More specifically, a protein in semen penetrates women’s brains, passing the blood brain barrier into the hypothalamus and pituitary gland and causing the release of the hormones required for pregnancy. Apparently, semen can cause women to ovulate.
Researchers have found that this protein exists in animals all over the world. Although women are spontaneous ovulators, meaning that they ovulate whether they are sexually active or not, Chinese researchers hypothesized in 1985 that there may be a mechanism for inducing ovulation in human females other than a monthly cycle. Because the idea was so counter-intuitive to common knowledge at the time, scientists simply ignored it!
In 2005, researchers decided to test the Chinese theory once and for all. Strangely, it turned out to be accurate. Some animals, like rabbits and camels, ovulate in response to sexual activity. They are known as induced ovulators. To test the theory, researchers
injected the seminal fluid of male llamas—closely related to camels—into the hind legs of female llamas to see if the llamas would ovulate without genital stimulation. To their surprise, he says, injecting seminal fluid into the female llamas’ bloodstream had ‘a very potent ovulatory effect.’
This spurred the researchers to find what it was that was causing the ovulatory effect. It turned out to be a well known protein known as neural growth factor, or NGF, which is essential to the development and survival of sensory neurons. It is also widely present in most animals. The most surprising part is that the effects of the protein can be seen across species; NGF found in bull semen causes the release of ovulatory chemicals in human females. Additionally, the research confirmed what is stated above; NGF travels into the brain to work its ovulation magic.
The researchers believe this could lead to new types of therapy for couples that are having fertility trouble and are unable to conceive.
That is at least the second male substance that researchers have found within the female brain. They also recently found that women who give birth to boys have male DNA in their brains for the rest of their lives.