Researchers quizzed 180 young men and women about their attitude towards relationships and tested them for a gene called DRD4, which affects levels of the brain chemical dopamine.

Dopamine is thought to be the "pleasure chemical, " producing a feeling of bliss. Norepinephrine is similar to adrenaline and produces the racing heart and excitement.

There were differences -- long-term romantic love lit up many more brain regions than early-stage love -- but both groups showed significant activity in the dopamine-rich ventral tegmental area.