“Love is blind” says the well known adage and now it officially also renders you stupid, according to new research. Prof Robin Dunbar, an evolutionary psychologist, argues that the rational parts of the human brain shut down when experiencing the feelings of love. Dunbar developed his theory after analysing the findings of UK brain experiments. The MRI research looked at the brain activity of 17 volunteers as they were shown pictures of their boyfriends and girlfriends, with whom they were “truly, madly and deeply in love.” Dunbar says that when the people gazed at images of their loved ones, the rational parts of their brain were affected by “rose-tinted spectacle syndrome” and their hearts ruled their heads, dulling their critical faculties. “What seems to be happening is that you have subconsciously made up your mind that you are interested in the person and the rational bit of the brain — the bit that would normally say ‘hang on a minute’ — gets switched off,” Dunbar explained. “In a relationship you are in a trade-off between caution and just going for it. But if you don’t engage, you won’t form relationships. If the prefrontal cortex is shut down, that protective and cautious element goes.”