Peper Jiska S, Brouwer Rachel M, van Baal G Caroline M, Schnack Hugo G, van Leeuwen Marieke, Boomsma Dorret I, Kahn René S, Hulshoff Pol Hilleke E
Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Center, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
Eur J Endocrinol. 2009 May;160(5):739-46. doi: 10.1530/EJE-08-0915. Epub 2009 Feb 13.
Brain volume of boys is larger than that of girls by approximately 10%. Prenatal exposure to testosterone has been suggested in the masculinization of the brain. For example, in litter-bearing mammals intrauterine position increases prenatal testosterone exposure through adjacent male fetuses, resulting in masculinization of brain morphology.
The influence of intrauterine presence of a male co-twin on masculinization of human brain volume was studied in 9-year old twins.
Magnetic resonance imaging brain scans, current testosterone, and estradiol levels were acquired from four groups of dizygotic (DZ) twins: boys from same-sex twin-pairs (SSM), boys from opposite-sex twin-pairs (OSM), girls from opposite-sex twin-pairs (OSF), and girls from same-sex twin-pairs (SSF; n=119 individuals). Data on total brain, cerebellum, gray and white matter volumes were examined.
Irrespective of their own sex, children with a male co-twin as compared to children with a female co-twin had larger total brain (+2.5%) and cerebellum (+5.5%) volumes. SSM, purportedly exposed to the highest prenatal testosterone levels, were found to have the largest volumes, followed by OSM, OSF and SSF children. Birth weight partly explained the effect on brain volumes. Current testosterone and estradiol levels did not account for the volumetric brain differences. However, the effects observed in children did not replicate in adult twins.
Our study indicates that sharing the uterus with a DZ twin brother increases total brain volume in 9-year olds. The effect may be transient and limited to a critical period in childhood.
男孩的脑容量比女孩大约大10%。有研究表明，产前暴露于睾酮会使大脑男性化。例如，在多胎哺乳动物中，子宫内的位置会通过相邻的雄性胎儿增加产前睾酮暴露，从而导致脑形态的男性化。
在9岁的双胞胎中研究了男性同卵双胞胎的子宫内存在对人类脑容量男性化的影响。
从四组异卵（DZ）双胞胎中获取磁共振成像脑部扫描、当前睾酮和雌二醇水平：同性双胞胎对中的男孩（SSM）、异性双胞胎对中的男孩（OSM）、异性双胞胎对中的女孩（OSF）和同性双胞胎对中的女孩（SSF；n = 119人）。检查了全脑、小脑、灰质和白质体积的数据。
无论自身性别如何，与有女性同卵双胞胎的儿童相比，有男性同卵双胞胎的儿童的全脑（+2.5%）和小脑（+5.5%）体积更大。据推测，SSM暴露于最高的产前睾酮水平，其脑容量最大，其次是OSM、OSF和SSF儿童。出生体重部分解释了对脑容量的影响。当前的睾酮和雌二醇水平不能解释脑容量的差异。然而，在儿童中观察到的影响在成年双胞胎中并未重现。
我们的研究表明，与异卵双胞胎兄弟共用子宫会增加9岁儿童的全脑容量。这种影响可能是短暂的，并且仅限于儿童期的关键时期。
