Using a brain imaging technique, Swedish researchers have shown that when homosexual and heterosexual males are presented with two odors that may be involved in sexual arousal their brains tend to respond differently, and that the homosexual men tend to respond in the same way as heterosexual women, though it could not be determined whether this was cause or effect. The study was expanded to include homosexual women; the results were consistent with previous findings meaning that homosexual women were not as responsive to male identified odors, while their response to female cues was similar to that of heterosexual males. According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation.