> While the octopus has a large central brain in its head, it also has a unique network of smaller ‘brains’ within each of its arms. It’s just what these creatures need to coordinate the mind-boggling complexity of eight prehensile arms and hundreds of sensitive suckers, which provide the octopus with the equivalent of opposable thumbs (roboticists have been taking note).
A neurological network of loosely-coupled semi-autonomous subsystems...
Humans actually have a much more simplified system like this for coordinating fine motor movement. Bunches of neural tissue at each vertebrae and a few other strategic sites around the body can fire independently as reflexes. Also stomach has a large amount of intelligence going on. Second largest concentration after the cranium.
The enteric nervous system is interesting, but I'm not sure I'd call it intelligent. For one thing, you can chop big bits out of it with no adverse effects.
Well you can blow a freaking crowbar through your brain violently enough that it lands almost a hundred feet behind you and yet the lasting effect might not be much worse than a noticeable change in personality
EDIT
"I first noticed the wound upon the head before I alighted from my carriage, the pulsations of the brain being very distinct. The top of the head appeared somewhat like an inverted funnel, as if some wedge-shaped body had passed from below upward. Mr. Gage, during the time I was examining this wound, was relating the manner in which he was injured to the bystanders. I did not believe Mr. Gage's statement at that time, but thought he was deceived. Mr. Gage persisted in saying that the bar went through his head. Mr. G. got up and vomited; the effort of vomiting pressed out about half a teacupful of the brain [through the exit hole at the top of the skull], which fell upon the floor" [0]
[0] Harlow, John Martyn (December 13, 1848). Passage of an Iron Rod Through the Head. Boston Medical & Surgical Journal. 39 (20): 389–93 sourced from wikipedia.
You can mostly do the same for parts of the central nervous system also. [0][1] While you are probably right I'm not sure if the argument actually justifies the conclusion. It could be argued that the more advanced the system, the more it can recover from losing parts by implementing redundancies and adaptation mechanisms.
A neurological network of loosely-coupled semi-autonomous subsystems...