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Sammy, MSc Profile picture
@NeuroSGS
May 29 • 3 tweets • 2 min read Twitter logo Read on Twitter
The fraternal birth order effect (FBOE) is the finding that gay men, on average, have a greater number of older brothers (and the more older brothers increases the likelihood of homosexuality in the youngest offspring). The maternal immune hypothesis posits that an immune… twitter.com/i/web/status/1… Image
NLGN4Y is a male-specific cell adhesion molecule that is expressed in the fetal brain and is located at the post-synaptic membrane (thus accessible to circulating antibodies).

With more male pregnancies, women generate successively more anti-NLGN4Y antibodies: Image
Here is a schematic of the hypothesised effect: Image

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More from @NeuroSGS

Sammy, MSc Profile picture
May 27
Large study investigating sex differences in gray matter volume (GMV) in a large sample (n=2,838) of men and women between the ages of 21-90 years old: Image
Women, on average, showed larger GMV in various frontal regions, such as the ventrolateral and dorsolateral prefrontal cortex, medial and lateral orbitofrontal cortex, and anterior cingulate cortex. Image
Males instead showed larger GMV, on average, in sub-cortical regions such as the parahippocampal gyrus and hippocampus, amygdala, temporal pole, putamen, fusiform gyrus, anterior cerebellar hemisphere, primary visual cortex, and premotor cortex.
Read 6 tweets
Sammy, MSc Profile picture
May 4
Important data to consider when investigating the sociological and biological elements of female-typical gendered behaviour:
researchgate.net/publication/24…
Notice how females exposed to the lowest levels of testosterone in utero (top line) show more and more “female-typical” behaviour in adulthood with more and more encouraged femininity from their mothers (sociological effects of increasing certain behaviours) Image
Also notice how girls exposed to slightly higher prenatal testosterone (middle lines) show less “female-typical” behaviour despite the same levels of femininity encouraged by parents.
Read 5 tweets
Sammy, MSc Profile picture
Apr 14
This article is often cited as evidence that the brains of transgender women (TW) resemble the brains of natal women. However, once looking at the data, we see that this may not be the case.
ncbi.nlm.nih.gov/pmc/articles/P…
The study included 48 controls (24=male; 24=female) and 24 TW (mean age = 45 for all participants).

All subjects underwent MRI and then the authors implemented a multivariate classifier to these MR images, in which a brain sex index (BSI) was derived. The BSI ranges between “0”… twitter.com/i/web/status/1…
The classifier achieved 88.3% accuracy when assessing the 48 natal male and female control brains.

The BSI of TW was estimated as 0.75 ± 0.39, which was shifted by 25% towards female (still being MUCH closer to males; see figure 1 below): Image
Read 7 tweets
Sammy, MSc Profile picture
Dec 3, 2022
So, here is my response to @ForrestValkai and his video "Sex and Sensibility", breaking down his segment on transgender neurology.
He mentions 3 main sub-cortical structures:

1) The central division of the bed nucleus of the stria terminalis (BSTc)

2) The sexually dimorphic nucleus of the preoptic area (SDN-POA)

3) The vasoactive intestinal polypeptide subdivision of the suprachiasmatic nucleus (VIP-SCN).
Starting with the BSTc, it's been reported that this nucleus is sexually dimorphic (i.e., the BSTc is significantly larger and the number of somatostatin neurons is 71% greater in males compared to females):
pubmed.ncbi.nlm.nih.gov/10843193/#:~:t….
Read 24 tweets
Sammy, MSc Profile picture
Nov 27, 2022
Are there differences in certain white matter fiber tracts in the brains of female-to-male transsexuals (FtMs) either pre- or post-androgen treatment?

Let's take a look 👀
The authors of this study implemented diffusion tensor imaging (DTI) to measure fractional anisotropy (FA) in FtMs and male and female controls.

A high FA = high white matter integrity
A low FA = low white matter integrity

pubmed.ncbi.nlm.nih.gov/20562024/
All 18 untreated FtMs were defined as the "early on-set" type (pre-puberty), all were homosexual (important later on), and all had hormone levels within the typical female range:
Read 13 tweets
Sammy, MSc Profile picture
Nov 25, 2022
Here is a study investigating sex-atypical hypothalamic responses/activation to androstadienone (AND) in pre-pubertal children and adolescents with gender dysphoria (GD) compared with neurotypical male and female controls.

Let's take a look 👀
pubmed.ncbi.nlm.nih.gov/24904525/
Quick background:

AND is a precursor in the biosynthesis of both testosterone and estrogen (see below), in which its production is increased throughout male puberty and acts as a pheromone in human sweat. Image
There is a known sex difference in the olfactory threshold to AND, where males become desensitized (i.e., have an increased threshold to elicit a response) whereas females become sensitized (i.e., have a lower threshold to elicit a response).
pubmed.ncbi.nlm.nih.gov/15708759/
Read 19 tweets

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