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"How do you scientifically detect a "masculinized brain"?"

There has been progress in the area of positron emission tomography. There are detectable differences in patterns of brain activity.

The other method can only be done at autopsy. The process is to take cross sections if critical structures, such as the hypothalamus and do staining to reveal structural differences.

One word of caution about interpreting research findings of this nature: A large number of individuals must be examined, because the research goal is to compare the mean size for the area in question. Comparing the mean is a much better test for detecting differences. A large sample size gives improved resolution to such tests. It is exactly the same methodology used in process control in engineering disciplines.

Some of the research results that are significant.

1. The findings of Swaab, et al, indicated the mean size of the BSTc region of transgender individuals (MTF) is more consistent with that of women than men. The results for the comparison against the mean for males is significant at the P less than 0.005 level. Again, it is the comparison of the means.

2. Studies on sheep are also revealing. There is a percentage of rams that exhibit 'homosexual behavior', preferring sex with other rams, over that with ewes. Dissection of their brains revealed differences in the pre-optic region of the brain. Again, the comparison is on the mean size of the region.

3. Finally, PET scans revealed that male gays had their hypothalamus show increased activity in response to male pheromones (that were metabolic products of testosterone) instead of the pheromones derived from estrogen. It would seem that this difference is due to biological differences, because it is doubtful the hypothalamus is subject to conscious control.