There is a theory of Zombie lifespan projection that has been gaining popularity in certain research circles of late. It submits that even as decomposition has liquefied most of the Zombie brain, it can continue to power the Zombie body by keeping the brain stem alive (somehow). Canada’s McGill University’s online resource, The Brain From Top To Bottom, offers a clear breakdown of the human brain’s control over motor function, which – in my opinion – debunks this theory.
McGill explains that even basic movements – walking, looking around, grabbing – require complimentary actions taken by the brain as a whole. It’s akin to a ship’s crew:
“The forward portion of the frontal lobe receives information about the individual’s current position from several other parts, then – like the ship’s captain – issues its commands to Area 6. Area 6 then decides which set of muscles to contract to achieve the required movement, and issues corresponding orders to the primary motor cortex, also known as Area 4.”
In short, it’s beyond debate that the human brain is far too complex, and the human body too large, to function with only a fraction of its synapses firing. Theories based on reptile studies, and brain stem speculation don’t hold water in the face of cold, hard facts.
A Zombie lives as long as its brain – as a whole – is functioning in at least a deminished capacity, and not one second longer.