On me demandait d'être plus précis dans mes références. Dont acte.
Ci-dessous un panel de travaux récents concernant le rapport taille-volume du cerveau et QI. Comme je suis honnête, je cite également les études ne trouvant pas de corrélation (partie B).
Tous ces travaux ne sont pas également intéressants (certaines d'entre elles concernent des conditions-limites, comme les enfants prématurés).
A signaler : pour des raisons pratiques, je me suis limité à la base PubMed et à quelques mots-clés. Bon nombre d'études pertinentes n'y figurent pas (revues 'Intelligence', 'Psychometrika', etc.).
***
A/ Recherches trouvant des corrélations entre taille du cerveau (ou de certaines parties du cerveau) et intelligence.
Pediatr Res. 2004 May;55(5):884-93. Epub 2004 Feb 05.
Caudate and hippocampal volumes, intelligence, and motor impairment in 7-year-old children who were born preterm.
Abernethy LJ, Cooke RW, Foulder-Hughes L.
Department of Medical Imaging, Royal Liverpool Children's Hospital, Eaton Road, Liverpool L12 2AP, United Kingdom.
mailto:laurence.abernethy@rlch-tr.nwest.nhs.uk
Children who survive very preterm birth without major disability have a high prevalence of learning difficulty, attention deficit, and minor motor impairment (MMI). To determine whether these difficulties are associated with structural brain abnormalities, we studied 105 preterm children (<32 wk) at 7 y with tests of IQ and MMI (Movement ABC) and detailed magnetic resonance brain scans. Scans were assessed qualitatively for visible cerebral lesions. Volume measurements of the caudate nuclei and hippocampal formations were made. Total brain volume (TBV) was estimated from the head circumference. Qualitative assessment of the scans showed evidence of cerebral lesions in 20 (19%), which were associated with lower IQ and more frequent MMI. IQ correlated with right and left caudate volume (Spearman's rho 0.304 and 0.349; p < 0.01). This association persisted (except for verbal IQ) when caudate volume was expressed as a percentage of estimated TBV to allow for overall brain size. No significant correlations with hippocampal volumes were observed. These differences persisted when only scans from children without visible lesions on scan were considered. MMI was significantly associated only with TBV and was more common in children with evidence of thinning of the posterior corpus callosum, although most children with MMI have a normal corpus callosum. Lower IQs in children who were born preterm are related to poorer development of the caudate relative to the rest of the brain, independent of other lesions. These findings suggest abnormal brain development after perinatal injury or postnatal nutritional deficits is responsible for cognitive deficits in preterm children.
Neuroimage. 2004 Nov;23(3):800-5.
Mapping IQ and gray matter density in healthy young people.
Frangou S, Chitins X, Williams SC.
Section of Neurobiology of Psychosis, P066, Division of Psychological Medicine, Institute of Psychiatry, London SE5 8AF, UK.
mailto:sphasof@iop.kcl.ac.uk
Magnetic resonance imaging (MRI) studies suggest that significant changes in gray matter density occur during adolescence because of brain maturation. It has also been reported that gray matter volume correlates with measures of intellectual ability. This study examined whether the relationship between general intellectual ability (IQ) and gray matter morphometry reflects differential involvement of particular cytoarchitectonic areas. We found positive correlations between IQ and gray matter density in the orbitofrontal cortex, cingulate gyrus, the cerebellum, and thalamus and negative correlations in the caudate nucleus. These findings suggest that general intellectual ability in healthy young people is related to specific brain regions known to be involved in the executive control of attention, working memory, and response selection.
Neuroimage. 2004 Sep;23(1):425-33.
Structural brain variation and general intelligence.
Haier RJ, Jung RE, Yeo RA, Head K, Alkire MT.
Department of Pediatrics, University of California, Irvine, CA 92697-5000, USA.
mailto:rjhaier@uci.edu
Total brain volume accounts for about 16% of the variance in general intelligence scores (IQ), but how volumes of specific regions-of-interest (ROIs) relate to IQ is not known. We used voxel-based morphometry (VBM) in two independent samples to identify substantial gray matter (GM) correlates of IQ. Based on statistical conjunction of both samples (N = 47; P < 0.05 corrected for multiple comparisons), more gray matter is associated with higher IQ in discrete Brodmann areas (BA) including frontal (BA 10, 46, 9), temporal (BA 21, 37, 22, 42), parietal (BA 43 and 3), and occipital (BA 19) lobes and near BA 39 for white matter (WM). These results underscore the distributed neural basis of intelligence and suggest a developmental course for volume--IQ relationships in adulthood.
Brain. 2004 Feb;127(Pt 2):321-9. Epub 2003 Nov 25.
Critical periods of brain growth and cognitive function in children.
Gale CR, O'Callaghan FJ, Godfrey KM, Law CM, Martyn CN.
MRC Environmental Epidemiology Unit (University of Southampton), Southampton General Hospital, Southampton SO16 6YD, UK.
There is evidence that IQ tends to be higher in those who were heavier at birth or who grew taller in childhood and adolescence. Although these findings imply that growth in both foetal and postnatal life influences cognitive performance, little is known about the relative importance of brain growth during different periods of development. We investigated the relationship between brain growth in different periods of pre- and postnatal life and cognitive function in 221 9-year-old children whose mothers had taken part in a study of nutrition in pregnancy and whose head circumference had been measured at 18 weeks gestation, birth and 9 months of age. Cognitive function of the children and their mothers was assessed with the Wechsler Abbreviated Scale of Intelligence. Full-scale IQ at age 9 years rose by 1.98 points [95% confidence interval (CI) 0.34 to 3.62] for each SD increase in head circumference at 9 months and by 2.87 points (95% CI 1.05 to 4.69) for each SD increase in head circumference at 9 years of age, after adjustment for sex, number of older siblings, maternal IQ, age, education, social class, duration of breastfeeding and history of low mood in the post-partum period. Postnatal head growth was significantly greater in children whose mothers were educated to degree level or of higher socio-economic status. There was no relation between IQ and measurements of head size at 18 weeks gestation or at birth. These results suggest that brain growth during infancy and early childhood is more important than growth during foetal life in determining cognitive function.
Acta Paediatr. 2003 Oct;92(10):1138-43.
Birth characteristics and different dimensions of intellectual performance in young males: a nationwide population-based study.
Lundgren EM, Cnattingius S, Jonsson B, Tuvemo T.
Department of Women's and Children's Health, Uppsala University, Uppsala University Hospital, Sweden.
mailto:Maria.Lundgren@kbh.uu.se
AIM: To study the effect of size at birth on different dimensions of intellectual capacity. METHODS: The study comprised a population-based cohort including all male single births without congenital malformations in Sweden from 1973 to 1976, and conscripted before 1994 (n = 168 068). Information from the Swedish Birth Register was individually linked to the Swedish Conscript Register. The test of intellectual performance included four different dimensions: logical, spatial, theoretical and verbal capacity. These data were available for 80-86% of the males at conscription. RESULTS: Compared with boys born appropriate for gestational age, males born small for gestational age (SGA) had an increased risk for subnormal performance in all four dimensions. Among males born SGA who were also of short adult stature at conscription, and in individuals born SGA with a head circumference <-- 2 SDS at birth, the risk of subnormal performance was most marked in the logical dimension (OR 1.52; CI 1.25-1.84 and 1.33; 1.15-1.55, respectively). CONCLUSIONS: Being born small for gestational age is associated with increased risk of subnormal capacity in all four dimensions of intellectual performance. In SGA males, short adult stature, or a small head circumference at birth is especially associated with the risk of subnormal logical performance.
Twin Res. 2003 Apr;6(2):131-9.
Genetic correlations between brain volumes and the WAIS-III dimensions of verbal comprehension, working memory, perceptual organization, and processing speed.
Posthuma D, Baare WF, Hulshoff Pol HE, Kahn RS, Boomsma DI, De Geus EJ.
Department of Biological Psychology, Vrije Universiteit, van der Boechorststraat 1, 1081 BT Amsterdam, the Netherlands.
mailto:danielle@psy.vu.nl
We recently showed that the correlation of gray and white matter volume with full scale IQ and the Working Memory dimension are completely mediated by common genetic factors (Posthuma et al., 2002). Here we examine whether the other WAIS III dimensions (Verbal Comprehension, Perceptual Organization, Processing Speed) are also related to gray and white matter volume, and whether any of the dimensions are related to cerebellar volume. Two overlapping samples provided 135 subjects from 60 extended twin families for whom both MRI scans and WAIS III data were available. All three brain volumes are related to Working Memory capacity (r = 0.27). This phenotypic correlation is completely due to a common underlying genetic factor. Processing Speed was genetically related to white matter volume (r(g) = 0.39). Perceptual Organization was both genetically (r(g) = 0.39) and environmentally (r(e) = -0.71) related to cerebellar volume. Verbal Comprehension was not related to any of the three brain volumes. It is concluded that brain volumes are genetically related to intelligence which suggests that genes that influence brain volume may also be important for intelligence. It is also noted however, that the direction of causation (i.e., do genes influence brain volume which in turn influences intelligence, or alternatively, do genes influence intelligence which in turn influences brain volume), or the presence or absence of pleiotropy has not been resolved yet.
Neurology. 2002 Jul 23;59(2):169-74.
Intracranial capacity and brain volumes are associated with cognition in healthy elderly men.
MacLullich AM, Ferguson KJ, Deary IJ, Seckl JR, Starr JM, Wardlaw JM.
Geriatric Medicine Unit, University of Edinburgh, Edinburgh, Scotland, UK.
mailto:a.maclullich@ed.ac.uk
BACKGROUND: Brain size and intracranial capacity are correlated with cognitive performance in young healthy adults, but data are lacking on these relationships in older healthy adults. OBJECTIVE: To test the hypotheses that intracranial capacity, volumes of specific brain regions, and a measure of the shared variance between brain regions are positively associated with cognitive function in a sample of healthy, unmedicated elderly men (n = 97; mean age 67.8, SD 1.3). METHODS: Individuals underwent MRI, with measurements of intracranial area and volumetric measurements of hippocampi, temporal lobes, and frontal lobes. Cognitive testing included measures of premorbid intelligence, fluid intelligence, verbal memory, visuospatial memory, verbal fluency, and attention and processing speed. RESULTS: Cognitive tests showed significant positive intercorrelations throughout, and regional brain volumes were also universally, significantly, and positively intercorrelated. Intracranial area and several regional brain volumes correlated with tests of premorbid and fluid intelligence and tests of visuospatial memory. Tests of verbal memory and verbal fluency did not correlate significantly with brain volumes. Structural equation modeling demonstrated that the relationships between specific cognitive tests and regional brain volumes could best be summarized by a significant positive relationship between a general brain size factor and a general cognitive factor, and not by associations between individual tests and particular brain regions. CONCLUSIONS: In healthy elderly men, there are significant relationships between multiple cognitive tests and both intracranial capacity and regional brain volumes. These relationships may be largely due to longstanding associations between general cognitive ability and overall brain size.
Percept Mot Skills. 2003 Feb;96(1):3-17.
Cognitive correlates of medial temporal lobe development across adolescence: a magnetic resonance imaging study.
Yurgelun-Todd DA, Killgore WD, Cintron CB.
Cognitive Neuroimaging Laboratory, Brain Imaging Center, McLean Hospital, Harvard Medical School, Belmont, MA 02478, USA.
mailto:ytodd@mclean.harvard.edu
Adolescent development involves progressive changes in brain structure and cognitive function, but relatively few studies have documented the cognitive correlates of differences in structural brain volumes in this age group. We examined the relations among age, cognitive processing, and mesial temporal lobe volume in 37 children and adolescents. Participants completed a brief cognitive assessment battery and underwent volumetric structural magnetic resonance imaging. For the sample as a whole, amygdala volume correlated positively with age, and larger volumes of both the left and right amygdala were significantly associated with better performance on several cognitive tasks assessing academic skills and acquired knowledge in long-term memory. In contrast, hippocampal volumes did not correlate with adolescents' age and were less frequently correlated with cognitive performance. Amygdala volumes were most predictive of cognitive abilities in boys, whereas for girls, the volume of the hippocampus contributed more frequently to the prediction of cognitive abilities. These data suggest that measurable differences in mesial temporal volumes during adolescence are reliably associated with long-term cognitive abilities, particularly academic skills and the acquisition of intellectual knowledge, and that these relationships may differ as a function of the sex of the child.
Int J Neurosci. 2003 Jul;113(7):893-902.
Relationships between nonverbal IQ and brain size in right and left-handed men and women.
Akgun A, Okuyan O, Baytan SH, Topbas M.
Black Sea Technical University, Medical School, Department of Physiology, Trabzon, Turkey.
This study was designed to evaluate the relationship between nonverbal IQ and brain size in men and women. A significant correlation was found between IQ and brain size in total subjects. There was no significant correlation between these variables in women; men exhibited only a weak relation of brain size to IQ. In both left-handed men and women significant correlations were found between IQ and brain size. The results supported the hypothesis about the relation of IQ to brain size, suggesting that the sex difference in the cranial capacity and cerebral asymmetry might contribute to the diversity in cognitive functions.
Neurology. 2001 Apr 10;56(7):969-71.
Head size and cognitive ability in nondemented older adults are related.
Tisserand DJ, Bosma H, Van Boxtel MP, Jolles J.
Brain & Behavior Institute, Maastricht University, the Netherlands.
mailto:d.tisserand@np.unimaas.nl
In a cross-sectional analysis of 818 healthy older individuals (aged 50 to 81 years), head size was found to be related to performance on tests measuring intelligence, global cognitive functioning, and speed of information processing, but not memory. These relations were not confounded by educational level, socioeconomic background, or height. Large head/brain size may protect elderly people against cognitive deterioration, supporting a reserve hypothesis of brain aging.
J Cogn Neurosci. 2000 Jan;12(1):223-32.
A twin MRI study of size variations in human brain.
Pennington BF, Filipek PA, Lefly D, Chhabildas N, Kennedy DN, Simon JH, Filley CM, Galaburda A, DeFries JC.
Department of Psychology, University of Denver, CO 80208, USA.
Although it is well known that there is considerable variation among individuals in the size of the human brain, the etiology of less extreme individual differences in brain size is largely unknown. We present here data from the first large twin sample (N=132 individuals) in which the size of brain structures has been measured. As part of an ongoing project examining the brain correlates of reading disability (RD), whole brain morphometric analyses of structural magnetic response image (MRI) scans were performed on a sample of adolescent twins. Specifically, there were 25 monozygotic (MZ) and 23 dizygotic (DZ) pairs in which at least one member of each pair had RD and 9 MZ and 9 DZ pairs in which neither member had RD. We first factor-analyzed volume data for 13 individual brain structures, comprising all of the neocortex and most of the subcortex. This analysis yielded two factors ("cortical" and "subcortical") that accounted for 64% of the variance. We next tested whether genetic and environmental influences on brain size variations varied for these two factors or by hemisphere. We computed intraclass correlations within MZ and DZ pairs in each sample for the cortical and subcortical factor scores, for left and right neocortex, and for the total cerebral volume. All five MZ correlations were substantial (r's=.78 to.98) and significant in both samples, as well as being larger than the corresponding DZ correlations, (r's=0.32 to 0.65) in both samples. The MZ-DZ difference was significant for 3 variables in the RD sample and for one variable in the smaller control sample. These results indicate significant genetic influences on these variables. The magnitude of genetic influence did not vary markedly either for the 2 factors or the 2 hemispheres. There was also a positive correlation between brain size and full-scale IQ, consistent with the results of earlier studies. The total cerebral volume was moderately correlated (r=.42, p<.01, two-tailed) with full-scale IQ in the RD sample; there was a similar trend in the smaller control sample (r=.31, p<.07, two-tailed). Corrections of similar magnitude were found between the subcortical factor and full-scale IQ, whereas the results for the cortical factor (r=.16 and.13) were smaller and not significant. In sum, these results provide evidence for the heritability of individual differences in brain size which do not vary markedly by hemisphere or for neocortex relative to subcortex. Since there are also correlations between brain size and full-scale IQ in this sample, it is possible that genetic influences on brain size partly contribute to individual differences in IQ.
Neuropsychiatry Neuropsychol Behav Neurol. 1997 Jan;10(1):1-8.
Cerebellar size and cognition: correlations with IQ, verbal memory and motor dexterity.
Paradiso S, Andreasen NC, O'Leary DS, Arndt S, Robinson RG.
Department of Psychiatry, University of Iowa College of Medicine, Iowa City, USA.
The objective of this study was to examine the structure/function relationship between in vivo cerebellar size and higher cognitive function in a sample of healthy young subjects. The design of the study involved correlation of in vivo cerebellar volume measurements with measures of general intelligence (WAIS-R V&P FSIQ, Vocabulary, Block Design, and Digit Span subtests), motor dexterity (Halstead-Reitan Finger Tapping), verbal (WMS Logical Memory), and visual (Rey-Osterrieth Figure) memory covaring for cerebrum size. A similar analysis was performed using left temporal lobe volumes as a control region. The sample consisted of 62 healthy subjects (30 females, 32 males) enrolled as controls at the MHCRC at the University of Iowa Hospitals and Clinics. This independent sample does not overlap with the groups studied in our previous report on the relationship between cerebellar and brain size and IQ. Cerebellar and total brain size were estimated through automatic, atlas-based volume measurements using MR images obtained with a T1-weighted three-dimensional SPGR sequence on a 1.5-T GE Signa scanner and locally developed software. Cerebellar volume significantly correlated with Finger Tapping (left hand: r = 0.218, p < 0.05; right hand: r = 0.211, p < 0.05) and with memory retention of complex narrative material (r = 0.27, p < 0.02). Cerebellar volume correlated with general intelligence in the expected direction (r = 0.19, p < 0.07). This study confirms previous work indicating that the cerebellum may make a contribution to several aspects of cognition. Cerebellar volume significantly correlated with the ability to retain already encoded information in the verbal domain and with fine motor dexterity. Cerebellar volume positively correlated with general but the relationship did not reach statistical significance. The structural/functional relationship between cerebellum and verbal memory abilities is consistent with evolutionary theory for the phylogenetical increase in the size of the cerebellum.
Brain. 1996 Oct;119 ( Pt 5):1763-74.
Brain development, gender and IQ in children. A volumetric imaging study.
Reiss AL, Abrams MT, Singer HS, Ross JL, Denckla MB.
Kennedy Krieger Institute, Baltimore, MD 21205, USA.
Normal brain development during childhood is a complex and dynamic process for which detailed scientific information is lacking. MRI techniques, combined with methods for advanced image analysis, offer the potential to begin to construct a quantitative map of normal paediatric brain development in vivo. In this study we utilize volumetric analysis of high resolution brain images obtained from MRI to describe cerebral development and morphology in 85 normal children and adolescents ranging in age from 5 to 17 years. The results show that total cerebral volume is 10% larger in boys compared with girls. However, both boys and girls show little change in total cerebral volume after the age of 5 years. Increased cortical grey matter is the primary contributor to larger brain volume in boys, thus supporting the hypothesis that gender associated differences in brain size are related to differences in cortical neuronal density. Prominent, age-related changes in grey matter, white matter and CSF volumes are evident during childhood and appear to reflect ongoing maturation and remodelling of the CNS. Both boys and girls show a similar pattern of cerebral asymmetry; a rightward prominence of cortical and subcortical grey matter and a leftward prominence of CSF is observed. IQ is positively correlated with total cerebral volume in children, in particular, with the volume of cortical grey matter in the prefrontal region of the brain. Subcortical grey matter also contributes to the variance in IQ, although to a lesser extent than cortical grey volume. Quantitative knowledge of the developing human brain will play an increasingly greater role in improving sensitivity and specificity in the interpretation of brain abnormalities in patients within the clinical environment, as well as in groups of children with suspected brain dysfunction in the research setting.
J Clin Exp Neuropsychol. 1994 Feb;16(1):79-83.
Callosal morphology and performance on intelligence tests.
Strauss E, Wada J, Hunter M.
Department of Psychology, University of Victoria, B.C., Canada.
Variation in the size of the human corpus callosum was examined in relation to variation in measured IQ. The midsagittal surface area of the corpus callosum, obtained by magnetic resonance imaging, was measured in 47 patients with epilepsy. Intellectual ability was positively related to a larger posterior callosal area. We suggest that the relationship between the posterior callosal region and measured intelligence is "non-functional" in itself, but rather, may reflect other anatomical-cognitive associations. That is, differences in splenial size may reflect differences in the number of cortical neurons and interconnections between areas of the brain that are important for processing the kind of information measured on intelligence tests. Our conclusions, however, must be tempered by a number of factors; in particular, the nature of our subjects and the relatively small sample size.
Can J Exp Psychol. 1993 Dec;47(4):748-50; 751-6.
Brain size and intelligence in man: a correction to Peters.
Lynn R.
University of Ulster, Coleraine, Northern Ireland.
Peters' claim that there is no association between brain size and IQ is incorrect. Numerous studies show that there is a statistically significant correlation between the two.
Am J Psychiatry. 1993 Jan;150(1):130-4.
Intelligence and brain structure in normal individuals.
Andreasen NC, Flaum M, Swayze V 2nd, O'Leary DS, Alliger R, Cohen G, Ehrhardt J, Yuh WT.
Mental Health Clinical Research Center, University of Iowa Hospitals and Clinics, Iowa City 52242.
OBJECTIVE: This study was designed to evaluate the relation between intelligence and a variety of measures of brain structure. METHOD: Magnetic resonance imaging scans were used to measure 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 significantly correlated with intracranial, cerebral, temporal lobe, hippocampal, and cerebellar volume but not with caudate and lateral ventricle volume. There were also significant correlations of full-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 correlations between the volume of the brain and its subregions and full-scale, verbal, and performance IQ. CONCLUSIONS: The results suggest that the size of some cerebral structures may account for a significant, but modest, proportion of the variance in human intelligence.
Psychol Rep. 1992 Dec;71(3 Pt 1):811-21.
Contributions to the history of psychology: XC. Evolutionary biology and heritable traits (with reference to oriental-white-black differences): the 1989 AAAS paper.
Rushton JP.
Department of Psychology, University of Western Ontario, London, Canada.
Genetic distance estimates calculated from DNA sequencing indicate that in years since emergence from the ancestral hominid line, Mongoloids = 41,000, Caucasoids = 110,000, and Negroids = 200,000. Data also show that this succession is matched by numerous other differences such that Mongoloids > Caucasoids > Negroids in brain size and intelligence (cranial capacity = 1448, 1408, 1334 cm3; brain weight = 1351, 1336, 1286 gm.; millions of excess neurons = 8900, 8650, 8550; IQ = 107, 100, 85); maturational delay (age to walk alone, age of first intercourse, age of death); sexual restraint (ovulation rate, intercourse frequencies, sexually transmitted diseases including AIDS); quiescent temperament (aggressiveness, anxiety, sociability); and social organization (law abidingness, marital stability, mental health). This pattern is ordered by a theory of r/K reproductive strategies in which Mongoloids are posited to be more K-selected than Caucasoids and especially more than Negroids. (K-selected reproductive strategies emphasize parental care and are to be contrasted with r-selected strategies which emphasize fecundity, the bioenergetic trade-off between which is postulated to underlie cross-species differences in brain size, speed of maturation, reproductive effort, and longevity.) It is suggested that this pattern came about because the ice ages exerted greater selection pressures on the later emerging populations to produce larger brains, longer lives, and more K-like behavior. One theoretical possibility is that evolution is progressive and that some populations are more "advanced" than others. Predictions are made concerning economic projections and the spread of AIDS.
Genet Soc Gen Psychol Monogr. 1991 Aug;117(3):313-57.
Biological factors and psychometric intelligence: a review.
Johnson FW.
School of Education, University of California, Berkeley.
Results from a synthesis of correlations between psychometric intelligence and two physical traits, head size and body size, are reported. Within-family studies are reviewed for evidence of pleiotropy, the effect of a single genetic factor on two traits. Studies are also reviewed to determine whether prenatal effects bias twin studies, leading to underestimates of genetic influence. An N-weighted mean partial correlation (controlling height) of .10 between intelligence and head size was found. Using a method developed by Van Valen (1974), the correlation of intelligence and brain size was estimated as .29 based on all the intelligence/head-size studies of adults and adolescents, and .44 based on studies measuring intelligence with IQ tests. The N-weighted mean partial correlations (controlling age) of intelligence and height were .18 for children and .22 for adults. The within-family studies indicated that pleiotropy may contribute to the correlation of intelligence with head size and to the correlation of intelligence with body size. Prenatal effects are not an important source of bias in twin studies or for heritability estimates based on them.
Am J Dis Child. 1976 May;130(5):481-7.
Children with superior intelligence at 7 years of age: a prospective study of the influence of perinatal, medical, and socioeconomic factors.
Fisch RO, Bilek MK, Horrobin JM, Chang PN.
Perinatal and medical information, growth, and the social background of 258 children who, in a prospective study, had superior intelligence at 7 years of age were reviewed. The subjects were divided into three categories on the basis of the results of psychological evaluation at age 7. Comparisons were made between those with superior (intelligence quotient greater than or equal to 120), average (IQ between 80 and 119), and low intelligence (IQ less than or equal to 79). A favorable parental social and educational background was the best correlate of superior intelligence in the children. Larger head size from 1 year of age was an early finding associated with superior intelligence. Greater height and weight, from 4 years of age were later findings. Correlations between psychological performance at ages 4 and 7 years were statistically significant. Perinatal factors and medical complications did not affect the intellectual status of children with superior intelligence.
***
B/ Recherches ne trouvant pas de corrélations entre taille du cerveau (ou de certaines parties du cerveau) et intelligence.
Proc Natl Acad Sci U S A. 2000 Apr 25;97(9):4932-7.
Brain size does not predict general cognitive ability within families.
Schoenemann PT, Budinger TF, Sarich VM, Wang WS.
Department of Anthropology, University of Pennsylvania, Philadelphia, PA 19104-6398, USA.
mailto:ptschoen@sas.upenn.edu
Hominid brain size increased dramatically in the face of apparently severe associated evolutionary costs. This suggests that increasing brain size must have provided some sort of counterbalancing adaptive benefit. Several recent studies using magnetic resonance imaging (MRI) have indicated that a substantial correlation (mean r = approximately 0.4) exists between brain size and general cognitive performance, consistent with the hypothesis that the payoff for increasing brain size was greater general cognitive ability. However, these studies confound between-family environmental influences with direct genetic/biological influences. To address this problem, within-family (WF) sibling differences for several neuroanatomical measures were correlated to WF scores on a diverse battery of cognitive tests in a sample of 36 sibling pairs. WF correlations between neuroanatomy and general cognitive ability were essentially zero, although moderate correlations were found between prefrontal volumes and the Stroop test (known to involve prefrontal cortex). These findings suggest that nongenetic influences play a role in brain volume/cognitive ability associations. Actual direct genetic/biological associations may be quite small, and yet still may be strong enough to account for hominid brain evolution.
Neurology. 1998 May;50(5):1246-52.
Brain size, head size, and intelligence quotient in monozygotic twins.
Tramo MJ, Loftus WC, Stukel TA, Green RL, Weaver JB, Gazzaniga MS.
Department of Neurobiology, Harvard Medical School, Massachusetts General Hospital, Boston 02115, USA.
Many studies of monozygotic (MZ) twins have revealed evidence of genetic influences on intellectual functions and their derangement in certain neurologic and psychiatric diseases afflicting the forebrain. Relatively little is known about genetic influences on the size and shape of the human forebrain and its gross morphologic subdivisions. Using MRI and quantitative image analysis techniques, we examined neuroanatomic similarities in MZ twins and their relationship to head size and intelligence quotient (IQ). ANOVA were carried out using each measure as the dependent variable and genotype, birth order, and sex, separately, as between-subject factors. Pairwise correlations between measures were also computed. We found significant effects of genotype but not birth order for the following neuroanatomic measures: forebrain volume (raw, p < or = 0.0001; normalized by body weight, p = 0.0003); cortical surface area (raw, p = 0.002; normalized, p = 0.001); and callosal area (raw, p < or = 0.0001; normalized by forebrain volume, p = 0.02). We also found significant effects of genotype but not birth order for head circumference (raw, p = 0.0002; normalized, p < or = 0.0001) and full-scale IQ (p = 0.001). There were no significant sex effects except for raw head circumference (p = 0.03). Significant correlations were observed among forebrain volume, cortical surface area, and callosal area and between each brain measure and head circumference. There was no significant correlation between IQ and any brain measure or head circumference. These results indicate that: 1) forebrain volume, cortical surface area, and callosal area are similar in MZ twins; and 2) these brain measures are tightly correlated with one another and with head circumference but not with IQ in young, healthy adults.
Can J Psychol. 1991 Dec;45(4):507-22.
Sex differences in human brain size and the general meaning of differences in brain size.
Peters M.
Dept. Psychology, University of Guelph, Ontario, Canada.
Contrary to commonly held convictions, there is no clear association between brain size and body parameters in humans. Within sexes, once age and health status are controlled for, there is no significant association between brain size and body height for females. For males, body height accounts for no more than .04% of the variance in brain size. The relation between brain weight and body weight is even less clearly defined. Nevertheless, there are large and significant differences in brain size between the sexes. If no adequate body parameters can be found that scale to brain size within the sexes, the marked dimorphism between males and females makes it even more difficult to find a common set of parameters that allow evaluation of brain size differences between sexes. Within and across sexes, there is no convincing link between a limited measure of behavioural capacity (IQ) and brain size. This leads to the more general question: Why would one expect such a link, and, if it is not found, what does this mean in the context of general theories of cortical function?