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  • [INTRO ♪]

  • The planarian is a saltwater and freshwater flatworm known primarily for its regenerative abilities.

  • Cut off their tail, and they'll grow it back;

  • cut them in half and they'll become two whole flatwormseven though they have a distinctive head region with a brain in it.

  • What's really amazing is that even after losing its brain, a planarian can remember things from before it was beheaded.

  • Planarians are pretty simple animals, but they do have brains that control things like sensory reception.

  • And this brain is considered a true brain, not just a bundle of neurons

  • it has two lobes, it controls nervous function throughout the body, and it has specialized regions.

  • This means their brains probably look a lot how ours once did.

  • And this makes them a great analog for studying brain evolution, as well as asking fundamental questions about things like memory.

  • It's hard to know what memories a planarian has, of course.

  • But you can train them to perform new, unnatural behaviors, and then see if they retain that memory under different conditions.

  • Planarians have simple needs: they like raw meat, and they dislike light and change.

  • Which ... I get it.

  • They're willing to get over their light aversion for a tasty meal, but if other things change at the same time, they just kind of freak out.

  • Like, if you take them out of petri dishes with smooth glass and put them into textured petri dishes, they are too weirded out at first to go for a piece of liver in the middle with a bright light shining on it.

  • But, if you put the flatworms in textured dishes for a while beforehand, you can passively train them to be familiar with that environment.

  • Then, when you add the spotlight and liver, they go for it quicklyproviding researchers with enough evidence of successful training.

  • And when scientists have done this training regimen, they've found the planarians can retain such memories for at least 14 days.

  • That raises the question, of course: what happens when you cut off their heads?

  • We know that within a week, the flatworms grow new, usable heads they can eat with and everythingand they can make it that long without eating, so they're fine.

  • But, presumably, if you have a brain, that's where your memories areso since the 1950s, scientists have been trying to figure out what happens when the flatworms lose and then regrow their brains.

  • And most strangely, they seem to remember previous training.

  • In a 2013 study, for example, the trained flatworms approached the food faster, even though their training happened with their former heads.

  • The difference between the trained and untrained planarians was not as big as it was pre-decapitation,

  • so the researchers concluded that this memory retention isn't quite one hundred percent.

  • But still, it's bizarre that they could remember the training at all.

  • As for how they retain those memories, wellwe don't really know.

  • One intriguing idea is that memories of certain habitual behaviors are partially transferred to neural tissue outside of the brain.

  • So, somehow there are memories stored in other neurons in the body.

  • Which is just so completely against everything we thought we understood about memories.

  • I mean, we talk aboutmuscle memory”, but even that is thought to occur in the parts of the brain that control how you move your extremities, not in those extremities themselves.

  • A lot more research is needed to fully understand this phenomenon, and to figure out if it's unique to planarians or true of all brainy creatures.

  • Because if human memories also exist outside of our brains in some way, understanding how could lead to better treatments for certain brain injuries, memory loss, or dementias.

  • And that would be some pretty awesome stuff to learn from a headless flatworm.

  • Speaking of learning awesome stuff, if you liked hearing about these amazing flatworms, I have a feeling you'll like the videos you can watch with CuriosityStream.

  • CuriosityStream is a subscription streaming service that offers over 2,400 documentaries and non­fiction titles from some of the world's best filmmakers, including exclusive originals.

  • And they have all sorts of videos that give you a deeper dive into this planet's quirkiest inhabitants.

  • You might check out The Year of the Hedgehog, for exampleit follows these adorable weirdos over the course of a year while explaining what makes them and the other animals they encounter so wonderfully unique.

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  • [OUTRO ♪]

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B1 中級

このヒラムシは脳を切断した後、物事を覚えている (This Flatworm Remembers Things After You Cut Off Its Brain)

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    林宜悉 に公開 2021 年 01 月 14 日