Lead researcher Shawn Lockery says that the specialized computer they have identified inside nematodes helps process information about taste and smell and drives a worm's behaviour.
He has revealed that the mechanism involves two closely located chemosensory neurons that act in tandem to regulate behaviour.
While the left neuron controls an on switch, says the researcher, the opposing right one an off switch.
The researcher further says that the sister neurons are situated much like the two nostrils or two eyes of mammals, and together they are known as ASE for antagonistic sensory cues.
Lockery believes that this discovery may one day help scientists develop potential treatments for problems involving taste and smell.
"This computer does some nice calculus, differentiating the rate of change of the strength of various tastes. The worm uses this information to find food and to avoid poisons," Nature magazine quoted him as saying.
Lockery and his colleagues predicted the existence of a derivative-crunching mechanism in the Journal of Neuroscience in 1999, based on the findings that nematodes change directions based on taste and smell.
"In effect, they have two nostrils or two tongues but they are so close together that it is really like having one nostril or one tongue, and yet they find their way around quite effectively. We knew from behavioural experiments that nematodes were doing the same thing that humans were doing, but only from the view of behavioural responses. We didn't know what was going on in the brain," he said.
To get there, the researchers used new imaging and molecular tools, along with some genetic engineering of their worms.
In one experiment, these chemosensory neurons carried a fluorescent protein that changed colour based on neuronal activity, while in another experiment, the neurons carried receptor proteins that recognize capsaicin, the active component in chilli peppers.
The researchers observed that fluorescent proteins changed from blue to yellow when concentrations of salt were high, showing that the left neuron (ASEL) was active as the worms continued forward movement.
When salt levels were reduced, the right neuron (ASER) activated but generated a different behaviour-the worms began a turning, or searching, motion.
"At this point, we wanted to know if these neurons really are controlling behavior. If ASEL really signals that things are getting better, then, if you could artificially activate ASEL the animals ought to go straight like a human going directly toward the pizza. Conversely, if you activate the ASER the animals ought to turn to find their goal," Lockery said.
When the researchers spread the pepper ingredient on turning worms with receptor proteins in the left neuron, they straightened their motion.
Similarly, capsaicin applied to worms with the receptors in their right neurons caused them to change from turning motion to forward crawling.
"We have discovered a tiny, specialized computer inside a primitive round worm. The computer calculates the rate of change of the strengths, or concentrations, of various tastes. The worm uses this information to find food and to avoid poisons," Lockery said
"There are strong indications that a similar device exists in the human nervous system," he added.