Over the last few months I have been on an extraordinary journey to find out what makes me "me".
I have had my brain scanned, tricked, electrocuted, drugged in a plethora of different experiments in my attempt to find out what it is that gives me the feeling that there is someone inside my head.
Science calls it the search for consciousness. I call it the search for "me".
I was not always aware of myself as a human being separate from those around me.
But at what point does this self-awareness kick-in?
A fascinating experiment at University of Portsmouth indicates that it is between the ages of 18-24 months that a child's brain develops to a stage when it suddenly becomes conscious of itself as an individual.
To test this each child is placed in front of a mirror and encouraged to play.
At some point the child will probably engage with its image in the mirror.
Once this interaction has been established, the carer takes the child away from the mirror and while wiping its nose the carer surreptitiously places a red dot on the child's face in a place that cannot be seen or felt by the child.
The child is then returned to play in front of the mirror.
In one case Owen, aged 16 months, engaged again with his image in the mirror but at no point was he particularly concerned that the image he saw had a large red dot on its face.
In contrast when 22 month old Bethan saw her image in the mirror her hand immediately shot up to her face as she explored the strange spot that she saw on her cheek.
The strong reaction is an indication that Bethan recognises the image and thinks "that's me".
At some point during the brain development something happens which means we become self-aware – but quite what it is still remains a mystery.
Chimpanzee experiments
Is it only humans that have a sense of "I"?
The Mirror Self Recognition Test was devised in the seventies by Professor Gordon Gallup.
Originally he was looking to test consciousness not in children but animals.
"One day I found myself shaving in front of the mirror and it occurred to me: wouldn't it be interesting to see if chimpanzees could recognise themselves in mirrors," he said.
Indeed they do. So how many other animals pass this test for consciousness?
It turns out that we are remarkably alone in the animal kingdom.
In addition to chimpanzees only orang-utans recognize themselves in the mirror.
Of course if you ask most pet-owners they will probably argue vociferously that their dog, cat or hamster is conscious.
Failing the test does not mean that other animals are not self-aware – but a positive result is convincing evidence for a brain that has developed a sense of "me".
Price to pay
It is striking that chimpanzees start to fail the test once they reach 30 years old despite having some 10 or 15 years left to live.
The reason is that self-awareness comes at a cost.
Consciousness allows the brain to take part in mental time travel.
You can think of yourself in the past and even project yourself into the future.
And that is why Gallup believes that in later life chimpanzees prefer to lose their ability to conceive of themselves.
"The price you pay for being aware of your own existence is having to confront the inevitability of your own individual demise.
"Death awareness is the price we pay for self awareness."
But what is it in the brain that makes us conscious?
Probing sleep
The experiment for me that got closest to an answer involved taking a nap at the University of Madison's Centre for Sleep and Consciousness.
Deep sleep is a time when we surrender our consciousness.
But how do you ask the brain questions when it is sleeping?
As Marcello Massimini explained to me I would have to have my brain zapped with electrical pulses in a technique called transcranial magnetic stimulation (TMS).
I was a bit worried about zapping my brain, given that it is a fairly essential tool for doing my mathematics.
But I was assured by Marcello that it was perfectly safe. "I have done it to myself many times".
He still looked fairly normal.
The first part of the experiment involved applying TMS to a small region of my brain when I was awake or conscious.
Electrodes attached to my head record the effect.
Marcello showed me the results: "What is important to notice is that different areas far away from the stimulated site are active at different times in a complex pattern."
The brain is interacting as a complex network.
I was then required to fall asleep and once in deep "stage four" sleep Marcello would zap my brain again.
Unfortunately, I failed this bit of the experiment.
It is very difficult to go to sleep with 60 electrodes on your head, white noise being piped into your ears and a Horizon film crew whispering "is he asleep yet".
Perhaps I was so keen to see the experiment myself that I would not give up on my consciousness.
Despite failing to fall asleep, Marcello showed me the results from more obedient participants.
Complex integration
Unlike in the conscious state, the electrical activity does not propagate through the brain.
It is as if the network is down. The exciting implication is that maybe consciousness is to do with the complex integration in the brain.
Of course it raises the interesting question of whether something like the internet, once it hits a certain threshold, might, too, at some point in the future recognise itself when it looks in the mirror.
As a mathematician my brain rather liked the idea that the mathematical complexity of the neural network in our head might be the key to the secret "me".
Professor du Sautoy will present BBC Two Horizon's The Secret You at 9pm on Tuesday 20 October.
Source: BBC News – http://tinyurl.com/ykpk8ex
