Worms may possess basic emotions, new study finds

Brain research is a pivotal aspect of modern life sciences, with emotions as a major focus. Understanding animal emotions has historically been challenging, primarily concentrating on “fear” in mice and rats. However, since the 2010s, scientific papers have started to suggest that even creatures like crayfish and flies exhibit brain functions resembling emotions, particularly regarding behaviors like persistence and valence.

For example, when animals encounter a threat, they may exhibit behaviors such as seeking safety and temporarily ignoring appealing food smells, which hints at rudimentary forms of emotion regulation. Nonetheless, the precise workings of these fundamental “emotion mechanisms” remain largely undiscovered.

An international research team from Nagoya City University in Japan and Mills College at Northeastern University in the U.S. has explored the possibility that the roundworm Caenorhabditis elegans possesses basic “emotions.” Worms were chosen because they have been extensively used to study fundamental functions like perception, memory, and decision-making at cellular and genetic levels. Their findings have been published in GENETICS.

Initially, the team observed that when worms were exposed to alternating current stimulation, they exhibited unexpectedly high-speed movement. Intriguingly, this “running” behavior persisted for one to two minutes even after the electrical stimulation, which only lasted a few seconds, ceased.

Typically, in animals, when a stimulus ends, the response stops promptly to avoid lingering perceptions (e.g., sounds or visual scenes). Therefore, the reaction of “continuing to run after the stimulus stops” is exceptional. Furthermore, during and after the electrical stimulation, the worms disregarded their food bacteria, which are typically vital for environmental cues. This suggests that, in the face of a survival-threatening stimulus like electrical shocks, the worms prioritize escape over food. This behavior implies a basic form of “emotion.”

Through genetic analysis, leveraging the worm’s advantages, the team found that mutants unable to produce neuropeptides (equivalent to human hormones) displayed prolonged continuous running in response to electrical stimulation compared to normal worms. This indicates that the brain actively regulates the duration of the response to danger. Just as in humans, emotions like “excitement,” “happiness,” or “sadness” induced by stimuli may not naturally fade away but are controlled by an active gene-based mechanism.

This study underscores that worms offer valuable insights into the genetic mechanisms underlying primitive “emotions.” Many genes at play in worms have counterparts in humans and other organisms, making worm research pivotal in understanding the genetic basis of “emotions.” This knowledge could have implications for conditions like depression, where negative emotions persist excessively, potentially leading to innovative treatments targeting these newly discovered emotion-related genes.

Source: Nagoya City University

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