Regarding a computer emulating a brain, why not ask me why a computer couldn't emulate my truck and get me to work every morning?
Here's how I analyze this question: A device can be defined in terms of its inputs, process, and outputs.
E.g., a radiator device has the intended purpose of inputting concentrated heat energy and using entropy to output diffuse heat energy. Almost every physical thing in the universe has the side effect of radiating (even a black hole, says Mr. Hawking).
A truck's purpose s to take the inputs of gasoline, driving controls, storage space, and output movement around our world on roads and such of what it's storing.
The brain's function, once again, is to take input from the five senses, and output muscle and hormone controls to the body. The earliest central nervous systems, e.g. c. elegans, had this function, like all more evolved brains of higher complexities, like ours. The brain's "purpose" is to pass on the genes that made it, and among its many ways of doing this is to dazzle mates with mastery in fine arts by controlling muscles that hold paint brushes, musical instruments, etc.
Massimo Pigliucci
WP has argued that emulating a conscious brain in a computer is akin to emulating photosynthesis in a computer. You don't get sugar and you don't get consciousness.
Photosynthesis inputs light, water, and carbon dioxide, and outputs sugars and oxygen. A computer can't emulate this. It can simulate it (like a computer can simulate ping pong), but it won't produce sugar.
A computer, by its most familiar understanding, inputs information (keyboard, camera, mike, Internet, etc.) and outputs information (screen, speakers, etc). The brain, likewise, inputs information (senses) and outputs information (muscle signals). In this sense, the brain and the standard computer are the same. In theory, a computer could replace the brain, inputting senses and outputting muscle control. We already do this in bits, with prosthetic eyes, ears, arms and fingers. Also, in theory, a brain could replace a computer in a robot (e.g. Robocop). This is what we mean when we say the brain
is a computer: information in, information out. What we are arguing is the process inside the brain which produces, as a side effect, consciousness, and whether or not consciousness is computation or an output in and of itself.
The anti-computationalists apparently see consciousness itself as an output of the brain (see this thread's
post #1) like sugar is an output of photosynthesis. I've yet to see them bring home. All I've seen is, essentially, appeals to emotions.