C. elegans leaving a lawn of bacteria it can eat. Image credit: Elias Scheer (CC BY 4.0)
When animals forage for food, they show distinct behavioral patterns in their movement. For instance, the nematode worm Caenorhabditis elegans shows two long-term behavioral states when exploring a patch of food: dwelling, when it moves slowly in a small area, and roaming, when it makes quick and wide-ranging movements. The worms will also occasionally suddenly decide to leave a piece of food and go explore the rest of their environment.
Scientists know that the likelihood of the worms either roaming or dwelling is regulated by neurons passing molecules, such as serotonin and dopamine, to one another. However, it is not known how these two long-term behavioral states impact the momentary decision to leave a piece of food, and which mechanisms may regulate this coupling.
To investigate, Scheer and Bargmann tracked the movement of genetically modified C. elegans and characterized their behavior. This revealed that the decision to leave food is not random but a distinct choice that primarily happens when worms are roaming. A characteristic signature of this response was that worms briefly accelerate immediately before leaving.
Following this discovery, Scheer and Bargmann identified sensory neurons that are involved in this process. As well as detecting external sensory cues, these neurons also integrate internal signals, like whether the animal can eat, to specify how often a worm will leave food.
The implications of this research extend beyond the realm of tiny nematodes. This study provides a new framework to examine the relationship between long-term behavior and momentary decision making. Such insights are crucial in understanding brain function across different organisms, including humans. It paves the way for further research into how behavior is regulated on multiple timescales in the brain.
