Brain: Octopus develops advanced brain, but what does it do?

The nautilus, assumed to be a living example of the ancestors of modern octopus and squid, lacks the brain structures of these animals, yet appears to have both short and long term memory:

Training Nautilus pompilus to associate the smell of food with a blue light, the cephalopods eventually learned to respond to a flash of blue light by extending their tentacles. Then the scientists tested the cephalopods memories with a flash of light 3min, 30min, 1h, 6h, 12h and 24h after training. Amazingly, Nautilus remembered their training for up to an hour before the memory was lost, but then the memory returned 6h later, lasting up to 24h. Nautilus has both short and long term memory, just like modern cephalopods, despite lacking the same brain structures. (The Company of Biologists (2008, June 1). Living Fossils Have Long- And Short-term Memory Despite Lacking Brain Structures Of Modern Cephalopods. ScienceDaily. Retrieved June 3, 2008, from http://www.sciencedaily.com /releases/2008/05/080531074905.htm)

Modern cephalopods (octopus and squid) have complex central nervous systems and coleoid brains, but they must be doing something for the animal other than helping it remember where food is.