Identity

A friend of mine was telling an interesting story the other day about a big, tough brawler, who had a violent streak as long as his biceps were round (my friend is rather eloquent). One day though, this man was knocked out in a bar-room brawl. The trauma he suffered to his head was enough to cause permanent brain damage, and the hospital staff were unsure how he would be affected when (if) he woke. When he came to the next day, he was exactly the same, with one key difference; he was no longer a violent person.
He had lost all desire to fight. He retained all his memories, his personality, his humour and his preferences. He just no longer relished the idea of causing pain or being aggressive.
It raised some questions. I have an idea of "myself," looking out from behind my eyes. It's easy to see where the idea of a soul came from, a sentient person inside a physical body. But now with advances we have made in neuroscience we know that the sense of 'self' is just a series of electro-chemical reactions. One well-timed punch can completely alter a vital part of a personality, just by damaging a little bit of tissue. The protagonist of my friend's story apparently felt no change had occurred, he didn't feel like a different person. He simple no longer felt aggressive.
Buddhism tells us that there is no self. Over 2,500 years before neuroscience discovered the mechanisms, the Buddha was teaching that there is no discrete, we are an aggregate. "I" am just a collection of thoughts, memories, perceptions and responses, that has somehow deluded itself into believing that it is sentient. But there must have been a point in human evolution where we began to develop this sense of self. Do animals experience self? Plants and micro-organisms almost certainly do not, as they have no brain or CNS. But at what point on the continuum of life do we make the distinction. Can we make a distinction?
Solipsists hold that we can only be sure of the existence of our own minds. Maybe they are right. I know that I have a sense of self, but how can I be sure that you do? How can you be sure that I am not just a highly complex conditioned response that resembles a personality, and you are the only person looking out from behind your eyes? How can I be sure that I am not simply a self, imagining itself an exterior existence?
This raises question for computers and machines as well. Will there come a time when a machine becomes self-aware? If the delusion of self is something achieved with increasing complexity, then this is almost a certainty, however far off it may be. Will this identity be there when we turn the machine on? Or will it arise mid-calculation, a self, a person spontaneously coming into being? What would that be like? To wake up, not staring out of my eyes, but into a dark world of input and calculations, not seeing or feeling or hearing but calculating and searching?
Maybe there is something to the Christian idea of a soul. Some entity that explains this self I feel staring out from behind my eyes. Or maybe it is just me, the only self in a universe of conditioned responses. That's a pretty lonely thought.