跨性别者的大脑与顺性别者的大脑不一样吗?

跨性别者的大脑与顺性别者的大脑不一样吗?

针对性别认定的生物学基础的研究工作尚处于初级阶段,但一些线索正在开始浮现。

2018年3月1日,《科学家》

作者:SHAWNA WILLIAMS

译者:@San若梦

近年来,由于诸如Caitlyn Jenner和Laverne Cox等名人正在成为一个边缘化群体中能被识别的面孔,美国社会对跨性别者的认知已经看见了海量的变化。跨性别者权益也已成为一个主流的政治议题,而人们在被提及时应该使用他们认为最合适的名字和人称代词——不管这些指定名称是否与其出生证上的相吻合或是与男性和女性的分类相一致——的观念正在被接受。

但是对于跨性别者出生性别和性别认定相差异的生物学意义上的理解仍然不得而知。近年来诸如功能性磁共振成像【functional magnetic resonance imaging (fMRI)】一类的技术已经开始得出一些对于这种被称为性别焦虑的状态在生物学上可能的构成基础的线索,特别是研究者们正在鉴定的跨性别和顺性别个体的大脑在结构及功能的不同层面的相似性和差异性,可能对解释一个人所认定的性别与其出生时的性别并不相配的坚定信念会有所助益。

诸如功能性磁共振成像【functional magnetic resonance imaging (fMRI)】一类的技术已经开始得出一些对于性别在生物学上可能的构成基础的线索

这些结果可能对于如何诊断及治疗性别焦虑并不会产生多大影响,在阿姆斯特丹自由大学医学院(VU University Medical Center in Amsterdam)研究性别不一致的 Baudewijntje Kreukels 说明道,“很重要的一点是不能被看作这样,‘当你在大脑里看见了「性别焦虑」,那就是真的。’”但是来自于这些研究的深刻见解可能对于满足一些跨性别者理解自身状态的根源的愿望会有很大助益,她补充道,“如此一来,能够发现他们与出生时被指定性别的差异是否是其大脑中什么度量的反映就太好了。”

性与性别之间的发育性不相配?

关于性别焦虑的基础有一个很重要的假说是,在子宫里生殖器的性分化与大脑的性分化是各自独立发生的,这使得身体朝着一个方向而意识朝着另一个方向成为可能。这个构想的基础是这样一种观念,那就是性别本身——一个人属于哪个类别的意识,而非其生物性别——对人类来说在子宫里就决定了。这个观点并非一直是科学上的共识,近到上世纪八十年代还有许多研究者争论说,仅仅是我们如何养育孩子的社会规范在决定着女孩和男孩之间发育出的行为差异。

在这条思路(意指社会规范论——译者注)上最著名的倡导者也许是心理学家John Money,他甚至假设一个长着先天性异常阴茎或是在外科事故中失去阴茎的男婴,能够在手术和激素治疗后成功地被当作女性养育成人。但是Money的案例中至少有一起在此行为过程中很明显产生了适得其反的结果:当事人在青少年时期回复到以男人身份生活,之后自杀了(此案例当事人名为David Reimer——译者注)。大脑中的性分化现在已有良多记载,虽然其多大程度是基于生物性或社会因素这点正在被激烈地争论着。

发育性不相配观点得到两个系列发现的支持。动物研究显示出在子宫里,生殖器和大脑是在发育的不同阶段获得阳刚或阴柔的特征,因而导致激素波动或是别的一些因素将那些器官置于不同轨迹的潜在可能。(参见“大脑中的性分化”,《科学家》,2015年10月)而人类研究则发现,在大脑的好几个区域里跨性别者和那些与他们认定性别相同的顺性别者比和那些与他们出生性别相同的顺性别者具有更大的相似度。(比如,出生性别为男性但认定性别为女性的跨性别者,与一位顺性别女性的相似度,高于与一位出生性别为男性者的相似度。——译者注)

荷兰神经科学院(Netherlands Institute for Neuroscience)的Dick Swaab 是一位在性别认定所潜在的神经科学方面的先驱者。1990年代中期他的团队检查了六位跨性别女性死后的大脑并且报告说,纹状体床核【bed nucleus of the stria terminalis (BSTc or BNSTc)】——前脑上一个在性方面具双相性且已知对性行为很重要的区域——中心区的大小与顺性别女性比与顺性别男性更为接近。2一个尸检大脑的后续研究也发现在纹状体床核的某类特定神经元的数目,跨性别女性与其顺性别对应者——以及一个跨性别男性与顺性别男性——之间的相似性。3这些差异看起来并不能归咎于内分泌的性激素功能或是成年后的激素治疗的影响。在发表于2008年的另一项研究中,Swaab和一位合作者在尸检中检查了INAH3亚核——下丘脑中生前与性取向相关联的一个区域——的容量,这些研究者们发现顺性别男性的该区域大约是无论跨性别还是顺性别女性的两倍。4

而且并非仅仅是大脑结构显示出跨性别个体跟那些与其认定性别相同的个体比跟那些与其出生性别相同的个体更为接近。在由阿姆斯特丹自由大学医学院和位于阿姆斯特丹的荷兰神经科学院的 Julie Bakker领军的一项在空间推理任务中对神经系统的活动进行调查的研究中,跨性别者与其顺性别对应者在功能上的相似性很明显。以前的研究已表明男性和女性的运动由不同的大脑区域参与,Bakker及同事们发现跨性别男孩(还未接触过雄激素,但已被抑制过青春期雌激素)以及顺性别男孩都比顺性别女孩在执行任务时其额脑区表现出较小的反应。5

一些研究已经确定跨性别者大脑的特征处于两种性别的典型性特征之间

另外一些研究已经确定跨性别者大脑的特征处于两种性别的典型性特征之间——这些结果一般都被发育性不相配假说的倡导者视作对其观点的支持。比如在2014年,维也纳医科大学(Medical University of Vienna)的神经学家 Georg Kranz运用漫射式磁共振成像(diffusion MRI)的数据来调查跨性别和顺性别实验者的白质微结构。一种被称作平均扩散率(mean diffusivity)的对神经性属性的度量,顺性别女性水平最高,顺性别男性最低,跨性别男性和女性居于二者之间——虽然平均扩散率在生理学意义上代表着什么还未被完全理解。6“看起来似乎这些跨性别群体属于一种中间状态,” Kranz说道。对个体激素水平的控制并未改变群体之间的差异,导致作者们建议白质微结构其实在出生前及出生之初就已经被所处的激素环境决定了——虽然之后的生活经历也扮演了一个角色的可能性并不能被排除,他补充说道。

“所有已知的证据都指向一个生物性决定的认定,”Kranz说道,“在「跨性别」人们中你可以说雄激素环境在其身体的发育过程及大脑的发育过程中不相配,所以其身体被男性化而大脑被女性化了,反之亦然。”

对跨性别者大脑研究的不统一结果

然而不大可能发生的是,关于性别认定会有如此一个直截了当的生物性解释,而一些研究已经鉴定出跨性别者大脑中看起来与其出生性别更为接近的特征,导致对发育性不相配假说的怀疑。2015年荷兰神经科学院的一项研究中,将55位女-变-男和38位男-变-女的跨性别青少年大脑灰质的分布与其同年龄段的顺性别者对照组进行比较,发现跨性别实验者跟那些与其有相同出生性别的顺性别实验者在下丘脑和小脑部位具有着广泛的相似性,7然而在一些特定的亚区域还是有差异。

2013年一项集中于皮质厚度——女性倾向于稍大于男性——的研究也给出了不统一结果。由西班牙国家远程教育大学(National Distance Education University in Spain)的神经学家 Antonio Guillamon领军,研究者们对94位实验者的磁共振成像进行了分析,发现跨性别女性和男性总的的皮质厚度都更接近于顺性别女性甚于顺性别男性。但此项发现并非对整个大脑都如此:在前脑一个参与肌肉运动和学习、被称作右壳核的结构里,跨性别男性的皮质厚度与顺性别男性的更相似,而跨性别女性与两个顺性别对照组都未显示出明显的差别。8

“我们所发现的是,在好几个区域顺性别女性、男-变-女以及女-变-男的跨性别者都比顺性别男性的皮质更厚,但并不是在同一个区域,”Guillamon说道,并且在2016年的一篇评论文章里他假定说顺性别女性、跨性别女性、跨性别男性以及顺性别男性,各自都有不同的表现型。9“皮质对性别而言至关重要。”

在与发育性不相配假说相关的另一项给出不统一结果的研究中,德国亚琛工业大学(RWTH Aachen University in Germany)的研究者们测试了顺性别者与跨性别女性如何分辨男性和女性声音。这个团队发现在某些方面,比如一个被称作右额上回的大脑区域的激活水准,跨性别和顺性别女性相似,而顺性别男性显示出更高的活力——可能反应出其在此项任务上所作的感知努力。10仅管在激活水准上跨性别和顺性别女性相似,但跨性别女性在辨别男性和女性的声音上同样擅长,而两种顺性别者都发现辨别相反性别的声音更容易。

“总而言之,我们看见「跨性别者」在一些度量上的确显示出与其性别认定相同者的相似性,但并非对所有的度量都如此,”Kreukels说道。研究者们“还在试图弄清”大脑里的那些相似性和差异性,她说。

性别认定:一个复杂的现象

即使是产前的环境能够对身体和大脑稍微朝着不同方向推动,那可能也仅仅是潜于性别焦虑之下诸多作用力中的一个因素而已,Kreukels说道。她解释说这幅完整的图象可能是“生物性、心理性及社会性因素的综合——因为我们真地认为它是介于所有这些因素之间的一种复杂的相互作用,迄今的研究还未给出解决方案。”

瑞典卡罗林斯卡医学院(Karolinska Institutet in Sweden, KI) 的神经学家Ivanka Savic 也对发育性不相配假说的解释力很怀疑。“跨性别现象并非因为大脑的性别和身体的性别不平等所致那么简单,”她说道。比如在2011年Savic及一位同事发现跨性别女性的丘脑和壳核两个大脑区域比其顺性别对照组更小,但总的灰质容量又更大。11这些大脑区域在以前的研究中曾被显示出“调解关于身体的认知,”Savic说明道——比如在功能性磁共振成像(fMRI)研究中人们被出示他们自己和他人的照片,“焦虑就是对「自己」的身体不开心,每天早上都会感觉‘这是我的身体,但它不是我,’”她说道。

后续工作中Savic的团队开始探索功能性磁共振成像所展示的大脑神经系统并且发现“系统调解它自身与系统调解自己的身体——我的身体——之间的联结性,跨性别者更弱,”她解释道。具体说来就是与两种性别的顺性别个体相比,当跨性别男性在观看他们自己的形象时在被称作前扣带(anterior cingulate)、后扣带(posterior cingulate)及楔前叶(precuneus)等的区域显示出更少的联结性,而当图象被变形处理得看起来更为男性化时其前扣带与后两个区域的联结性增大。12

在解读所观察到的这些不同群组之间差异时的一个困难是,什么时候或为什么这些差异会发生仍不清楚,比利时根特大学(Ghent University in Belgium)心理学家 Sven Müller说道,并且报告说相互关联也许反应的并非随意的关系。关于性别不一致多大程度上具有生物性起因“我认为判决仍未定,”他说道。“大脑在成年时期可塑性极强,”他说明道,所以跨性别者和顺性别者之间被鉴定出的那些差异可能是、也可能不是从出生时就具有了。

这是生物学以及人类生物学的核心问题之一——Antonio Guillamon,西班牙国家远程教育大学

另外,那些探索性别焦虑生物学解释的科学家们还面临着后勤方面的挑战。要征集到足够多的跨性别实验者来进行具有高效统计意义的研究通常都很困难,但有些研究者正在努力补救此问题。比如在2017年,通过整合分析增进神经系统成像遗传学联合会(Enhancing Neuro Imaging Genetics through Meta Analysis, ENIGMA Consortium)——该组织致力于促进检测对大脑结构及功能产生适中基因影响的研究者们建立联系及分享信息——启动了一个新的、专注于跨性别现象的工作团队。范德堡大学(Vanderbilt University)遗传学家Lea Davis 正在组织一项尚待资助的努力,对上千位跨性别者和顺性别者进行基因组排序和分析,以寻找与性别认定相关联的变异。

除了关于性别认定的根源这个巨大的谜团之外,此领域的研究者们长期以来还有几个问题,比如对于那些经历变性过程,认定自身的二元化性别与其出生时的指定性别不同的人们,“我们仍然不知道男-变-女和女-变-男的变性欲是否属于同一种现象,或者「是否」你从两种性别出来一个相似的结果但其背后却有两种不同的机制,”一名德国亚琛工业大学的研究生以及一篇关于跨性别者大脑评论性文章的作者 Elke Smith说道。13另外一些出色的问题还包括,那些性取向不同的跨性别者,以及那些其性别焦虑在人生的早期就显示出来和那些在青少年或成年时才开始感觉焦虑的人们,他们的大脑有哪些——假如有任何的话——差别,Kreukels说道。另外还需确定的是,Savic补充道,那些在顺性别者和跨性别者之间已被确定的大脑上的差异是否在激素治疗之后仍然持续。(参见以下“激素治疗对大脑的影响”)

Guillamon建议道,更多的研究能够更进一步澄清不仅是性别焦虑同时也是性别本身的基础——通过远比我们认定的人称代词多得多的含意。“系统发生地同时与进化相关地很有必要知道一个人是男性或是女性,”并且与谁交配,他说道,“这是生物学以及人类生物学的核心问题之一。”

Savic说她希望这些对跨性别者的研究结果能够有助于使性别认定问题不再引发那么强烈的情绪,“这就是生物学的一部分,跟我有一头黑发而有些人却是红发一样。”

目前来说,正如人类经验的许多层面的状况一样,隐藏于性别之下的神经系统机制很大程度上还是个谜。尽管研究者们对顺性别者和跨性别者的一些大脑差异已做过记录,但一个关于性别的神经系统上的定义性标志还有待发现——也许它永远也不会被发现。但是随着一个可得性日益增长的强大的包括神经系统成像、基因组研究及别的工具在内的武器储备,研究者们肯定会对身分认定的这一基本层面获得更深刻的洞察。

参考书目

  1. A.-M. Bao, D.F. Swaab, “Sexual differentiation of the human brain: Relation to gender identity, sexual orientation and neuropsychiatric disorders,” Front Neuroendocrin, 32:214-26, 2011.

  2. J.-N. Zhou et al., “A sex difference in the human brain and its relation to transsexuality,” Nature, 378:68-70, 1995.

  3. F.P. Kruijver, “Male-to-female transsexuals have female neuron numbers in a limbic nucleus,” J Clin Endocrinol Metab, 85:2034-41, 2000.

  4. A. Garcia-Falgueras, D. Swaab, “A sex difference in the hypothalamic uncinate nucleus: relationship to gender identity,” Brain, 131:3132-46, 2008.

  5. S.M. Burke et al., “Male-typical visuospatial functioning in gynephilic girls with gender dysphoria—organizational and activational effects of testosterone,” J Psychiatry Neurosci, 41:395-404, 2016.

  6. G.S. Kranz et al., “White matter microstructure in transsexuals and controls investigated by diffusion tensor imaging,” J Neurosci, 34:15466-75, 2014.

  7. E. Hoekzema et al., “Regional volumes and spatial volumetric distribution of gray matter in the gender dysphoric brain,” Psychoneuroendocrino, 55:59-71, 2015.

  8. L. Zubiaurre-Elorza et al., “Cortical thickness in untreated transsexuals,” Cereb Cortex, 23:2855-62, 2013.

  9. A. Guillamon et al., “A review of the status of brain structure research in transsexualism,” Arch Sex Behav, 45:1615-48, 2016.

  10. J. Junger et al., “More than just two sexes: the neural correlates of voice gender perception in gender dysphoria,” PLOS ONE, 9:e111672, 2014.

  11. I. Savic, S. Arver, “Sex dimorphism of the brain in male-to-female transsexuals,” Cereb Cortex, 21:2525-33, 2011.

  12. J.D. Feusner et al., “Intrinsic network connectivity and own body perception in gender dysphoria,” Brain Imaging Behav, 11:964-76, 2017.

  13. E.S. Smith et al., “The transsexual brain—A review of findings on the neural basis of transsexualism,” Neurosci Biobehav R, 59:251-66, 2015.

更正(3月15日):这篇文章的初版里错误地表达说Lea Davis正在组织一项寻找与性别焦虑相关联的基因变异。我们已经对文章进行了修正以反应此事实——Davis是专注于遗传对性别认定的贡献的理解上,而非特定的性别焦虑。《科学家》对此差错表示遗憾。

译者注:1)参考书目的上标在文中始于【2】,应该是个编辑错误。我已发邮件给文章作者,假如收到回复会及时澄清。2)参考书目未作翻译,而是照录英文原文,以便于有志研究者检索、查验。

来源链接:

Are the Brains of Transgender People Different from Those of Cisgender People?

翻译:@San若梦

【申明:本人( @San若梦 )对在知乎所发《科普译文:跨性别者的大脑与顺性别者的大脑不一样吗?》保留一切权利,商业转载请与本人联系,非商业转载请注明出处。谢谢。】

发布于 2019-01-14 07:20

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最后由 @NaranMuuguu2023-11-19T14:25:33Z 编辑

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比较担心这会发展成另一种本质主义(

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欸 naran把那条回复删了?其实我不知道最近在论坛争吵了什么,我猜测是linca转发的那条由terf写的关于非二元讨论的那条,不过我对那篇文章觉得无聊,而且感觉会因此展开争论,于是就早早静音了那个话题(((

这个翻译的质量……令人感叹。

没记错的话,柠檬光上有篇关于 hrt and brain 帖子


另一篇,https://groups.io/g/MTFHRT/topic/79606271

edit: 那么,跨性别者的大脑…… - 脱水菜 - limelight


劳驾贴一下llt那篇?我没梯子

Raw

那么,跨性别者的大脑……

公开区 脱水菜

namenomonster (苏暖暖)April 5, 2021, 9:37pm#1


一点思考。这是一个有争议的研究领域,有许多互相矛盾的结果,目前尚无定论。这方面的讨论和影响非常复杂,比如此类结果给了跨性别合法性和去病化的依据,因此对改善群体医疗状况有相当大的意义;但另一方面,对自由意志、社会建构等是一个不利的证据,也阻碍了去性别化、拒绝性别标签与特质绑定这方面的主张推行。
我长时间以来会害怕这个结果真的成为铁证,不是因为“它能断言我不是女性或者不能成为女性”,就好像如果我不是青蛙,我也不会有成为青蛙的强烈愿望。我更多恐惧的是,“我没有掌握某些‘性别天赋’的可能——我是残次品”,以及“根据性别划分出圈层非常合理——我会被某些群体拒绝和排斥”。这相当于性别本质主义重新给我套上锁链,而这种焦虑需要通过正面的理论解析和实践尝试来破解而非绕过,否则依然很难建立自我认同和自我接纳,也无法治愈社交自信上的一道巨大创伤。

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Crystal.Wang (天文摄影师 有机实验实习 天文奥赛党 170以下)April 5, 2021, 10:26pm#2

“correlation doesn’t means causation”

9 Likes

namenomonster (苏暖暖)April 5, 2021, 10:44pm#3

的确,背后的具体逻辑关系很可能相当错综复杂
所以现在还是以脚踏实地改变自己为主

4 Likes

namenomonster (苏暖暖)April 5, 2021, 10:46pm#5

那个,虽然我无权干涉你发什么内容
但是在我的帖子回复我明显无法理解的信息,我会困扰的

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竹竹竹竹子 (竹竹竹竹子)April 6, 2021, 3:23am#6

居然能在这里看到楼子哥我好欣慰呜呜呜x

2 Likes

namenomonster (苏暖暖)April 6, 2021, 5:44am#7

刚才加他们群了,群聊的结果比较失望

2 Likes

NekoyamaS (猫山S)April 6, 2021, 6:26am#8

IMG_20210406_140745

很奇怪的是我发现他引用的那个文献没有提到MtF的大脑皮质问题,全文都只是将FtM和M/F志愿者做对比

4 Likes

竹竹竹竹子 (竹竹竹竹子)April 6, 2021, 6:14am#9

他们那个群确实……楼子哥一百多粉的时候我进去的,时间长了感觉群里气氛很怪我就出来了……就 别的vup群我也加了,都没有那种我看不懂/不理解/没法加入的感觉x

namenomonster (苏暖暖)April 6, 2021, 6:16am#10

确实说话不是很能对得上节奏,我也暂时收群助手了
不过与孟哥本人对话好像没什么问题,普通的好人(

1 Like

namenomonster (苏暖暖)April 6, 2021, 6:25am#11

感谢查阅原文!所以这个方面的结果确实非常有争议
还有下次记得,图片和文字之间留一个回车,最好现在也编辑一下

3 Likes

NekoyamaS (猫山S)April 6, 2021, 6:28am#12

好的谢谢提醒,已更改

1 Like

namenomonster (苏暖暖)April 6, 2021, 6:40am#13

谢谢~辛苦啦

1 Like

huamurui (木瑞)April 6, 2021, 7:11am#14

那普通的男女大脑…不是也有差异吗。。。

1617691998100

就算有,那种统计学上的规律在个体上可能……没那么大影响的!
“就好像大脑性别差异,当你以为是大脑差异就是导致男孩喜欢蓝色,女孩喜欢粉色的时候,你其实就已经偏离了科学的道路了——神经学只是强调了差异,但是还没能解释这些差异与行为的关系 。”
原文链接男性大脑和女性大脑有什么样的区别? - 知乎
好了,神经科学现在还没有那么强,给不出什么有实际意义的判断

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namenomonster (苏暖暖)April 6, 2021, 8:06am#15

所以之前我就在想一个很危险的命题
“人的性别是钉死的不能自己决定,只不过判断标准从生殖器变成大脑结构”
根据和大家的讨论,这个命题应该是错的,谢谢~

4 Likes

M (陸間)April 6, 2021, 8:33am#17

小时候就觉得粉色挺好看的,然后因为说小女孩才喜欢,所以强迫自己把这部分藏了下去,喜欢蓝色,不过也是那种比较浅的,天蓝之类的

现在放开了,粉色和蓝色都超棒!粉蓝超好看!

9 Likes

moe_rikaApril 6, 2021, 8:37am#18

吃药会改变认知功能

PubMed Central (PMC)

Health considerations for transgender women and remaining unknowns: a…

Transgender (trans) women (TW) were assigned male at birth but have a female gender identity or gender expression. The literature on management and health outcomes of TW has grown recently with more publication of research. This has coincided with…

The brain and cognition

Recent studies have investigated baseline differences between the brains of trans versus cis individuals as well as the effect of GAHT on the brain and cognition. The white matter microstructure of TW prior to initiation of GAHT has been characterized by diffusion tensor imaging to be between control females and control males.222225 Hahn and colleagues226 also described different structural connectivity networks in 21 TW prior to initiating GAHT compared with control females and males. Seiger and colleagues227 analyzed brain MRIs of 14 TW (mean age 26.9 ± 6.1 years) at baseline and after at least 4 months (169 days ± SD 38 days) of continuous oral or transdermal oestradiol and anti-androgens (cyproterone acetate ± GnRHa ± finasteride) and found decreases in the hippocampal region, increases in the ventricles and a correlation between progesterone levels and changes in grey matter structure. Mueller and colleagues228 found neuroanatomical volume differences in the amygdala, putamen and corpus callosum in TW compared with cis women but not cis men, suggesting the possibility of localized influence of sex hormones on neuroanatomy. These studies suggest there are hormonal influences on cortical and subcortical structures related to cognition, memory and emotional processing. Reviews stress that additional short- and long-term studies are needed to better understand the role of sex hormones on the adult human brain structure and function and how they relate to psychological differences between females and males.229,230

Brain-derived neurotrophic factor (BDNF) is involved in neurogenesis, neuronal maturation and synaptogenesis, influencing brain plasticity. A study of 10 TW from Belgium showed a significant decrease in BDNF levels after 12 months of GAHT (p = 0.014) independent of age, weight, BMI, total fat mass, total lean mass, LH, FSH, oestradiol, testosterone, cortisol, physical activity or smoking.231 Therefore, it was concluded that the decreased BDNF in TW after GAHT resulted from the GAHT rather than as a consequence of or risk factor for gender identity.231

Nguyen and colleagues232 published a recent review of cross-sectional and longitudinal studies from the last 5 years, nearly all from European cohorts, and summarized fewer depressive symptoms, anxiety, problems with socialization and interpersonal functioning, global functional impairment, interpersonal sensitivity and hostility in TW on GAHT compared with baseline. They also summarized the general findings above that GAHT is correlated with changes in global and regional brain volumes, white matter microstructure and in cognitive performance on sex-biased tasks requiring verbal and visual memory in the direction of gender identity rather than assigned sex.232 However, no studies have examined how GAHT influences executive function and cognitive domains used for daily living, and additional research will provide valuable data on these and other brain processes.

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moe_rikaApril 6, 2021, 8:39am#19

en.wikipedia.org

Causes of transsexuality | Brain structure

Several studies have found a correlation between gender identity and brain structure. A first-of-its-kind study by Zhou et al. (1995) found that in a region of the brain called the bed nucleus of the stria terminalis (BSTc), a region which is known for sex and anxiety responses (and which is affected by prenatal androgens), cadavers of six persons who were described as having been male-to-female transsexual or transgender persons in life had female-normal BSTc size, similar to the study’s c In a …

Brain structure

General

Several studies have found a correlation between gender identity and brain structure.[8] A first-of-its-kind study by Zhou et al. (1995) found that in a region of the brain called the bed nucleus of the stria terminalis (BSTc), a region which is known for sex and anxiety responses (and which is affected by prenatal androgens),[9] cadavers of six persons who were described as having been male-to-female transsexual or transgender persons in life had female-normal BSTc size, similar to the study’s cadavers of cisgender women. While those identified as transsexual had taken hormones, this was accounted for by including cadavers of non-transsexual male and female controls who, for a variety of medical reasons, had experienced hormone reversal. The controls still had sizes typical for their gender. No relationship to sexual orientation was found.[10]

In a follow-up study, Kruijver et al. (2000) looked at the number of neurons in BSTc instead of volumes. They found the same results as Zhou et al. (1995), but with even more dramatic differences. One MtF subject, who had never gone on hormones, was also included and matched up with the female neuron counts nonetheless.[11]

In 2002, a follow-up study by Chung et al. found that significant sexual dimorphism (variation between sexes) in BSTc did not become established until adulthood. Chung et al. theorized that either changes in fetal hormone levels produce changes in BSTc synaptic density, neuronal activity, or neurochemical content which later lead to size and neuron count changes in BSTc, or that the size of BSTc is affected by the generation of a gender identity inconsistent with one’s assigned sex.[12]

It has been suggested that the BSTc differences may be due to the effects of hormone replacement therapy. It has also been suggested that because pedophilic offenders have also been found to have a reduced BSTc, a feminine BSTc may be a marker for paraphilias rather than transsexuality.[2]

In a review of the evidence in 2006, Gooren considered the earlier research as supporting the concept of transsexuality as a sexual differentiation disorder of the sex dimorphic brain.[13] Dick Swaab (2004) concurs.[14]

In 2008, a new region with properties similar to that of BSTc in regards to transsexuality was found by Garcia-Falgueras and Swaab: the interstitial nucleus of the anterior hypothalamus (INAH3), part of the hypothalamic uncinate nucleus. The same method of controlling for hormone usage was used as in Zhou et al. (1995) and Kruijver et al. (2000). The differences were even more pronounced than with BSTc; control males averaged 1.9 times the volume and 2.3 times the neurons as control females, yet regardless of hormone exposure, MtF transsexuals were within the female range and the FtM transsexual within the male range.[15]

A 2009 MRI study by Luders et al. of 24 MtF transsexuals not yet treated with cross-sex hormones found that regional gray matter concentrations were more similar to those of cisgender men than to those of cisgender women, but there was a significantly larger volume of gray matter in the right putamen compared to cisgender men. Like earlier studies, it concluded that transsexuality was associated with a distinct cerebral pattern.[16] (MRI allows easier study of larger brain structures, but independent nuclei are not visible due to lack of contrast between different neurological tissue types, hence other studies on e.g. BSTc were done by dissecting brains post-mortem.)

An additional feature was studied comparing 18 female-to-male transsexuals who had not yet received cross-sex hormones with 24 cisgender male and 19 female gynephilic controls, using an MRI technique called diffusion tensor imaging or DTI.[17] DTI is a specialized technique for visualizing white matter of the brain, and white matter structure is one of the differences in neuroanatomy between men and women. The study took into account fractional anisotropy values for white matter in the medial and posterior parts of the right superior longitudinal fasciculus (SLF), the forceps minor, and the corticospinal tract. Rametti et al. (2010) discovered that, “Compared to control females, FtM showed higher FA values in posterior part of the right SLF, the forceps minor and corticospinal tract. Compared to control males, FtM showed only lower FA values in the corticospinal tract.”[17] The white matter pattern in female-to-male transsexuals was found to be shifted in the direction of biological males.

Hulshoff Pol et al. (2006) studied the gross brain volume of 8 male-to-female transsexuals and in six female-to-male transsexuals undergoing hormone treatment. They found that hormones changed the sizes of the hypothalamus in a gender consistent manner: treatment with male hormones shifted the hypothalamus towards the male direction in the same way as in male controls, and treatment with female hormones shifted the hypothalamus towards the female direction in the same way as female controls. They concluded: “The findings suggest that, throughout life, gonadal hormones remain essential for maintaining aspects of sex-specific differences in the human brain.”[18]

A 2016 review agreed with the other reviews when considering androphilic trans women and gynephilic trans men. It reported that hormone treatment may have large effects on the brain, and that cortical thickness, which is generally thicker in cisgender women’s brains than in cisgender men’s brains, may also be thicker in trans women’s brains, but is present in a different location to cisgender women’s brains.[2] It also stated that for both trans women and trans men, “cross-sex hormone treatment affects the gross morphology as well as the white matter microstructure of the brain. Changes are to be expected when hormones reach the brain in pharmacological doses. Consequently, one cannot take hormone-treated transsexual brain patterns as evidence of the transsexual brain phenotype because the treatment alters brain morphology and obscures the pre-treatment brain pattern.”[2]

Androphilic male-to-female transsexuals

Studies have shown that androphilic male-to-female transsexuals show a shift towards the female direction in brain anatomy. In 2009, a German team of radiologists led by Gizewski compared 12 androphilic transsexuals with 12 cisgender males and 12 cisgender females. Using functional magnetic resonance imaging (fMRI), they found that when shown erotica, the cisgender men responded in several brain regions that the cisgender women did not, and that the sample of androphilic transsexuals was shifted towards the female direction in brain responses.[19]

In another study, Rametti and colleagues used diffusion tensor imaging (DTI) to compare 18 androphilic male-to-female transsexuals with 19 gynephilic males and 19 androphilic cisgender females. The androphilic transsexuals differed from both control groups in multiple brain areas, including the superior longitudinal fasciculus, the right anterior cingulum, the right forceps minor, and the right corticospinal tract. The study authors concluded that androphilic transsexuals were halfway between the patterns exhibited by male and female controls.[20]

A 2016 review reported that early-onset androphilic transgender women have a brain structure similar to cisgender women’s and unlike cisgender men’s, but that they have their own brain phenotype.[2]

Gynephilic male-to-female transsexuals

Research on gynephilic trans women is considerably limited.[2] While MRI taken on gynephilic male-to-female transsexuals have likewise shown differences in the brain from non-transsexuals, no feminization of the brain’s structure have been identified.[2] Neuroscientists Ivanka Savic and Stefan Arver at the Karolinska Institute used MRI to compare 24 gynephilic male-to-female transsexuals with 24 cisgender male and 24 cisgender female controls. None of the study participants were on hormone treatment. The researchers found sex-typical differentiation between the MtF transsexuals and cisgender males, and the cisgender females; but the gynephilic transsexuals “displayed also singular features and differed from both control groups by having reduced thalamus and putamen volumes and elevated GM volumes in the right insular and inferior frontal cortex and an area covering the right angular gyrus”.[21]

The researchers concluded that:

Contrary to the primary hypothesis, no sex-atypical features with signs of ‘feminization’ were detected in the transsexual group … The present study does not support the dogma that [male-to-female transsexuals] have atypical sex dimorphism in the brain but confirms the previously reported sex differences. The observed differences between MtF-TR and controls raise the question as to whether gender dysphoria may be associated with changes in multiple structures and involve a network (rather than a single nodal area).[21]

Berglund et al. (2008) tested the response of gynephilic MtF transsexuals to two steroids hypothesized to be sex pheromones: the progestin-like 4,16-androstadien-3-one (AND) and the estrogen-like 1,3,5(10),16-tetraen-3-ol (EST). Despite the difference in sexual orientation, the MtFs’ hypothalamic networks activated in response to the AND pheromone, like the androphilic female control groups. Both groups experienced amygdala activation in response to EST. Gynephilic male control groups experienced hypothalamic activation in response to EST. However, the MtF subjects also experienced limited hypothalamic activation to EST. The researchers concluded that in terms of pheromone activation, MtFs occupy an intermediate position with predominantly female features.[22] The MtF transsexual subjects had not undergone any hormonal treatment at the time of the study, according to their own declaration beforehand, and confirmed by repeated tests of hormonal levels.[22]

A 2016 review reported that gynephilic trans women differ from both cisgender male and female controls in non-dimorphic brain areas.[2]

Gynephilic female-to-male transsexuals

Fewer studies have been performed on the brain structure of transgender men than on transgender women.[2] A team of neuroscientists, led by Nawata in Japan, used a technique called single-photon emission computed tomography (SPECT) to compare the regional cerebral blood flow (rCBF) of 11 gynephilic FtM transsexuals with that of 9 androphilic cis females. Although the study did not include a sample of biological males so that a conclusion of “male shift” could be made, the study did reveal that the gynephilic FtM transsexuals showed significant decrease in blood flow in the left anterior cingulate cortex and a significant increase in the right insula, two brain regions known to respond during sexual arousal.[23]

A 2016 review reported that the brain structure of early-onset gynephilic trans men generally corresponds to their assigned sex, but that they have their own phenotype with respect to cortical thickness, subcortical structures, and white matter microstructure, especially in the right hemisphere.[2] Morphological increments observed in the brains of trans men might be due to the anabolic effects of testosterone.[2]

Prenatal androgen exposure

Prenatal androgen exposure, the lack thereof, or poor sensitivity to prenatal androgens are commonly cited mechanisms to explain the above discoveries. To test this, studies have examined the differences between transsexual and cisgender individuals in digit ratio (a generally accepted marker for prenatal androgen exposure). A meta-analysis concluded that the effect sizes for this association were small or nonexistent.[24]

Congenital adrenal hyperplasia in persons with XX sex chromosomes results in what is considered to be excess exposure to prenatal androgens, resulting in masculinization of the genitalia and, typically, controversial prenatal hormone treatment[25] and postnatal surgical interventions.[26] Individuals with CAH are usually raised as girls and tend to have similar cognitive abilities to the typical female, including spatial ability, verbal ability, language lateralization, handedness and aggression. Research has shown that people with CAH and XX chromosomes will be more likely to be same sex attracted,[25] and at least 5.2% of these individuals develop serious gender dysphoria.[27]

In males with 5-alpha-reductase deficiency, conversion of testosterone to dihydrotestosterone is disrupted, decreasing the masculinization of genitalia. Individuals with this condition are typically raised as females due to their feminine appearance at a young age. However, more than half of males with this condition raised as females become males later in their life. Scientists speculate that the definition of masculine characteristics during puberty and the increased social status afforded to men are two possible motivations for a female-to-male transition.[27]

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namenomonster (苏暖暖)April 6, 2021, 8:46am#20

虽然不知道删除了什么,但是我得说
不要拿删除当隐藏用,删除就等于是不希望我看到哦
所以我不会点进去一个一个看的

1 Like

moe_rikaApril 6, 2021, 8:50am#21

Contrary to the primary hypothesis, no sex-atypical features with signs of ‘feminization’ were detected in the transsexual group … The present study does not support the dogma that [male-to-female transsexuals] have atypical sex dimorphism in the brain but confirms the previously reported sex differences. The observed differences between MtF-TR and controls raise the question as to whether gender dysphoria may be associated with changes in multiple structures and involve a network (rather than a single nodal area).

与最初的假设相反,在跨性别群体…中没有检测到有女性化迹象的性别非典型特征 。目前的研究并不支持[男性到跨性别女性]在大脑中存在非典型的性二态性的学说,但证实了之前报道的性别差异。观察到的MTF-TR和对照组之间的差异提出了一个问题,即性别焦虑是否可能与多个结构的变化有关,并涉及一个网络(而不是一个单一的结节区域)。

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namenomonster (苏暖暖)April 6, 2021, 8:51am#22

也就是说会有影响,但是并非简单的分界线,而是某种复杂模式的形成

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那么,跨性别者的大脑…… - 脱水菜 - limelight.pdf (561.2 KB)

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