This Tiny Worm Is A Math Wizard

Researchers have found that roundworms decide where to move by integrating and differentiating signals from their environment.

AsianScientist (May 31, 2017) – Even though it only has 302 nerve cells, the roundworm (Caenorhabditis elegans) is able ‘do calculus’ on sensory information to make a decision. These findings have been published in eLIFE.

Animals need to make various decisions based on information from the environment: for example, what to eat, where to go, and who to mate with. Such decision-making is quick when the information is clear but slow when unclear. Research on the neurobiology of decision-making has been performed on monkeys and rodents; however, the details of the mechanisms have been unclear because their brains are too complex, consisting of hundreds of millions of nerve cells.

Focusing instead on the simpler roundworm, a team of researchers led by Dr. Yuki Tanimoto discovered that worms make decisions by mathematically integrating the levels of calcium triggered by an odor.

The research team set up a robotic microscope that simultaneously measures the nerve activity and behavior of a worm in the virtual odor space. The nerve cell’s activity was measured via the concentration of calcium ions in the cell, and the team analyzed the changes in calcium concentration using a mathematical model.

Using the robotic microscope system, they found that, when a worm is trying to find out how to move away from an aversive odor, the calcium concentration in a nerve cell rises slowly according to the integral of the decrease in the odor concentration.

When the calcium concentration reaches to a threshold value, the worm chooses the direction as a ‘deliberate’ decision. In contrast, when a worm happens to move in a direction where the aversive odor increases, the calcium in another nerve cell raises rapidly according to the mathematical differentiation of the odor concentration, producing a rapid ‘reflex’-like response.

In research using the more complex animals, it is known that certain nerve cells in the brain integrate information and make a decision when at a certain threshold. The research team’s result showed that, surprisingly, the worm’s nerve cell also integrates information for decision-making.

The article can be found at: Tanimoto et al. (2017) Calcium Dynamics Regulating the Timing of Decision-making in C. elegans.


Source: Osaka University; Photo: Kimura Lab.
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