Some wonder if animals feel the way humans do. Do they feel scared, or are they in pain too? According to researchers, even a wriggly roundworm without eyes, a spine, or a brain may also experience basic emotions.
Worms Feel Basic Emotions Like Fear
Researchers from Nagoya City University in Japan and Northeastern University in the US gave the nematode Caenorhabditis elegans a quick electric zap. According to the new study, the worm's long-lasting response, which looked like it was "running" away, indicates a fear-like brain state.
The species reportedly fled for several minutes after experiencing a brief electric shock. During the experiment, when the subjects felt an electric alternating current for 45 seconds, they ran away for more than 2 minutes at high speeds.
Instead of directly activating the motor system, the worm's negative condition appeared controlled by a particular neural circuit in its basic nervous system. According to the multinational team, these characteristics have recently been recognized as crucial components of emotion, indicating that C. elegans' reaction to an electric shock is similar to fear.
For an animal's response to a stimulus-be it physiological, cognitive, or behavioral- to be classified as emotional, it must satisfy four main criteria: it must last after the stimulus has passed, it must rise or fall with the intensity of the stimulus, it must outweigh other behavioral responses, and it must vary little with the stimulus's nature. C. elegans meets at least three requirements, indicating that even worms may feel "basic" emotions like fear.
When food was provided nearby during this "fearful" condition, the worms ignored it and continued moving quickly, suggesting that the negative state may stifle suitable stimuli.
The research adds to the ongoing discussion of whether or not invertebrates can genuinely experience the first forms of emotion. Invertebrates do, at least to some extent, have persistent positive and negative cognitive states after certain stimuli, according to recent studies on crayfish, bumblebees, and fruit flies.
Charles Darwin himself stated more than a century ago that "even insects express anger, terror, jealousy, and love," however, this was primarily based on our propensity to anthropomorphize and not on any factual research.
Some scientists still believe that emotions cannot be measured objectively and that the term should be entirely abandoned.
Relevance of the Study
The finding indicates that C. elegans may be the perfect example for elucidating how brain circuits link to emotion throughout the animal kingdom. Research on roundworms may aid scientists in understanding how persistently negative feelings that cause mood disorders like depression may develop if there is a shared brain mechanism for emotion regulation among species.
Many roundworm genes, including those that appear to be involved in this "fear-like" reaction, are still present in humans and other animals.
More investigation is required to ascertain whether roundworms like C. elegans exhibit happy emotional states based on rewards like food.
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