Context: 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.

Question: What have scientists started spending the most time on?
Answer: measuring changes in brain activity related to sexual arousal

Question: How do scientiest measure brain activity?
Answer: by using brain-scanning techniques

Question: How did both gay and straight men react to pictures of both naked men and women?
Answer: positively

Question: What was the only difference in the study between gay and straight men?
Answer: The only significant group difference between these orientations was found in the amygdala,

Question: What does the amygdala region of the brain do?
Answer: known to be involved in regulating fear.