Roundworms use their senses of taste and smell to navigate in their environment through taxis, a directional movement to or away from a stimulus. Now, researchers may have found how a worm’s brain does this: calculus.

Is this worm doing Calculus right now?
Worms calculate how much the strength of different tastes is changing (the same as taking a derivative in calculus (the derivative of y=x^2+4x-5 is y=2x+4)) to figure out if they are moving toward food or should change direction according University of Oregon biologist Shawn Lockery, who believes humans and other animals do the same thing.
With the aid of salt and chili peppers, Lockery reached the calculating-worms conclusion by studying two anatomically identical neurons from the worm’s brain that collectively regulate its behavior. These two neurons function like “on” and “off” gates in a computer in response to changes in salt concentration levels.
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. However the worm calculates if it needs to go closer or further 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.
To do so, he artificially activated each neuron with capsaisin, the chemical that makes hot peppers spicy. Worms normally do not natrually detect the chemical compound. Worms with capsaicin applied to the left neuron crawled forward. When the worm’s brain indicated that the current direction of movement lead to increasing salt concentrations, it continued moving in its original direction. But since the worm’s right neuron was activated with capsaicin, it is fooled into thinking the salt levels are decreasing. So the worm changed direction, hoping to find salt elsewhere.
Previous studies have identified “on” and “off” cells in the brains of other chemosensory animals such as fruit flies, cockroaches, frogs, lobsters and rats. As a result of the strong similarities between these regions, more animals could be doing calculus to find food. This could help the many Americans who cannot taste or smell, especially those with Alzheimer’s.
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