Stria Terminalis - Bed Nucleus of The Stria Terminalis

Bed Nucleus of The Stria Terminalis

The central subdivision of the bed nucleus of the stria terminalis (BSTc) is sexually dimorphic. On average, the BSTc is twice as large in men as in women and contains twice the number of somatostatin neurons. A sample of six male-to-female transsexuals taking estrogen were found to have female-typical number of cells in the BSTc, whereas a female-to-male transsexual taking testosterone was found to have a male-typical number. The authors (W. Chung, G. De Vries, Dick Swaab) also examined subjects with hormone-related disorders and found no pattern between those disorders and the BSTc while the single untreated male-to-female transsexual had a female-typical number of cells. They concluded that the BSTc provides evidence for a neurobiological basis of gender identity disorder and proposed that such was determined before birth.

Criticisms of the former statement suggest the study used an unrepresentative sample and did not adequately control for hormone replacement therapy, which has been shown to influence hypothalamic size, even though the study tried to do this by including non-transsexual male and female controls which, for a variety of medical reasons, had experienced hormone reversal. The statement about the neurobiological basis from birth has later been brought to question, though not refuted, by a follow up study by the same group which found that the sexual dimorphism of the BSTc is not present before adulthood (approximately 22 years of age) even though transsexuals report being aware of their gender identity since childhood.

Reduction of the size of the bed nucleus of the stria terminalis has been observed in pedophilic male perpetrators, in addition to reductions in the right amygdala, hypothalamus and abnormalities in related structures. The authors propose that childhood deficits in the BNST and medial amygdala may cause inhibition of sexual maturity.