Biologists at Tufts University have removed the head and brain of a worm by decapitation, and then watched as it regenerated both its head and brain — and, somewhat miraculously, the memories stored inside. At first glance, this finding would seem to confirm cellular memory — the theory that data can be somehow stored by cells that are outside of the brain. More research will undoubtedly have to occur before such a highly contested hypothesis is confirmed, however.

The Tufts researchers tested the memory of planarians, simple flatworms that are renowned for their regenerative properties. These worms can be cut up into pieces, and then each piece will grow into a whole new worm. In a previous study, a piece as small as 1/279th of the original worm regrew into a complete organism within a few weeks. This astonishing regeneration is due to a large number of pluripotent stem cells, which make up around 20% of the worm. These adult stem cells, called neoblasts, can become any of the cell types required by the regenerating planarian — including brain cells.

Planarians dislike bright lights and open spaces, but with training they can learn to ignore it. For the Tuft researchers, this training involved placing planarians on a petri dish, with food illuminated by a bright light in the middle. After 10 days, their little brains learned that the bright, open space in the middle of the petri dish wasn’t so bad after all — the food keeps them alive, after all. Their heads and brains were then lopped clean off and allowed to regrow, which takes around 14 days. The regenerated worms were then placed in the same environment, to see which parts of their previous training, if any, they remembered.

According to the researchers, the worms did not immediately remember how to get the food — but after a single, quick training session, they suddenly remembered that they weren’t afraid of bright open spaces any more. It would seem that a single training session was enough to “refresh” their brains with the learned memories. Compare this to the original training process, which took 10 days and lots of training sessions.

As for where these memories are coming from, the researchers don’t really know. They speculate that the memories might be stored elsewhere in the body, perhaps in the neurons that make up the worm’s nervous system (see the network diagram in the image above). It is possible that the nervous system also learns something during training, and then somehow these neurons play a role in the recreation of old memories when the brain is regenerated.

A lot more research will need to be done to work out exactly what’s going on here — and more importantly, whether other animals, including humans, also store memories outside of the brain.

Now read: MIT discovers the location of memories: Individual neurons

Research paper: doi: 10.1242/​jeb.087809 – “An automated training paradigm reveals long-term memory in planaria and its persistence through head regeneration”. Related open-access papers: doi: 10.1242/​bio.20123400 & doi:10.1371/journal.pcbi.1002481