Decapitated Worms Retain Old Memories after Regrowing Heads

A small worm called the planarian has a good memory for such a simple organism. The creatures have been shown to retain memories, even after being decapitated and regenerating a whole new head.

The find is the latest work of biologist Michael Levin of Tufts University, who studies the strange properties of the worms. Planaria have remarkable regeneraion abilities, able to be sliced down the the middle or cut into pieces and respawn into new individuals. 

Levin and his colleagues suspected that planarian flatworms were capable of having long-term memory, and they knew the creatures were averse to bright lights and open spaces, so they trained the worms to crawl through a brightly lit area to gain access to food. Success in training the worms to crawl through the space was a sufficient exhibition of memory, according to the researchers. The worms were shown retaining the memory for as long as two weeks.

After decapitating the worms and allowing them to regenerate a new head and brain - a process that also takes two weeks - the worms exhibited evidence of memory retrieval after regenerating a new head.

Why this happens is not clear, though one suggestion is that while the worms' brains control their behavior, some of their memories may be stored elsewhere in their body. Another hypothesis suggests that the worms' original brains may have modified their nervous systems in a way that altered how their brains formed during regrowth, according to a report by The Verge.

The study plays off separate experiments on the worms done in the 1960s. Because of numerous limitations present during the original research, Levin and his team created a custom-designed system that automates the training of the worms. The system addresses time limitations that hinder the worms' learning process. For example, if a human spends one hour a day training one worm, at the end of a 10-hour work day, the sample size is only 10 worms, and each worm in the sample still still has 23 hours to "unlearn" what was taught.

In an email to Nature World News, Levin said the system, which took five years to develop, "trains worms in parallel, on any type of paradigm, and not only tracks their movement (which existing systems could do) but also gives each worm consistent, 24/seven feedback when they are doing the task incorrectly (which no existing technology could do)."

Levin also noted that typical behavior experiments are "notoriously dependent on the experimenter's skill with the system."

"No one does manual training experiments the same way, even if they try," he said, addressing the flaws in prior methods.

"With our device, any lab can have the training done precisely the same way." The system can be used on worms and other small model animals.  

The testing breakthrough enabled the researchers to provide what Levin called "the first fully-objective evidence that memory does indeed survive decapitation in a creature with a true centralized brain."

The research may serve as a model for future work regarding the encoding of specific memories in biological tissues, as well as assist in future biomedicine and stem-cell derived treatments of degenerative brain disorders in humans.

The research is published in The Journal of Experimental Biology.