How do we know who we are?
In tonight's Horizon Oxford mathematician Marcus du Sautoy explores this age-old question and comes up with some surprising answers thanks to the latest scientific discoveries about consciousness.
Marcus told me: 'It's great that Horizon is prepared to tackle some of the biggest problems of science. Understanding how the brain gives us a sense of "I" has been one of the greatest challenges for scientists and philosophers for centuries.'
'It was a real privilege to make this programme with Horizon and to journey round the world to see the cutting edge research that is being done to unlock the mysteries of what happens in our heads. On the way I must have had my brain scanned, tricked, drugged, prodded and stimulated in every fashion imaginable. Hopefully the programme will tickle viewers' brains too.'
The programme takes in many of the different ways scientists have found to investigate our sense of ourselves, from the mirror test, devised by Gordon Gallup, that shows when babies can recognise themselves, to the latest research examining that building block of the brain: the neuron.
What's clear about this fascinating topic is that consciousness touches on so many other areas science is only now beginning to tackle in earnest: such as why we sleep, how we make decisions, and how our minds deal with our sense of our own mortality.
'Horizon: The Secret You' airs tonight on BBC Two at 9pm. UPDATE: Watch it now on BBC iPlayer
Marcus du Sautoy is Professor of Mathematics and Simonyi Professor for the Public Understanding of Science at Oxford University.