of hormonal levels. Gynephilic trans men Fewer brain structure studies have been performed on transgender men than on transgender women. 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 trans men with that of 9 androphilic cis females. Although the study did not include a sample of cisgender males so that a conclusion of "male shift" could be made, the study did reveal that the gynephilic trans men 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. 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. Morphological increments observed in the brains of trans men might be due to the anabolic effects of testosterone. Prenatal androgen exposure Prenatal androgen exposure, the lack thereof, or low sensitivity to prenatal androgens are commonly cited as mechanisms to explain the above discoveries. To test this, studies have examined the differences between trans 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. In people with XX chromosomes, congenital adrenal hyperplasia (CAH) results in heightened exposure to prenatal androgens, resulting in masculinization of the genitalia. Individuals with CAH are typically subjected to medical interventions including prenatal hormone treatment and postnatal genital reconstructive surgeries. Such treatments are sometimes criticized by intersex rights organizations as non-consensual, invasive, and unnecessary interventions. Individuals with CAH are usually assigned female and tend to develop similar cognitive abilities to the typical females, 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 experience same-sex attraction, and at least 5.2% of these individuals develop serious gender dysphoria. 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 assigned female and raised as girls due to their feminine appearance at a young age. However, more than half of males with this condition raised