SIZE ISNT EVERYTHING - A STUDY OF BRAIN VOLUME, INTELLIGENCE AND AUDITORY-EVOKED POTENTIALS

Although brain volumes calculated from magnetic resonance (MR) imaging have been found to correlate with IQ. the relationship between MR-derived brain volume and other mental processes has not been examined. Fifty normal-ability adults had their brain volume calculated using MR scanning, along with tasks measuring IQ, memory, and information-processing speed, and an auditory evoked potential (AEP) task. All MR scans were corrected for artefacts arising from inhomogenous coil response. Of the three AEP components measured, only P3 latency and amplitude were associated with measures of mental ability. Out of the 50 adults tested, 40 had usable MR records. Corrected for height and weight, total brain volume was associated with Full-Scale IQ (r = 0.32, P < 0.025); when this correlation was corrected for restricted range, the correlation increased to 0.66. Although there was no systematic pattern of associations between brain volume and individual measures of memory or information-processing speed for the bivariate correlations, adjusted R2s from exploratory multiple regression suggested that while information-processing speed shared 7% of test variance with brain volume, memory might account for 22%, and the complete test battery might account for as much as 32%. Our study therefore suggests a partial dissociation between mechanisms underlying intelligence, in that brain volume is associated with mental ability and memory, but not especially with information-processing speed.