More recently, scientists have started to focus on measuring changes in brain activity related to sexual arousal, by using brain-scanning techniques. A study on how heterosexual and homosexual men's brains react to seeing pictures of naked men and women has found that both hetero- and homosexual men react positively to seeing their preferred sex, using the same brain regions. The only significant group difference between these orientations was found in the amygdala, a brain region known to be involved in regulating fear.