My layman thinking on related subject of building brain-like computer is that currently it's possible (although expensive) to build required hardware - i.e. cus

My layman thinking on related subject of building brain-like computer is that currently it's possible (although expensive) to build required hardware - i.e. custom system that will have required number of connected electronic neurons, but I don't see a way to "boot it up". Human brains essentially boots from the DNA - i.e. it's layout and basic functions are predetermined by the DNA and then it gets trained for specifics. Even if we can train machine brain, how do we boot it up to the trainable state?