Natalie Portman believes studying psychology at university helped her understand her character in 'Black Swan'.

The 29-year-old actress - who plays ballet dancer Nina Sayers in the Darren Aronofsky-directed thriller movie - thinks studying at Harvard directly translated to her experience on the film because she could understand her obsessive compulsive tendencies and The Feeling of ritual involved in the dance.

She said: "This was actually a case where something I learned in school did translate into something practical in life, which is very, very rare. It was absolutely a case of obsessive compulsive behaviour. The scratching and the anorexia and bulimia are forms of OCD.

"Ballet really lends itself to that because there's such a sense of ritual, with wrapping the shoes every day and preparing new shoes for every performance. It's such a process. It's almost religious, in nature."

Despite having to undergo an intense health and fitness regime to get herself in the right shape for the role she quickly let go one the shoot was over.

She told "My first meal was pasta, for breakfast, lunch and dinner. I ate it all the time."