cerebral size and educational achievement, with the suggestion that a relationship may occur (14, 15). A recent report indicated a high con- relation (n=0.51 ) between !Q and cerebral size (16). This particular report focused on college students, who were designated as having a low IQ ( 1 03 on less, Wech- sler full-scale scone) on a high IQ (130 or more, Wech- sler full-scale score), thereby enhancing the probability of finding positive correlations between brain size and !Q. !n this article we report the finding of a similar nela- tionship, also based on MRI, in a larger and more gen- enalizable study group. In addition, we measured the size of brain subregions such as the hippocampus and assessed the total volume of gray matter in the brain, which provides an indirect indicator of neunonal den- sity and dendnitic expansion. METHOD The study group consisted of 67 healthy, normal vol- unteens recruited through newspaper advertising. They were screened with a structured interview to assess their