In English the colour green is associated with jealousy, which is sometimes jokingly called 'the green-eyed monster'. But it's no joke when jealousy takes over your life. Researchers are only starting to understand how jealousy can go wrong in the human brain.

Mild jealousy is a normal, healthy emotion; it's part of what makes us tick. Who hasn't experienced sibling rivalry or felt left out when their partner spends time with other people? Feeling jealous helps us value our loved ones and protect our important relationships.

But for a small number of us, extreme jealousy can lead to obsessive behaviour like stalking. It can also cause depression, destroy relationships and even kill – morbidly jealous people can become violent or suicidal.

Now researchers in Italy believe they've found the area of the brain responsible for obsessive jealousy, which is called Othello's syndrome, named after the Shakespeare character who kills his wife because of jealousy.

The ventromedial prefrontal cortex is just above the forehead. This is the part of the brain which processes emotions, including thinking about those we love. But crucially, we use this part of the brain to predict scenarios of losing our loved ones, and thinking about how we would feel if that happened.

Obsessively jealous people spend too much time dwelling on these scenarios. For them, losing their relationship starts to seem like the end of the world. Worryingly, the researchers believe that, in some people, this process may become a habit, and jealousy becomes hardwired in the brain.

They want to investigate medicines which could help treat people suffering from this devastating condition.