Greg Egan 
Zendegi 

Nasim is a young computer scientist, hoping to work on the Human Connectome Project: a plan to map every neural connection in the human brain. But funding for the project is cancelled, and Nasim ends up devoting her career to Zendegi, a computerised virtual world used by millions of people.Fifteen years later, a revived Connectome Project has published a map of the brain. Zendegi is facing fierce competition from its rivals, and Nasim decides to exploit the map to fill the virtual world with better Proxies: the bit-players that bring its crowd scenes to life. As controversy rages over the nature and rights of the Proxies, a friend with terminal cancer begs Nasim to make a Proxy of him, so some part of him will survive to help raise his orphaned son. But Zendegi is about to become a battlefield …