A lot of it is simply having enough memory and speed to implement such things.
I'm beyond amazement concerning these things. I have much confidence that we will simulate a human brain some day if not sooner. The algorithm is not that all complicated but we just do not have the raw processing power and amount of memory to do it, now. We probably could do something very simple now but the time operation to compute one "tick" of an artificial human brain would be very slow. We just need more mapping of the brain and for hardware to catch up to the size and computational requirements.
The number of neurons in animals:
List of animals by number of neurons - Wikipedia
"The whole human brain contains 86 billion neurons and roughly 16 billion neurons in the cerebral cortex."