How does an animal make decisions? Scientists have spent decades trying to answer this question by focusing on the brain cells and connections that might be involved. The Salk scientists take a different approach – analyzing behavior, not neurons. They were surprised to find that the worms can consider multiple factors and choose between two different actions, despite having only 302 neurons compared to about 86 billion in humans.
The findings, published in Current biology on March 7, 2022, have important implications for how researchers assess motivation and cognitive abilities in animals. Moreover, the study demonstrates that complex decision-making abilities could be encoded in small biological and artificial networks.
“Our study shows that you can use a simple system like the worm to study something complex, like goal-directed decision-making. We also demonstrated that behavior can tell us a lot about how the brain works” , says lead author Sreekanth Chalasani, an associate professor at Salk’s Molecular Neurobiology Laboratory. “Even simple systems like worms have different strategies, and they can choose between those strategies, deciding which works best for them in a given situation. This provides a framework for understanding how those decisions are made in more complex systems, like humans.”
Whether eating prey or defending its food source, the predatory worm Pristionchus pacificus rests on the bite. The team’s challenge was to determine the worm’s intentions when it bites.
The researchers found that P. peaceful chooses between two foraging strategies to sting its prey and its competitor, another worm called Caenorhabditis elegans: 1) predatory strategy, in which its purpose for biting is to kill prey, or 2) territorial strategy, in which biting is instead used to force C.elegans away from a food source. P. peaceful chooses the predatory strategy against the larvae C.elegans, which is easy to kill. In contrast, P. peaceful selects territorial strategy against adults C.eleganswho is hard to kill and surpasses P. peaceful For alimentation.
For the team, it appeared that P. peaceful weighed the costs and benefits of several potential outcomes of an action – behavior familiar in vertebrates but unexpected in a worm.
“Scientists have always assumed that worms were simple — when P. peaceful bites, we thought it was always for a singular predatory purpose,” says first author Kathleen Quach, a postdoctoral fellow in Chalasani’s lab. ” In fact, P. peaceful is versatile and can use the same action, bite C.elegans, to achieve various long-term goals. I was surprised to find that P. peaceful could turn what seemed like failed predation into successful, goal-oriented territoriality.”
In the future, scientists would like to determine which of the P. peaceful‘Cost-benefit calculations are hard-wired or flexible. They hope that more research like this will help uncover more of the molecular underpinnings of decision-making.
The research was supported by the National Institutes of Health (5R01MH113905), the WM Keck Foundation, the National Science Foundation, Salk Women & Science, and a postdoctoral fellowship from the Paul F. Glenn Foundation.
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