Scientists have discovered that worms can have „feelings”.

Insights into how short-term stimulation can alter sustained brain activity and their underlying processes.

Brain research is one of the most important fields in the modern life sciences, and „emotion” is one of its main topics. Traditionally, the study of animal emotions has been a complex area, mainly studying fear responses in mice and rats.

However, since the 2010s, scientific papers have increasingly suggested that even crayfish and flies may have brain functions that resemble emotions by focusing on several attributes of behavior such as stability and valence.

For example, when an animal experiences a dangerous situation, such as being attacked by a predator (negative valence), even for a short period of time, the animal’s behavior may be to ignore the smell of an attractive food and stay in a safe place, even if it is hungry. A certain duration (permanence), which is controlled by a primitive emotional pattern.

However, the details of these basic „emotional mechanisms” remain largely undisclosed.

Research on emotions in roundworms

An international research team from Nagoya City University (Japan) and Mills College at Northeastern University (USA) has revealed the possibility that the roundworm Caenorhabditis elegans has basic „emotions”.

Worms are used because worms are used for detailed analysis of basic functions such as perception, memory, and decision-making at the cellular and genetic levels. The team initially discovered that when the worms were subjected to alternating current stimulation, the worms began to move at unexpectedly high speeds.

Description of behavioral responses of worms to electrical stimulation. Credit: Kristina Galatsis

Interestingly, this “running” response persisted for 1–2 min even after electrical stimulation was stopped for a few seconds.

Generally in animals, when a stimulus ceases, the response to that stimulus usually ceases immediately. (Otherwise, the perception of stimuli, such as sounds or visual scenes, is persistent.) Thus, a response that „continues after the stimulus has stopped” is exceptional.

Behavioral and genetic analysis of emotional responses in worms

Furthermore, the team found that the worms ignored their food bacteria during and after electrical stimulation, providing important environmental information. This suggests that while the presence or absence of bacteria in their diet is generally important, the risk posed by electrical shocks as a survival-threatening stimulus is even more important.

In other words, when worms perceive the dangerous stimulus of an electric shock, their highest survival priority is to escape the scene. To achieve this, brain activity is constantly changing, including bypassing „food” that is normally important to avoid danger.

This suggests that the phenomenon of „continuous running of worms due to short-term electrical stimulation” reflects basic „emotions”.

Implications for understanding human emotions

Furthermore, genetic analysis revealed that mutants unable to produce neuropeptides analogous to our hormones, specifically enhancing the worm’s advantage, continued to run longer in response to electrical stimulation compared to normal worms.

This result indicates that the continuum of response to risk is regulated in a timely manner.

In fact, if we experience excitement or fear for too long, it disrupts our daily lives. Thus, the findings suggest that our emotions, such as „excitement,” „happiness,” or „sadness,” triggered by stimuli do not naturally disappear over time, but are regulated by an active mechanism involving genes.

This study demonstrates that using worms can provide detailed insights into the genetic mechanisms underlying primitive „emotions.” Many of the genes that work in worms are known to be present in humans and other species, so studying worms can provide significant clues about the genes involved in „feelings.”

In particular, conditions such as depression, classified as mood disorders, can be interpreted as states of excessive and persistently maintained negative emotions due to an inability to effectively process experienced stimuli. If novel emotion-related genes are discovered through worm research, these genes could become targets for new treatments for emotional disorders.

Reference: Ling Fei Dee, Jared J Young, Keisuke Maruyama, Chota Kimura, Ryoka Suzuki, Yuto Endo, and Goudarou T Kimura, 1023, August 2023, 2028 Genetics.
DOI: 10.1093/genetics/iyad148

This study was funded by the Japan Society for the Promotion of Science, Grant-in-Aid for Research Nagoya City University, National Institute of Natural Sciences, Toyogi Scholarship Foundation, Japanese Government (MEXT) Scholarship, and the RIKEN Center. For Advanced Intelligence Program (for KDK).