Nothing in biology is simple. Nothing. Even the simplest things are orders of magnitude more complex than I ever could have imagined from my lofty platonic realm of numbers and functions.
Life is fractal. Every time you zoom in, there is just as much complexity as the previous zoom level.
Complex algorithms are not energy efficient and since the brain is highly energy efficient we must preclude such algorithms from consideration.
From what little I know, I am unwilling to make that assumption, but I do think that starting with a relatively simple algorithmic/mathematical biology-inspired take and slowly ratcheting up the complexity as needed is a reasonable way to proceed.
I posit the relevant details will be equivalent to a few tens of thousand lines of code since the brain is a highly (energy) efficient organ and there is no room for complex algorithms.
But the path towards this goal is going to be anything but simple. To begin with it will need a multiple order of magnitude improvement in computational power. I primarily view this as a hardware problem.