Lang geleden dat ik hier was
, heel veel onderzoek gedaan in die tijd.
Hier iemand die alles naar mijn idee goed uiteen zet op een wat technischere manier. Enige kennis van Engels en Neurologie is vereist.
''In the womb, in a normal fetus, gonadal hormones (estrogen/testosterone) are sent to the brain and the body, depending on whether the child has XX or XY chromosomes. However, there are rare exceptions to this. When there are issues in sending hormones to the child's brain, it is believed to cause transgenderism''
I don't think this is an established theory. This is one guess, but it doesn't hold much water. This is essentially a description of how Androgen Insensitivity Syndrome (AIS) works. The thing about this particular mechanism is that it generally results in genital deformities at the least, and typically results in a very female phenotypic development. It also doesn't really help to explain female-to-male transgender development at all in theory, because the process that is being disrupted is the de-feminization of cell progeny. While this is a favorite theory online, it really doesn't hold up to scrutiny. Its more "well this is how AIS works, so MAYBE its true for trans brain development". A more plausible theory has less to do with some inherent issue of the embryo/fetus, but instead exogenous hormonal influence from the mother - e.g., if the mother is taking medications, or etc. that have an influence on their endogenous hormone levels - more androgens, or higher estrogen than is normal, that could potentially have an effect on their gender identity, or other development. While this is a more palatable theory, it also does not have much backing. It also makes you question how, if a male developed more feminine attributes due to a high-estrogen or low-androgen environmental hormones in utero, how is it that otherwise extremely masculine men identify as women? Under this model, your expectation that a gender identity would correspond with some other feminine attributes - low testosterone (not consistent with such aggressive behavior, or this person's size), higher pitched vocals, less than average height and muscular development, etc.
Their brains also react the same way to exposure to a hormone called androstadienone.
Sure. I assume you're referencing studies such as this one, which shows that sex a-typical pheremone responses are found in gender dysphoric children. Sure, that sounds convincing. Right until you realize that this is not a sex-based response, but a sexuality based response. Homosexual men exhibit the same response. Considering between 60 and 90% of gender dysphoric children end up desisting (I'll go ahead and note right now that trans-activists are doing their best to discredit these figures, but they use junk science to do so, which is easily demonstrated), and most of the desisters end up identifying as gay or bisexual, the results of the gender dysphoric children aren't all that surprising.
It is simply what developed in the womb that unfortunately has no cure other than to physically transition.
Even this claim is shady at best. Firstly, transitioning isn't a cure. It is a treatment for gender dysphoria. Secondly, as a treatment for GD, the science is still out on that one. In 2016, under the Obama administration, there was a petition to have SRS covered for trans people under Obamacare, as it was touted as the best treatment for dysphoria. The findings of the administration, after a review of the literature (which has been replicated other times as well, by other organizations) is that the scientific data does not actually support this position, and so that is why SRS doesn't have mandatory coverage under Obamacare. The idea that it is the best treatment has been touted by WPATH, and accepted by many other organizations - but this is politics, not science at this point. The science doesn't really confirm this treatment as effective as is advertised.
Now, onto the nitty-gritty.
As pointed out, there isn't a male brain and a female brain, so this is an absurd claim to begin with. But, as you've mentioned, there are sexually dimorphic regions for which statistically there are differences between sexes. But it is absolutely a stretch to suggest that these regions in trans people are "of the opposite sex".
In regard to white matter, (
https://www.nature.com/articles/s41598-017-17352-8) for instance in measuring mean fractional anisotropy (FA) of the Left and Right Cortico-Spinal tract, the mean FA is highest in Heterosexual males, slightly lower in homosexual males, slightly lower still in MtF transsexuals (but very similar to homosexuals), slightly lower still in FtM transsexuals, slightly lower (but very similar) in homosexual women, and lowest in heterosexual women.
The mean FA for MtF is still higher than FtM, and all the mean FA of all biological males is higher than the mean FA of all biological women. So while it is clear there is a difference in transsexuals, the difference is similar to that of homosexuals, and differs only in magnitude.
The paper plots these differences on a graph:
https://imgur.com/a/3z1HqAn
Gray matter provides the strongest evidence for a biological origin for a gender identity.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3877116/
Our findings support the notion that structural differences exist between subjects with GID and controls from the same biological gender. We found that transsexual subjects did not differ significantly from controls sharing their gender identity but were different from those sharing their biological gender in their regional GM volume of several brain areas, including ... Additionaly, we also found areas in the cerebellum and in the left angular gyrus and left inferior parietal lobule that showed significant structural difference between transgender subjects and controls, independent from their biological gender.
This study notes:
The regions found affected in our study are mainly involved in neural networks playing role in body perception, including memory retrieval, self-awareness, visual processing, body and face recognition and sensorimotor functions
So one interpretation of this data might be that gender identity disorders are a disorder of body perception and self-awareness. A paper supporting this hypothesis:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5738422/
It should also be noted that nearly every study out there mentions, at least in a footnote, that for any and all reported brain differences, the causal chain is unclear: that is to say, they have not yet determined if there difference in i.e. gray matter is resultant of being transsexual, or if being transsexual is resultant of gray matter. Our brains are fairly plastic, and its entirely possible (and probable in some cases) that the brain has changed its structure due to social impact of their condition, or etc. For instance, in the white matter citation above, it talks about the inferior front-occipital fasciculus (IFOF), which is actually an outlier in the analysis I provided above. In the IFOF, there is actually a marked difference in transsexuals, specifically, MtF transsexuals have an extremely low mean FA compared to all other subjects. This is also implicated in schizophrenia, depression, autism, etc, and its entirely possible the structure here is a result of those conditions (though it has been proposed in schizophrenia for detection of early-onset schizophrenia - so it may not be resulting of the condition). As the paper puts it:
Consequently, aberrant FA in the IFOF of transgender individuals may be underlying to the unconformity between their perception of self and their body. Importantly, this finding of sex-atypical FA values in the IFOF did not change after accounting for the more heterogeneous sexual orientation among the transgender participants.
One major region that is often referenced by trans activists is the BSTc. This region is sexually dimorphic, where in women it is smaller with higher neuronal density. But, you cannot use the BSTc to try to identify trans brains in anyone below the age of about 25, as this region seems to differentiate during a second puberty. So using this in children/adolescents as a possible test to accompany a GD diagnosis just doesn't work. So especially if you want to talk about treating gender dysphoria in children - at that stage in the game there is no difference between a male and female brain.
Beyond that, there are other brain regions which are sexually dimorphic that are 100% in line with the biological sex, and not the gender identity. For instance, the substantia nigra. There is new emerging evidence, leading to an entirely new field that shows that sex differences come from divergent origins, namely there are some sexually dimorphic traits that are genotypically derived, instead of derived from the gonadal phenotype, and its subsequent hormone regulation. One study (
http://www.cell.com/current-biology/ful ... 06)00066-2) has shown that the role of the SRY gene goes beyond gonadal phenotype differentiation, and has a direct developmental impact on the Substantia Nigra. This is a region of the brain is important for motor planning, reward-seeking, learning, and addiction - many behavior patterns where men and women are known to be sexually dimorphic. The difference seems to be that the SRY causes more tyrosine hydroxalase positive neurons to develop. This makes this portion of the brain more receptive to dopamine, which is a key player in male-behavior, as opposed to serotonin being a similar player in female-behavior.
While there are some typical differences in men and women, trans people are not as consistent as you suggest with being similar to their identified sex.