Brain volume, activation patterns

Last month, it became clear to us that volume of the right putamen cannot conclude with certainty that gender identity has biological basis. This week, we will proceed to other grey matter studies in our search for the proof that indeed gender identity, like sex identity, has biological basis as what Saraswat, Weinand and Safer tried to claim in their 2015 report in the journal Endocrine Practice.

The report cited four studies of three research teams supposedly showing evidence that differences in the volume and activation patterns of the brain differentiates gender identity.

A 2011 study by Savic and colleagues observed significant brain volume reductions in 24 male-to-female (MTF) transgenders (living) compared to controls (male and female). This finding, however, contradicts with the right putamen findings we discussed last month. In that study, the right putamen increased in volume among MTF samples (dead). The biological question is, is it logical to say that in MTF transgenders the right putamen increases in volume while the brain shrinks? Interestingly, Saraswat, Weinand and Safer did not raise a question in this incongruence but rationalized that the Savic findings nevertheless showed a difference.

The right putamen researchers also noted that, when allowed to smell steroidal compounds (an estrogen derivative and a progesterone-like compound), the MTF subjects showed activated hypothalamus in a “sex-differentiated” manner. The MTF subjects who were not given the two steroidal compounds responded much like the female controls. It is however not indicated if the study used male controls. Although, Saraswat, Weinand and Safer interpreted it as proof for sex differentiation based on gender identity, it instead appears to prove that the external steroidal intervention caused the differentiation.

Moreover, the similarity in the responses of the MTF subjects and the female controls cannot be validly concluded as proof of the MTF gender being similar to the female gender for two obvious grounds. First, by principle, the female gender should be different from the MTF gender outside differences or similarities (after surgery) of sexual equipment. Second, in the absence of male controls, there is no way of verifying if male controls too respond similarly with the female controls, which invalidates the assumed “sex-differentiated” conclusion.

Honestly, the more I delve into the proof that Saraswat, Weinand and Safer presented to support the contention that gender identity is biologically based, the more I realized that there is no proof so far that is conclusive. Moreover, my impression also grew that the authors seemed to push the “proof” as empirically founded even if objective evaluation shows otherwise.