Is Memory Transfer Possible?

Planarians, small flatworms less than a centimeter long, have a rich and controversial history in the science of memory.

It all began in 1955, when biopsychologist James McConnell and his colleague Robert Thompson published a study on “Classical Conditioning in the Planarian.” Surprisingly, McConnell & Thompson showed that these small worms less than the size of a fingernail can learn. By pairing light with electric shock, which causes the worms to contract in self-defense, researchers found that, eventually, planarians learned to associate light with shock, and would contract in response to light even in the absence of shock – a classic example of classical conditioning. These results were later confirmed by other researchers (Halas et al., 1962), but McConnell’s next study was controversial.

Memory Outside the Brain?

You see, planarians are one of those amazing animals which can regenerate parts of their body, like starfish. What is unique about planarians, though, especially for their small size and regenerative abilities, is that they have a centralized nervous system: a head and brain. Even more amazingly, unlike geckos which can regenerate their tails but would die if you chopped their heads off, if you chop a planarian’s head off, or even 90% of its body off, the tip of its tail can regrow a new head and body.

Those who are philosophically-minded might ask: Is a regrown planarian still the same planarian? Does it still have the same memories? What McConnell and colleagues (1959) showed in a follow-up to the classical conditioning study is that, yes, a planarian that loses its head still retains its learning. Somehow, classical conditioning persists even after head-chopping and regeneration, showing that somehow the planarians retained or regrew their memories. These findings, too, have replicated over 50 years later (Shomrat & Levin, 2013).

But wait, aren’t memories stored in the brain? Yes, we think so, which is why these results caused such a storm among memory researchers. But this was only the beginning of McConnell’s planarian controversy.

Cannibalism and Memory Transfer

McConnell’s next study (1962) was titled “Memory Transfer via Cannibalism in Planaria.” Can you guess what happened? After classically conditioning some planaria, McConnell ground them up and fed them to untrained planaria, to see what would happen. Seriously.

The cannibals did not absorb the fear of light that their meals had learned. But amazingly, once these cannibal worms were exposed to the same classical conditioning experiment, they learned fear significantly faster than other worms that had never been exposed to it, almost as if they were re-learning the light-shock association from memory.

That is how McConnell interpreted it, at least. Putting these two findings together – memory retention without a brain, and memory transfer via cannibalism – McConnell was convinced that memories must be stored in the body, and that this meant it was possible to transfer memories from one organism to another.

Does this mean that, like in the video-game series Assassin’s Creed, we might actually have “ancestral memories” lurking in our DNA? Almost certainly not. But McConnell believed memories were stored in RNA, the messenger-cousin which transmits information packed in DNA.

McConnell may have overstepped in the interpretation of his research, but he was onto something.

Researchers Arlene Hartly and colleagues (1964) later replicated the infamous cannibalism findings – sort of. Interestingly, they found that while cannibals who fed on trained planarians managed to learn the threat-association faster, so too did cannibals who fed on untrained planarians. It was less like absorbing memories, and more like absorbing smarts. Therefore, researchers believed that the effect had less to do with true memory transfer, but transfer of something important for memory.

How Is Memory Really Stored?

These studies sparked interesting lines of research injecting RNA into planarians (Jacobson et al., 1966), rats (Rosenblatt et al., 1966), and even recently in snails (Bédécarrats et al., 2018), all finding significant effects on learning and memory in classical conditioning.

Memory Essential Reads

Why You Don't Always Recognize People You Know

How Mirrors and Photos Affect Our Self-Perception

These findings seem to suggest that, as McConnell first intuited, RNA has some role in learning and memory. Scientists do not believe it is the answer to how memory is stored in the body, but it may be a piece in a large, ongoing, mysterious puzzle.

Most biologists, neuroscientists, and psychologists still believe that memory is mainly stored in the brain, but some brainless animals – and formerly brainless planarians – somehow manage to learn and remember things. All of this is to say that, however our brains and bodies store memory, it is very, very, complicated.

Does this mean that memory can be transferred from one organism to another? Currently, there’s no solid evidence supporting this claim. Will it ever be possible? The short answer: We don’t know.