Worms With Waze: They’re Doing Math to Find Food, Say Hebrew University Researchers

You smell a brownie and follow the scent, finessing your route as you go. So does the nematode, claim Dr. Alon Zaslaver and his neurology team

The lovely C. elegans: Worm neuron does differential equation
Hebrew University

Their math is pretty rudimentary. But worms are solving differential equations, albeit unwittingly, in their search for food, say neurogeneticist Dr. Alon Zaslaver and his students at the Hebrew University of Jerusalem.

He who finds the food first wins, Zaslaver points out in conversation with Haaretz, and concurs that much like us, the worms aren’t aware they’re doing math when searching for food.

The breakthrough research was done on the lovely C. elegans worm, the team reported Thursday in a paper published in a prestigious scientific journal, Nature Communications: “Concerted pulsatile and graded neural dynamics enables efficient chemotaxis in C. elegans”

Do worms even have brains? They do not. But they do have primitive nervous systems which are purely wonderful to work with, Zaslaver enthuses.

You have about 100 billion neurons in your brain, but the nematode C. elegans has 302, exactly. Science knows each and every one of the 302 nematode neurons, exactly. Crucially, the same neurons appear in each and every C. elegans animal, and a given neuron will do the same thing in every individual.

In somewhat higher animals, scientists can't really pinpoint a single neuron target to save their lives. At best they can point to an area of the brain where a neuron that might do something is likely to be. So nematodes are a neuroscientist's delight, and also nobody’s storming the campus to protest worm rights.

To find a brownie

What math is the worm doing? Its calculations are akin to the “hot or cold” game, the team explains.

Imagine your eyes are bound but you can tell there's a brownie in the room. You use your nose and hope to head towards the brownie, practically playing the “Hot or  Cold” game.

If the smell grows stronger, you realize you’re on the right track, and vice versa. If the smell weakens, you’re going the wrong way. In practice, your brain is solving differential equations as you go along.

“If you don’t have eyes to see the cake, if you’re using only your olfactory system – you need a subconscious algorithm,” Zaslaver explains. “The differentials can lead to the direction of the stronger scent, which translates as overall I’m doing good and going in the right direction.”

They showed, he explained, that the nematode has a memory of the differentials sensed along the way.

One neuron actually senses if the differentials are strengthening, and if so, keeps the worm moving forward. If the differentials are weakening, the worm turns in hope of finding a better, shorter path.

However, looking for shortcuts, it may erroneously stray. But here a second neuron comes to the rescue: This nerve cell senses that the "brownie" is farther off and immediately returns it to the straight and narrow.

Worm watching at the Hebrew University
Hebrew University

"The combined mathematical skills of these two neurons lead to an efficient navigation strategy," Zaslaver explains. Ergo, Mathematical Worm finds the food faster than if some other strategy had been used, for instance if done naively a-la the “Hot or Cold” game.

It behaves rather like Waze’s “recalculate route” function. Charting course based on an initial scent measurement, then continuously conducting follow-up checks to compute whether it can find a shorter route is an impressive feat for a worm, say Zaslaver with Hebrew University graduate students Eyal Itskovits and Rotem Ruach. 

Which begs the question of what happens in damaged nematodes that don’t have one of the neurons. The answer, Zaslaver says, is that if one neuron is gone, the other still does its trick but the worm is less efficient.

Yes, there are "super-nematodes" with cell-death impairment, that have extra neurons. We don't know yet whether their mathematical skills  would be superior or "just like of the wild-type," he says.

“These worms teach us an important lesson,” shares Zaslaver, which is that individual nerve cells can accomplish more than we initially thought. "What is the calculation capacity of a neuron? This question keeps many neuroscientists awake days and nights.. Is therea limit at all? Well if a worm performs these critical calculations using  two neural cells,  imagine what we humans should be able to do with our 100 billion neural cells."