Biology and sexual orientation INAH3 weight for the heterosexual male brains was significantly larger than for the heterosexual female brains, while the results for the gay male group were between those of the other two groups but not quite significantly different from either. The neuron count also found a male-female difference in INAH3, but found no trend related to sexual orientation. A 2010 study, Garcia-Falgueras and Swaab asserted that "the fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge.
Sexual arousal role in determining how a person will respond in any given sexual situation. On the other hand, a person may be hypersexual, which is a desire to engage in sexual activities considered abnormally high in relation to normal development or culture, or suffering from a persistent genital arousal disorder, which is a spontaneous, persistent, and uncontrollable arousal, and the physiological changes associated with arousal. Sexual arousal causes various physical responses, most significantly in the sex organs (genital organs). Sexual arousal for a man is usually indicated by the swelling and erection of the penis when blood fills the corpus cavernosum.