There are different parts of the brain that are considered to be responsible for sexual orientation. For example, the limbic system is in charge of making sure that people experience pleasure especially when they are experiencing sex.
The hypothalamus, amygdala, and the hippocampus are known to have some effects on the sexuality that people may experience. There are still a lot of scientists who are trying to learn more about sexuality in general. They usually look at the sexual activities that people choose to engage in. They may even check what parts of the brain usually react depending on the attraction that a person feels toward someone.