You are what you eat

At least you are if you're a flatworm. An alternative title would be "how to train your flatworm", but that these little dudes can be trained is nowhere near the weirdest thing about them.

In an early experiment, McConnell trained the worms à la Pavlov by pairing an electric shock with flashing lights. Eventually, the worms recoiled to the light alone.  In other experiments, he trained planaria to run through mazes. Eventually, after his retirement in 1988, McConnell faded from view, and his work was relegated to the sidebars of textbooks as a curious but cautionary tale. Many scientists simply assumed that invertebrates like planaria couldn’t be trained, making the dismissal of McConnell’s work easy.

Okay, it's already quite impressive that these guys have enough mental capacity to learn stuff, but maybe not all that surprising considering the claims made about plants. But flatworms do something much, much weirder :

Then something interesting happened when he cut the worms in half. The head of one half of the worm grew a tail and, understandably, retained the memory of its training. Surprisingly, however, the tail, which grew a head and a brain, also retained the memory of its training. If a headless worm can regrow a memory, then where is the memory stored, McConnell wondered. And, if a memory can regenerate, could he transfer it?  

...Planaria are cannibals, so McConnell merely had to blend trained worms and feed them to their untrained peers. (Planaria lack the acids and enzymes that would completely break down food, so he hoped that some RNA might be integrated into the consuming worms.) Shockingly, McConnell reported that cannibalizing trained worms induced learning in untrained planaria.

So flatworms can eat each other to gain their knowledge. Basically they're Sylar from Heroes, only smaller, squishier, and less weird-looking. Not to mention their phenomenal regeneration abilities... I expect Marvel will soon realise that the only answer to Aquaman is Planariaman, whose arms grow into new Planariamen who already know everything the first one knew.

This weird case of mental ingestion isn't limited to flatworms either. The article describes that injecting RNA from trained sea slugs induces learning in untrained sea slugs, and how butterflies can remember things from when they were caterpillars despite having destroyed their brain during their regeneration cycle. It seems that the neural connections in the brain may be more important for the animal to make use of its memories more than for the actual encoding. It would also be interesting to see if plant memories are inherited from cuttings...

I was also reading recently "Other Minds", an excellent little book about the intelligence of octopus. The author describes the phenomena of "split brains" (as does "You Are Not So Smart"), wherein something learned by one hemisphere of the brain is not necessarily automatically learned by the other. In some animals, the creature responds different to the same thing it sees with different eyes - it's as though only half the animal remembers. This is normally not the case in people, but split brains can be medically induced, resulting in something very similar. It's not dissimilar to blindsight, that rare condition where the visual input is processed by the brain but not at the conscious level (which is, perhaps, not so strange as it first appears - after all, you don't remember everything consciously the whole time, but you can recollect things on command pretty well).

It opens up a bunch of questions, of course. In an episode of Star Trek : Deep Space Nine, a character asks, "what is a person but the sum of their memories ?" The answer would seem to be, "a hell of a lot, really". And is the flatworm aware of its ingested memories - inasmuch as flatworms are aware of anything - but not able to act on them, or does forging the neural connections play a role in incorporating the memories into its awareness ? Like how sometimes you may be fully aware of something but do the exact opposite out of habit, like looking for your keys in their usual spot even though you know you put them in the fridge last night because... well, whatever.

And what is it that actually happens when we think ? Why does it feel difficult to remember things sometimes, even though we're not consciously aware of what's happening ? We just sort of instruct our brains to dig up the data and eventually they do - little of this happens consciously, yet it definitely feels difficult somehow. The same goes for thinking in general : sometimes it's extremely hard, but for the life of me I couldn't describe the sensation at all.

Memories Can Be Injected and Survive Amputation and Metamorphosis - Facts So Romantic - Nautilus

The study of memory has always been one of the stranger outposts of science. In the 1950s, an unknown psychology professor at the University of Michigan named James McConnell made headlines-and eventually became something of a celebrity -with a series of experiments on freshwater flatworms called planaria.