Swaab D F, Gooren L J, Hofman M A
Netherlands Institute for Brain Research, Amsterdam.
J Homosex. 1995;28(3-4):283-301. doi: 10.1300/J082v28n03_07.
Recent brain research has revealed structural differences in the hypothalamus in relation to biological sex and sexual orientation. Differences in size and cell number of various nuclei in the hypothalamus for homosexual versus heterosexual men have recently been reported in two studies. We have found that a cluster of cells in the preoptic area of the human hypothalamus contains about twice as many cells in young adult men as in women. We have called this cluster the sexually dimorphic nucleus (SDN). The magnitude of the difference is the SDN depends on age. In other human research, two other hypothalamic nuclei (interstitial nuclei of the anterior hypothalamus [INAH] 2 and 3) and part of the bed nucleus of the stria terminalis (BST) have been reported to be sexually dimorphic in the human. Sexual differentiation to the human brain takes place much later than originally claimed. At birth the SDN contains only some 20% of the cells found at 2 to 4 years of age. The cell number rapidly increases in boys and girls at the same rate until 2 to 4 years of age. After that age period, a decrease in cell number takes place in girls, but not in boys. This causes the sexual differentiation of the SDN. This postnatal period of hypothalamic differentiation indicates that, in addition to genetic factors, a multitude of environmental and psychosocial factors may have profound influence on the sexual differentiation of the brain. No difference in SDN cell number was observed between homosexual and heterosexual men. This finding refutes Dörner's hypothesis that homosexual males have a "female" hypothalamus. However, in a sample of brains of homosexual men we did find that an area of the hypothalamus called the suprachiasmatic nucleus (SCN) contains twice as many cells as the SCN of a heterosexual group. A recent report by LeVay claims that another nucleus, INAH-3, is more than twice as large in heterosexual as in homosexual men, whereas Allen and Gorski found that the anterior commissure was larger in homosexual men than in heterosexual men or women. Preliminary research on male-to-female transsexuals is also discussed. The functional implications of these findings in determining adult sexual orientation are as yet far from clear.
近期的脑部研究揭示了下丘脑在生物学性别和性取向方面的结构差异。两项研究最近报道了同性恋男性与异性恋男性下丘脑各核团在大小和细胞数量上的差异。我们发现，人类下丘脑视前区的一组细胞在年轻成年男性中的数量约为女性的两倍。我们将这组细胞称为性二态核（SDN）。SDN中差异的程度取决于年龄。在其他人体研究中，据报道人类下丘脑的另外两个核团（下丘脑前间质核[INAH]2和3）以及终纹床核（BST）的一部分具有性别二态性。人类大脑的性别分化比最初认为的要晚得多。出生时，SDN中的细胞数量仅约为2至4岁时的20%。在2至4岁之前，男孩和女孩的细胞数量以相同的速度快速增加。在那个年龄阶段之后，女孩的细胞数量会减少，而男孩不会。这导致了SDN的性别分化。下丘脑分化的这个出生后阶段表明，除了遗传因素外，许多环境和社会心理因素可能对大脑的性别分化产生深远影响。在同性恋男性和异性恋男性之间未观察到SDN细胞数量的差异。这一发现反驳了多纳的假设，即同性恋男性有一个“女性化”的下丘脑。然而，在一组同性恋男性的大脑样本中，我们确实发现下丘脑的一个称为视交叉上核（SCN）的区域所含细胞数量是异性恋组SCN的两倍。利维的一份近期报告称，另一个核团INAH - 3在异性恋男性中的大小是同性恋男性的两倍多，而艾伦和戈尔斯基发现同性恋男性的前连合比异性恋男性或女性的更大。文中还讨论了对男变女变性者的初步研究。这些发现在确定成人性取向方面的功能意义目前还远不清楚。
