Animals often rely on their sense of smell to locate food. The first one to reach a food source has a better chance of surviving than those who follow. But how exactly does their brain translate scent and then navigate toward it?
In new research published this week in Nature Communications, Hebrew University of Jerusalem neuro-geneticist Alon Zaslaver and his team revealed the complex mathematical calculations animals — even those as simple as worms — do to find their next meal.
Think of the game “Hot or Cold” said Zaslaver in a statement released by the university about the study. “Imagine you’re in a huge dark house and a chocolate cake has just been taken out of the oven. To find the cake, you’ll probably sniff around to see what direction the cake scent is coming from and begin walking in that direction.”
Turns out, worms employ this “Hot or Cold” strategy in their search for food — but with an added twist, said the researchers. First, a neural cell picks up the scent of food and sets the worm on a course. The neural cell remains active and directs the worm to keep moving forward, as the scent intensity keeps getting stronger. If the scent is lost, the cell instructs the worm to stop and look for a better path.
But how does the worm calculate that better path? At this stage, a second neural cell enters into action, operating like a “recalculating route” function in navigation apps, like Waze.
This second cell senses “derivatives,” meaning it calculates whether the odor intensity is positive, and getting “hotter,” or negative, and getting “colder.” If the cell detects a negative derivative, it understands that it’s getting further from the chocolate cake and needs to recalculate its route.
This cell constantly computes new scent data to detect whether the odor intensity is getting stronger or weaker, and charts a path based on these new differential measurements. With a negative reading, the worm will chart a new path whereas a positive one will tell it to stay the course.
This combination is a winning one, according to Zaslaver and Hebrew University graduate students Eyal Itskovits and Rotem Ruach. The two-part system of charting a course based on an initial scent measurement and then conducting followup checks to compute whether scent intensity numbers are going up or down is not only an impressive feat for a worm but a very smart and effective method in the search for food, they said.
“These worms teach us an important lesson,” Zaslaver said.
When looking to solve a problem, a quick solution is often attractive. “However, we need a backup system in place that monitors whether we are indeed moving in the ‘right’ direction, even if that new path differs from the one we originally set out on,” concluded Dr. Zaslaver.
“A worm uses only two neural cells to perform this critical calculation. Imagine what we humans should be able to do with our 100 billion neural cells.”