Worms Do Calculus to Find Food
Like humans with a nose for the best restaurants, roundworms also use their senses of taste and smell to navigate. And now, researchers may have found how a worm's brain does this: It performs calculus.
Worms calculate how much the strength of different tastes is changing - equivalent to the process of taking a derivative in calculus - to figure out if they are on their way toward food or should change direction and look elsewhere, says University of Oregon biologist Shawn Lockery, who thinks humans and other animals do the same thing.
Like human visual systems that respond to the presence and absence of light, Lockery and colleagues found that when the left neuron fires as salt concentrations increase, the roundworm continues crawling in the same direction. The right neuron responds when salt concentrations decrease, and the worm turns in search of a saltier location.
Lockery said this is similar to a game of hot-and-cold with a child. But there is one key difference: the worm doesn't need an observer to say if it's getting closer to or farther from the target - the worm calculates the change by itself.
Observing the worm responding to changes in concentration suggested an experiment to see if the worm's brain computes derivatives. The mathematical concept of a derivative indicates the rate at which something, such as salt concentration, changes at a given point in time and space. So Lockery tried to verify that these neurons recognize changes in salt concentration and then tell the worm where food is and where it is not.
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