Sex Differences In Brain Size Research Articles

Morphometric Evaluation of the Human Corpus Callosum using Magnetic Resonance Imaging: Sex Difference and Relationship to Age and Intracranial Size

Introduction: The objective of this study was to determine the normal values of corpus callosum (CC) subregions in healthy adult individuals in our population using magnetic resonance imaging (MRI) and to reveal gender differences during normal aging. Material and Methods: We performed the measurements of certain CC dimensions in 104 (44 males and 60 females) individuals. MRI imaging device was used for the measurements. The subregions of CC were measured with the midsagittal images. After the measurements of CC and its sections’ (rostrum [R], genus [G], anterior body, posterior body, isthmus [I], and splenium [S]), length (L), width (W), and area (A) were carried out, the intracranial volume (ICV) and intracranial area (ICA) values were calculated. The Student’s t-test and Pearson correlation test were used for statistical analysis. Results: Morphometric data of length, width, area, ICV, and ICA were collected. No significant difference was identified in CC morphometry by age among the patients (P > 0.05). Indicating longer diameters in males, the differences between the genders were significant (P < 0.05). Moreover, the mean of R-L, G-A, and G-W measurements was found significant between the age groups (P < 0.001). Conclusion: Sexual dimorphism in the CC is not a simple artifact of sex differences in brain size and may reflect differences in connectivity necessitated by differences in brain sizes.

Carriage of Supernumerary Sex Chromosomes Decreases the Volume and Alters the Shape of Limbic Structures.

Sex chromosome aneuploidy (SCA) increases risk for several psychiatric disorders associated with the limbic system, including mood and autism spectrum disorders. Thus, SCA offers a genetics-first model for understanding the biological basis of psychopathology. Additionally, the sex-biased prevalence of many psychiatric disorders could potentially reflect sex chromosome dosage effects on brain development. To clarify how limbic anatomy varies across sex and sex chromosome complement, we characterized amygdala and hippocampus structure in a uniquely large sample of patients carrying supernumerary sex chromosomes (n = 132) and typically developing controls (n = 166). After adjustment for sex-differences in brain size, karyotypically normal males (XY) and females (XX) did not differ in volume or shape of either structure. In contrast, all SCAs were associated with lowered amygdala volume relative to gonadally-matched controls. This effect was robust to three different methods for total brain volume adjustment, including an allometric analysis that derived normative scaling rules for these structures in a separate, typically developing population (n = 79). Hippocampal volume was insensitive to SCA after adjustment for total brain volume. However, surface-based analysis revealed that SCA, regardless of specific karyotype, was consistently associated with a spatially specific pattern of shape change in both amygdala and hippocampus. In particular, SCA was accompanied by contraction around the basomedial nucleus of the amygdala and an area crossing the hippocampal tail. These results demonstrate the power of SCA as a model to understand how copy number variation can precipitate changes in brain systems relevant to psychiatric disease.

Sex differences in brain size and general intelligence (g)

Utilizing MRI and cognitive tests data from the Human Connectome project (N=900), sex differences in general intelligence (g) and molar brain characteristics were examined. Total brain volume, cortical surface area, and white and gray matter correlated 0.1–0.3 with g for both sexes, whereas cortical thickness and gray/white matter ratio showed less consistent associations with g. Males displayed higher scores on most of the brain characteristics, even after correcting for body size, and also scored approximately one fourth of a standard deviation higher on g. Mediation analyses and the Method of Correlated Vectors both indicated that the sex difference in g is mediated by general brain characteristics. Selecting a subsample of males and females who were matched on g further suggest that larger brains, on average, lead to higher g, whereas similar levels of g do not necessarily imply equal brain sizes.

Individual differences in the dominance of interhemispheric connections predict cognitive ability beyond sex and brain size

Global structural brain connectivity has been reported to be sex-dependent with women having increased interhemispheric connectivity (InterHc) and men having greater intrahemispheric connectivity (IntraHc). However, (a) smaller brains show greater InterHc, (b) larger brains show greater IntraHc, and (c) women have, on average, smaller brains than men. Therefore, sex differences in brain size may modulate sex differences in global brain connectivity. At the behavioural level, sex-dependent differences in connectivity are thought to contribute to men-women differences in spatial and verbal abilities. But this has never been tested at the individual level. The current study assessed whether individual differences in global structural connectome measures (InterHc, IntraHc and the ratio of InterHc relative to IntraHc) predict spatial and verbal ability while accounting for the effect of sex and brain size. The sample included forty men and forty women, who did neither differ in age nor in verbal and spatial latent components defined by a broad battery of tests and tasks. High-resolution T1-weighted and diffusion-weighted images were obtained for computing brain size and reconstructing the structural connectome. Results showed that men had higher IntraHc than women, while women had an increased ratio InterHc/IntraHc. However, these sex differences were modulated by brain size. Increased InterHc relative to IntraHc predicted higher spatial and verbal ability irrespective of sex and brain size. The positive correlations between the ratio InterHc/IntraHc and the spatial and verbal abilities were confirmed in 1000 random samples generated by bootstrapping. Therefore, sex differences in global structural connectome connectivity were modulated by brain size and did not underlie sex differences in verbal and spatial abilities. Rather, the level of dominance of InterHc over IntraHc may be associated with individual differences in verbal and spatial abilities in both men and women.

Why size matters: Differences in brain volume account for apparent sex differences in callosal anatomy: The sexual dimorphism of the corpus callosum

Numerous studies have demonstrated a sexual dimorphism of the human corpus callosum. However, the question remains if sex differences in brain size, which typically is larger in men than in women, or biological sex per se account for the apparent sex differences in callosal morphology. Comparing callosal dimensions between men and women matched for overall brain size may clarify the true contribution of biological sex, as any observed group difference should indicate pure sex effects. We thus examined callosal morphology in 24 male and 24 female brains carefully matched for overall size. In addition, we selected 24 extremely large male brains and 24 extremely small female brains to explore if observed sex effects might vary depending on the degree to which male and female groups differed in brain size. Using the individual T1-weighted brain images (n=96), we delineated the corpus callosum at midline and applied a well-validated surface-based mesh-modeling approach to compare callosal thickness at 100 equidistant points between groups determined by brain size and sex. The corpus callosum was always thicker in men than in women. However, this callosal sex difference was strongly determined by the cerebral sex difference overall. That is, the larger the discrepancy in brain size between men and women, the more pronounced the sex difference in callosal thickness, with hardly any callosal differences remaining between brain-size matched men and women. Altogether, these findings suggest that individual differences in brain size account for apparent sex differences in the anatomy of the corpus callosum.

Mental Rotation Test Performance in Four Cross-Cultural Samples (N = 3367): Overall Sex Differences and the Role of Academic Program in Performance

Two meta-analyses (Linn and Petersen, 1985; Voyer et al., 1995) discuss variables that affect mental rotation performance but they do not mention a potentially important variable, the Academic Program in which students are enrolled. Sex differences in brain size have been related to sex differences in spatial performance (e.g., Falk et al., 1999) and thus it is important to know whether mental rotation performance shows a significant interaction between Sex and Academic Program. To put our understanding of the Academic Program effect on a firmer empirical footing, we conducted a large scale multicultural study, with samples from Canada, Germany and Japan, using identical test procedures in all studies. Significant main effects for Sex and Academic Program were found in all four studies, with large effect sizes for Sex and medium to large effect sizes for Academic Program (based on Cohen's d). No significant interactions between these variables were found in the four samples. Our demonstration of a reliable Academic Program effect has clear and important pragmatic implications for a broad range of work on spatial ability and its interpretation.

Sex differences in corpus callosum size: relationship to age and intracranial size.

This quantitative MRI study reports measurement of corpus callosum area taken from midsagittal brain images in 51 healthy men and 41 healthy women, spanning the adult age range (22 to 71 years). Men had larger brains and corpora callosa than women, but callosal size did not correlate with age in either sex. Intracranial (i.c.) volume (ICV) and midsagittal i.c. area (ICA) of brain were used in covariate, regression, and ratio analyses to determine whether sex differences in the corpus callosum endured with statistical adjustment for sex differences in maximally attained brain size. With the exception of one ratio measure, the different statistical adjustments for the contribution of sex differences in brain size to corpus callosum size all indicated that men had larger corpora callosa than women for their brain size. A subsample of men and women selected to be matched on i.c. volume and age confirmed this statistical observation. Sexual dimorphism in the corpus callosum is not a simple artifact of sex differences in brain size and may reflect differences in connectivity necessitated by differences in brain size.

Sex differences in brain size, stature and intelligence in children and adolescents: some evidence from Estonia

Abstract Sex differences in brain size and stature decrease from the age of 7 through 13–14 years and increase from the age of 15 through 18 years in Estonia, as they do in the United States. Sex differences in intelligence show a somewhat similar decrease and increase although they do not move precisely in synchrony with the morphological trends. The results are interpreted as suggesting that sex differences in maturation determine the magnitude of sex differences in physical and mental development during childhood and adolescence.

Sex differences in brain size and mental abilities: comments on R. Lynn and D. Kimura

Herein, I 1. (1) show that Lynn ( Personality and Individual Differences, 17, 257–271, 1994) somewhat misinterpreted my hypothesis that the relatively larger brains of men are related to their, on average, superior spatial and mathematical reasoning abilities, 2. (2) argue that Lynn's findings strongly support this hypothesis, and 3. (3) suggest that Kimura ( Personality and Individual Differences, 17, 53–60, 1994) ‘missed the obvious’ while attempting to explain sex differences in spatial (and other) abilities.

Corrections to a paper on race and sex differences in brain size and intelligence

This paper presents two corrections to an earlier paper by Rushton ( Personality and Individual Differences, 11, 785–794, 1990). The first is to the equation used to calculate cranial capacities from externally measured head sizes. Eleven millimeters should be subtracted from head length and width for fat and skin around the skull. When the subtractions are made the cranial capacities for the different races are about 200 cm 3 smaller than previously reported, although the significant rank ordering of Mongoloids > Caucasoids > Negroids is preserved. The second correction is to the statement that there are no sex differences in brain size when body size variables are controlled. Two recent studies using large data sets show that after covariance adjustment for body size, women's brains average 100 g lighter and 110 cm 3 smaller than men's. These findings are best understood from the perspective of human evolution.

RETRACTED: Race, Brain Size, and Intelligence: A Reply to Cernovsky

Cernovsky's 1990 critique of my work on the relation between brain size and IQ inadequately presents my position. I did not address the issue of sex differences in brain size nor did I conclude that "women are less intelligent than men" (p. 337). In the autopsy study cited by Cernovsky, it was concluded that, when body size is controlled, the male-female difference in brain size is removed but the black-white difference in brain size remains. Cernovsky also ignores much additional data, including that Mongoloid populations have larger and heavier brains than Caucasoids. Here, I review evidence on the relation between (a) brain size and race and (b) brain size and intelligence. Data are also tabulated for personality, speed of maturation, and sexuality, on all of which the Caucasoid average consistently falls between those of Mongoloids and Negroids. This ordering may be explained by a gene-based evolutionary theory of r/K reproductive strategies in which Mongoloids are more K-selected than Caucasoids and Caucasoids more than Negroids.

Race, brain size and intelligence: A rejoinder to Cain and Vanderwolf

Cain and Vanderwolf ( Personality and Individual Differences 11, pp. 777–784, 1990) commit a Grand Type II Error in denying the relation between the variables juxtaposed in the title of this rejoinder. This reply (a) presents 20 studies showing a positive correlation between brain size and IQ, one of which used magnetic resonance imaging to scan the brain, (b) re-examines whether the races differ in brain size from data not previously presented including a reanalysis of a 1930 study using external head measurements and a 1984 study of endocranial volume and confirms that the ranking is Mongoloids &62; Caucasoids &62; Negroids, (c) suggests that when the appropriate brain-body allometric regressions are taken into account, sex differences in brain size disappear while race differences remain, and (d) explains the evolution of brain size, intelligence and race from a broad-based r / K life-history perspective.

Brain stem auditory, pattern-reversal visual, and short-latency somatosensory evoked potentials: Latencies in relation to age, sex, and brain and body size

To determine standards of normality for auditory, somatosensory and visual evoked potentials commonly used in the assessment of neurological disease, 8 AEP, 1 VEP and 12 SEP components were recorded to stimulation of left and right ears, eyes, and median nerves in 286 normal subjects ranging in age from 4 to 95 years. Peak and interpeak latencies, and left-right differences in latency, were analyzed as a function of age, sex, and estimates of brain and body size. Major features of the results were: (1) Peak latencies of all components showed statistically significant increases in latency with age except that VEP P100 latency decreased significantly between 4 and 19 years and did not change between 20 and 59 years. (2) In adults the peak latencies of all components were significantly later in males than in females. For AEPs and VEPs these differences were explained by sex differences in brain size, and for adult SEPs were explained by sex differences in arm and shoulder dimensions. No significant sex differences in VEP and SEP latencies were seen in children. (3) Most interpeak latencies showed significant differences in relation to age or sex. (4) Age and sex are useful predictors of latency for nearly all peak and interpeak latencies; in addition, height is a useful predictor of SEP peak latencies. (5) Left-right latency differences showed little age-related, and no sex-related, change. The interlaboratory use of these or other normative data was discussed. It was concluded that these AEP and SEP norms can probably be used in other laboratories if stimulating and recording conditions are similar. However, VEP results are diffcult to transfer due to the poorly understood effects of variation in stimulus conditions. Some issues regarding the optimal characterization of norms were also discussed.

Functionalism, Darwinism, and the psychology of women.

Examines the psychology of women as it was studied from the middle of the 19th century to the 1st 3rd of the 20th century. During that period 3 topics received the most attention: sex differences in brain size and complexity and their implications for cognitive and affective behavior; the hypothesis of greater male variability (a corollary of evolutionary theory) and its social implications; and the expression of maternal instinct. Each topic is examined in relation to evolutionary theory and its influence on the conduct of 19th century science. The antecedents of each topic are traced as is the subsequent redefinition of each within the paradigm of behaviorism. It is proposed that each of these topics functioned as scientific myth which justified and explained contemporary cultural values. (71 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)