A new study has found similarities between the brains of homosexual people and those of straight people of the opposite sex. The investigation by the Stockholm Brain Institute in Sweden has yielded important results in understanding why some men and women are attracted to the same sex rather than the opposite one.

The research involved accurate magnetic resonance imagery (MRI) scans and positron emission tomography (PET) scans, both focusing on the amygdalae. They are almond-shaped groups of neurons located deep within the medial temporal lobes of the brain, which is somewhere around the middle of the brain.

The amygdalae are known to be connected to the hypothalamus and are involved in the sense of smell and pheromone-processing. They are also responsible for at least some of the formation and storage of memories associated with emotional events. Thus they control arousal and hormonal secretions.

It appears that the brain hemispheres tend to be symmetrical in gay men and straight women, while the right-hand brain hemisphere is enlarged in straight men and lesbians. The right hemisphere is responsible for holistic reasoning on many levels, including language. It is known that the head circumference of men, on average, is 2 percent larger than women's, while the men's brain weighs 11-12 percent more.

The similarities were also noted at the level of the amygdalae, which were similarly connected. The research, published in the Proceedings of the US National Academy of Sciences, sheds new light in understanding homosexuality.