Neuro-biology of trans-sexuality : Prof. Robert Sapolsky

Summary

The script delves into the neurobiology of sexual orientation and gender identity, highlighting the lesser-studied aspects in women such as the fourth to second finger ratio and auto acoustic reflex. It emphasizes the historical misclassification of homosexuality and transsexuality as psychiatric disorders, with a landmark study suggesting transsexuality is about having the 'wrong' gendered body. The discussion also touches on the intriguing absence of phantom limb syndrome in transgender individuals post-surgery, opening up new research avenues in neurobiology and gender identity.

Takeaways

• 📊 The neurobiology of sexual orientation in women is understudied compared to men, with only a few studies available.
• 👐 The fourth to second finger ratio in gay women tends to be more similar to that of straight men, suggesting a biological link.
• 🔊 The auto acoustic reflex has been shown to differ between gay and straight individuals, indicating a neurobiological distinction.
• 🏥 Historically, homosexuality was considered a psychiatric disorder until the 1970s when the APA removed it from the DSM.
• 🧠 The neurobiology of transsexuality has been studied less extensively, but research suggests a difference in the size of the bed nucleus of the striae terminalis in transsexual individuals.
• 🧬 The size of the brain region mentioned is not influenced by hormones but rather by the individual's self-identified gender, as shown in both pre- and post-transition stages.
• 🏥 Postmortem studies of transsexual brains have shown that the size of the brain region aligns with the gender the individual identifies with, not their biological sex.
• 💉 Hormonal treatments for conditions like testicular cancer do not affect the size of the brain region in question, indicating the difference is not due to hormone therapy.
• 🏙️ The study's findings have implications for societal understanding and policies, such as medical insurance coverage for transgender operations in San Francisco.
• 🤔 The study raises questions about the nature of gender identity and suggests that transsexuality may be more about having the 'wrong' gendered body than a psychological issue.
• 🔬 A study on phantom limb syndrome in transgender individuals who have had their penises removed shows a lack of penile phantom sensation, suggesting a unique neurobiological response.

Q & A

What is the fourth to second finger ratio, and how does it relate to sexual orientation in women?

The fourth to second finger ratio, often referred to as the 2D:4D ratio, is a measure that has been found to be different in gay women compared to straight women. On average, gay women have a ratio more typical of straight men, suggesting a possible biological marker for sexual orientation.

What is the auto acoustic reflex, and how is it related to sexual orientation?

The auto acoustic reflex is a phenomenon that has been studied in the context of sexual orientation. While the script does not provide specific details about this reflex, it suggests that it is another biological indicator that has been observed to differ between gay and straight individuals.

How has the perception of transsexuality evolved in the psychiatric field?

Transsexuality was once considered a psychiatric disorder, similar to homosexuality which was classified as such until the early 1970s. However, a landmark decision by the American Psychiatric Association reclassified homosexuality as not a psychiatric disorder, and the perception of transsexuality has also shifted, moving away from being purely a domain of psychopathology.

What is the bed nucleus of the striae terminalis, and what does it reveal about the neurobiology of transsexuality?

The bed nucleus of the striae terminalis is a region of the brain that shows sex differences in its average size. Studies have shown that in the brains of transsexual individuals, this region is the size of the sex they identify with, not the sex they were born with, suggesting a biological basis for their gender identity.

How did researchers control for the effects of hormone treatments in their study of the bed nucleus of the striae terminalis in transsexuals?

Researchers controlled for the effects of hormone treatments by including both transsexuals who had undergone gender changes and those who had not. They also compared these results with men treated with feminizing hormones for testicular cancer, finding no similar changes in the brain region, indicating that the observed differences were not due to hormone treatments.

What is the significance of the study on the bed nucleus of the striae terminalis in transsexuals?

The study is significant because it suggests that transsexuality is not about people who think they are a different gender but rather about people who have the 'wrong gendered body.' This finding challenges previous perceptions and supports the idea that gender identity is deeply rooted in brain structure.

What is phantom limb syndrome, and how does it relate to the study of transsexualism?

Phantom limb syndrome is a phenomenon where individuals who have lost a limb continue to feel sensations as if the limb were still there. In the context of transsexualism, the absence of penile phantom sensation in individuals who have undergone gender reassignment surgery suggests a deeper congruence between their physical body and their gender identity.

What was the study conducted by Dutch scientists regarding the brain region and transsexualism?

The Dutch scientists conducted a study focusing on the bed nucleus of the striae terminalis in transsexual individuals. They found that the size of this brain region corresponded to the gender these individuals identified with, rather than their biological sex, supporting the notion that transsexualism involves a mismatch between body and gender identity.

How did the city of San Francisco's decision on medical insurance for transgender operations coincide with the publication of the study?

The study's publication around the same time as San Francisco's decision to cover transgender operations in city employees' medical insurance is coincidental. There is no evidence to suggest that the study directly influenced the city's policy, but it highlights the broader implications and interest in the neurobiology of gender identity.

What are the implications of the neurobiological findings on sexual orientation and transsexuality for the understanding of gender identity?

The neurobiological findings suggest that gender identity is not solely a social construct but has a biological basis. This understanding can help in the development of more empathetic and informed approaches to the treatment and recognition of diverse gender identities.

What role do sensory triggers play in the neural mechanisms of sexual behavior?

Sensory triggers are believed to activate neural mechanisms that influence sexual behavior. The script suggests that the environment can release these fixed action patterns through sensory inputs, although it does not specify the exact nature of these triggers.