"Understanding the structure gives you a sense of function," says Professor Michael Sneary.
Sneary is referring to the brain scans of a straight male and female and a gay man and a lesbian.
Colored areas in his diagrams show that straight male's brains are similar to those in the lesbian's and gay male's brain activity is similar to that of a straight woman's brain.
The scans were provided by the Karolinska Institute where this research was conducted with 90 subjects.
Doctor Michael Sneary is a neurobiologist at San Jose State University.
"They're shaped like each other and if the structure of the two sides are structurally similar in homosexuals and in women, it's a reflection that they function in the same way," says Sneary.
The Swedish researcher, Ivnaka Savic, says she and her colleagues chose to measure areas of the brain likely to have been fixed at birth.
"This is the most robust measure so far of cerebral differences between homosexual and heterosexual subjects," says Ivnaka Savic.
They say the scans reveal that in gay people, key structures of the brain governing emotion, mood, anxiety and aggressiveness resemble those of straight people of the opposite sex.
"That was the whole point of the study, to show the parameters that differ, but which couldn't be altered by learning or cognitive processes," says Savic.
The study finds hetero and homosexuality is fixed at birth.
"I think this is just more evidence that the behaviors are linked to things that are hardwired at birth," says Sneary.
Sneary finds the study beneficial for medical science. He says understanding the structure of the brain improves our understanding of its function, which could lead to new therapeutic treatments.
The Swedish researchers do acknowledge that these differences in the brain could be inherited or result from abnormally high or low exposure to sex hormones such as testosterone.