Few emotions are more discussed, sung about, and central to a story than love and sex. They give rise to intense emotions, and scientists have asked for years which part of the brain they involve.

Most people can relate to having asked themselves whether they are in love or in lust with a person. Turns out, the two emotions stimulate different but related structures in the brain.

Researchers pooled brain imaging data from 20 studies and mapped the zones that lit up as people viewed erotic images or pictures of their romantic partners. What emerged were two structures called the insula and striatum. Both facilitate the feelings behind sex and love, and provide evidence that first comes lust before love can follow. When a person feels desire it is the insula that brings it to consciousness.

Located in the cerebral cortex, the insula connects the limbic system, which is a primitive emotion area, to the cortex, where higher thinking occurs. This way we become aware of our feelings and attribute meaning to them.

Brain images also reveal that the back portion of the insula is triggered by desire, the front by romantic feelings, and the middle portion by someone you love and desire. As this is happening, the striatum is also triggered. Located close to the insula, the striatum coordinates planning and executing pathways so that when a person is motivated, they act – for example, on the object of their love and desire.

The striatum also has reward pathways activated by sex and food, allowing a person to feel pleasure by these stimuli. Over time, as sexual pleasure with someone continues, the striatum's other function of conditioning rewards the action and paves the way for sexual desire to progress to love.

Drug addictions trigger the same pathways, proving what people have always felt ' that love is addictive.