Tiny worms make complex decisions with just 300 neurons

A new study has shown that tiny worms with only 302 neurons are capable of making complex decisions, according to its authors in the journal ‘published in Current Biology’.

Scientists have spent decades trying to answer the question of how an animal makes decisions, focusing on the brain cells and connections that might be involved. In the new study they have focused on a different approach, by analyzing behavior and not neurons.

And they were surprised to discover that worms can take into account multiple factors and choose between two different actions, despite having only 302 neurons, compared to approximately 86 billion in humans.

The findings have important implications for how researchers assess motivation and cognitive abilities in animals, the authors note. What’s more, the study shows that complex decision-making capabilities could be encoded in small biological and artificial networks.

“Our study shows that a simple system like the worm can be used to study something complex, like goal-directed decision making. We also show that behavior can tell us a lot about how the brain works.” says senior author Sreekanth Chalasani, an associate professor in the Salk Institute’s Molecular Neurobiology Laboratory.

“Even the simplest systems, like worms, have different strategies and can choose between them, deciding which one suits them in a given situation. -Add-. That provides a framework for understanding how these decisions are made in more complex systems, like humans.”

Whether eating prey or defending its food source, the predatory worm Pristionchus pacificus relies on biting. The team’s challenge was to determine the intentions of the worm when it bites.

The researchers found that ‘P. pacificus chooses between two feeding strategies to bite its prey and competitor, another worm called Caenorhabditis elegans. On the one hand there is the predatory strategy, in which its aim in biting is to kill the prey, and on the other the territorial strategy, in which the bite is used instead to force the ‘C. elegans’ to move away from a food source.

The p. pacificus’ chooses the predatory strategy against the larvae of ‘C. elegans’, which are easy to kill. Instead, ‘p. pacificus’ selects the territorial strategy against ‘C. elegans’ adults, which are difficult to kill and outcompete ‘P. pacificus’ in obtaining food.

To the team, it seemed like the ‘P. pacificus’ weighed the costs and benefits of multiple potential outcomes of an action, behavior that is familiar in vertebrates but unexpected in a worm.

“Scientists have always assumed that worms are simple: when ‘P. pacificus’ bites, we think it always does so with a single predatory purpose says first author Kathleen Quach, a postdoctoral fellow in Chalasani’s lab. “It’s actually versatile and can use the same action, bite the ‘C. elegans’, to achieve different long-term goals. I was surprised to discover that the ‘P. pacificus’ was able to harness what seemed like failed predation into successful, goal-directed territoriality.”

In the future, the scientists intend to determine what cost-benefit calculations of ‘P. pacificus’ are scheduled or flexible. They hope that more research like this will help uncover the molecular underpinnings of decision making.