Worms can suffer from PTSD: Study

A new study has discovered that like humans, worms are capable of forming associative memories–that is, memories that associate a certain sound or smell or tone of voice with a particular outcome.  Unfortunately, not all memories are positive and researchers discovered that like their human counterparts, worms too can develop PTSD (Post Traumatic Stress Disorder) from traumatic events.

In essence, the researchers discovered that even a very basic animal life form like the C. elegans worm has the ability to learn from past experiences. Furthermore, the research team pinpointed the exact neurons that store these memories and the physiological changes the worms undergo when they retrieve memories to cope with future hardships.

Methodology overview–Not exactly compassionate

“We trained the worms to form associative memories. However, that instead of feeding the worms like with Pavlov’s dogs, we starved them for a day, and instead of ringing a bell, we sprayed a scent that the worms like. We hoped that by linking this odor with hunger, the worms would learn that from now on this pleasant odor signals a distressed situation.”

A day after this “training”, the scientists fed the worms well and sprayed the odor once again. Remarkably, the worms quickly entered into a defensive mode and turned on their stress-protective genes. All this happened as soon as they smelled, what used to be, a pleasant odor. However, when we again subjected the worms to starvation, they were better able to survive the hardship than before their associative-learning training. In a way their PTSD had helped them.”

-Dr. Alon Zaslaver, Hebrew University of Jerusalem’s Genetics Department

The other discovery: Identifying the exact neurons that store memories and the physiological changes the worms undergo when they retrieve memories to cope with future hardships.

“It was wonderful to pinpoint the exact neurons that hold associative memories. It’s very rare that you can look at a neuron and say ‘Here, here is the memory!’

-Dr. Alon Zaslaver

With the help of neuro-genetic techniques, the researchers located these neurons and then genetically engineered new worms whose “fight or flight” neurons could be activated simply by shining a light on them. No need to spray the scent this time–the learning was already hardwired inside them. When researchers activated the neurons where the starvation memories lived, the worms immediately moved into stress mode.

Worm PTSD = Human PTSD

Of course, a similar response is well-known in humans. Post-traumatic stress disorder (PTSD) is a mental disorder that individuals may develop after a traumatic event. In humans, the smallest exposure to a similar scene or a relevant scent can bring back upsetting memories that may trigger anxiety attacks and serious stress disorders.



Journal Reference:  Eliezer, Y., et al. (2019). A Memory Circuit for Coping with Impending Adversity, Current Biology, In Press. https://doi.org/10.1016/j.cub.2019.03.059.

Study: Download PDF

Study Summary


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