What makes up a person? Are we just a sum of our memories? What is left if you take away our memories?

These were the questions preoccupying writer SJ Watson, as he wrote his debut novel, Before I Go To Sleep (Black Swan, £7.99), which is released as a film this September. We asked him to elaborate:

What inspired you to write the book?

I read an obituary of a man called Henry Gustav Molaison. He had amnesia and was unable to form new memories since undergoing surgery for epilepsy in 1953. As I tried to imagine his situation, I had a mental image of a woman looking in a bathroom mirror in a strange house and not recognising herself. I felt compelled to try and write her story.

I also realised it was through her that I could explore lots of the issues I’d been thinking about for a while, particularly age, power and relationships.

The book explores the theme of trust. At an instinctual level, do we know we can trust someone?

Not really. We get feelings about people and whether they are trustworthy or not, but often they are based on our prejudices. Trusting another human being is always a leap of faith, which is what makes being in love so exhilarating.

Before I Go To Sleep, starring Nicole Kidman and Colin Firth, is released in UK cinemas on 5 September. For your chance to win one of our 50 VIP tickets to see a screening of Before I Go To Sleep with a live interview with author SJ Watson click on the related article below