Relationship between IQ and Brain Size Summary: Monozygotic twins share numerous physical, psychological, and pathological traits. Recent advances in in vivo brain image acquisition and analysis have made it possible to determine quantitatively whether: 1) twins share neuroanatomical traits; and 2) neuroanatomical measures correlate with brain size. Using magnetic resonance imaging and computer-based image analysis techniques, measurements of the volume of the forebrain, the surface area of the cerebral cortex and the mid-sagittal area of the corpus callosum were obtained in 10 pairs of monozygotic twins. Head circumference, body weight, and Full-Scale IQ were also measured. Analyses of variance were carried out using genotype, birth order, and sex, as between-subject factors. Pearson correlation coefficients were computed to assess the interrelationships between brain measures, head circumference, and IQ. Effects of genotype (but not of birth order) were found for total forebrain volume, total cortical surface area, and callosal area. Consistent with previous twin studies, highly significant effects of genotype but not birth order were also found for head circumference, body weight, and Full-Scale IQ. The significant effect of genotype on all measures was not attributable to sex differences across unrelated twin pairs. Significant correlations were observed between forebrain volume, cortical surface area, and callosal area as well as between each brain measure and head circumference. No correlation between IQ and any other measure was found. Monozygotic twins share similarities in forebrain volume, cortical surface area, and callosal area. Brain measures are highly correlated with one another and with head circumference, but none is correlated with IQ. Authorization: Contact Authors Reference: Tramo MJ, Loftus WC, Green RL, Stukel TA, Weaver JB, Gazzaniga MS. Brain Size, Head Size, and IQ in Monozygotic Twins. Neurology 1998; 50:1246-1252. Description: This datafile contains 20 observations (10 pairs of twins) on 9 variables. This data set can be used to demonstrate simple linear regression and correlation. Variable Names in order from left to right: CCMIDSA: Corpus Collasum Surface Area (cm2) FIQ: Full-Scale IQ HC: Head Circumference (cm) ORDER: Birth Order PAIR: Pair ID (Genotype) SEX: Sex (1=Male 2=Female) TOTSA: Total Surface Area (cm2) TOTVOL: Total Brain Volume (cm3) WEIGHT: Body Weight (kg) 6.08 96 54.7 1 1 2 1913.88 1005 57.607 5.73 89 54.2 2 1 2 1684.89 963 58.968 6.22 87 53 1 2 2 1902.36 1035 64.184 5.8 87 52.9 2 2 2 1860.24 1027 58.514 7.99 101 57.8 1 3 2 2264.25 1281 63.958 8.42 103 56.9 2 3 2 2216.4 1272 61.69 7.44 103 56.6 1 4 2 1866.99 1051 133.358 6.84 96 55.3 2 4 2 1850.64 1079 107.503 6.48 127 53.1 1 5 2 1743.04 1034 62.143 6.43 126 54.8 2 5 2 1709.3 1070 83.009 7.99 101 57.2 2 6 1 1689.6 1173 61.236 8.76 96 57.2 1 6 1 1806.31 1079 61.236 6.32 93 57.2 2 7 1 2136.37 1067 83.916 6.32 88 57.2 1 7 1 2018.92 1104 79.38 7.6 94 55.8 2 8 1 1966.81 1347 97.524 7.62 85 57.2 1 8 1 2154.67 1439 99.792 6.03 97 57.2 1 9 1 1767.56 1029 81.648 6.59 114 56.5 2 9 1 1827.92 1100 88.452 7.52 113 59.2 2 10 1 1773.83 1204 79.38 7.67 124 58.5 1 10 1 1971.63 1160 72.576 Therese Stukel Dartmouth Hitchcock Medical Center One Medical Center Dr. Lebanon, NH 03756 e-mail: stukel@dartmouth.edu