I'm Losing My Mind, Luckily I Have A Few Spares

Remember when we talked about octopuses having three hearts?  Well, it turns out that's not their only anatomical anomaly when it comes to using multiple smaller organs to do a task that we associate with a single organ.  We have one heart, they have three.  We have one brain, they have nine.  We have two arms, they have eight.  Wait a second, go back a bit.  Nine brains?  That sounds wrong.  One sounds right, two sounds possible, but nine?  That's just absurd.

Let's figure out where the nine come from.  Well, first we have the brain itself.  It's in the head and it's where all the thinking takes place.  That's brain one, but we'll get back to it in a bit.  Brains two through nine are in the octopus's arms, one for each.  They're not so much brains so much as large nerve clusters, but since they're fully in charge of moving the arms, they qualify as secondary brains.  They're powerful enough that if you chop an arm off an octopus, the arm will still be able to respond to touch in the same way it would have before being detached.  The head-brain tells the octopus what to grab (or touch, or strangle, or eat), but the arm-brains decide how to go about doing it.  Think Evil Dead II, think Idle Hands. Only, you know, with more control from the head-brain.  By quantity, only a third of an octopuses neurons are actually part of the main brain and most of those are part of the optic lobes, while of the remaining two-thirds of the neurons are mostly in the neural clusters of the arms.

Back to the central brain, where the optic lobes contain more than twice as many neurons as the rest of the central brain combined.  Not just that, the optic lobes (which are in charge of the eyes and vision, not to be mistaken for the optic glands, which control aging and sexual maturity, as discussed earlier) are separated from the rest of the brain by the optic stalks.  So, one could make the reasonable statement that the optic lobes are their own brains responsible just for vision.  Which would bring our brain count from nine to eleven.

Don't believe me?  Here's a diagram of the brain of the common octopus:

Click to embiggen, clicky-poppy.

That lump in the middle that looks kind of like a pumpkin?  Well, that and the bits above and below control everything from interpreting touch and taste, to memory and instinct.  Controlling the arms is done off-site, as I mentioned above.  The two things that look like kidneys?  Those are the optic lobes, and as you can see they're not exactly a part of the brain in the way that we'd normally think of it.  They're connected, but not really part of it, if you follow my meaning.  It would be like saying your hands are part of your torso.  Sure, they're connected, but are they really a part of it?  So our octopus brain count is now eleven brains.

So why haven't these eight-armed, triple-hearted, eleven-brained monstrosities taken over the world yet?  Well, despite having eleven brains, they aren't very smart.  Don't take that the wrong way, they are very smart, but it's not like they're eleven times smarter than something with just as much brain.  In fact, octopuses have surprisingly small brains for an animal of their size, which we should probably be glad about given how smart they are with their relatively tiny brains.  How tiny?  Well, depending on the diagram you're looking at, an octopus brain is either the size of their gonads or of their kidneys.  While I know it often seems like guys are thinking with their junk, imagine if our brains were the size of our balls?  We'd be gibbering, drooling messes.  Moreso than we already are.

Octopus brain math: 1 centralized brain + 2 loosely connected lobes + 8 large neural bundles = Smart enough to be dangerous.

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Sources:
Image taken from Cephalove blog post on octopus brain anatomy
National Geographic article on octopus arm-brains
Tree Of Life website article on cephalopod brain terminology
Tree of Life website cephalopod glossary
University of Washington brain fact sheet
Cephalove blog post on octopus brain anatomy
Wikipedia article on the Octopus