Big brain evolution: how C. elegans hunts food (Evolution)

by David Turell @, Tuesday, February 26, 2019, 19:32 (577 days ago) @ David Turell

Their few neurons use complex proteins to control the search:

"Perpetually hungry, worms are strategic when it comes to searching for food. The microscopic roundworm Caenorhabditis elegans, or C. elegans, is known to spend up to 20 minutes seeking out snacks in its immediate surroundings before endeavoring to look elsewhere. Now, Rockefeller scientists have identified circuits in the C. elegans brain that underlie this behavior. In a new study, published in Neuron, the researchers describe neural mechanisms responsible for local search, showing that this response can be triggered by either smell- or touch-related cues.

"C. elegans feed on bacteria. And when their environment is teeming with edible microbes, they needn't move much to remain sated. But when food availability decreases, the worms start wiggling around a bit. First, they extensively search the area in which they last encountered sustenance, circling a small region for 10 to 20 minutes. Eventually, however, the worms widen their search perimeter—a strategy that resembles, and is possibly related to, some aspects of human behavior.

"The switch from local to global search has been observed in hungry insects, reptiles, fish, and mammals, suggesting that it may represent a conserved foraging strategy. With a uniquely small and well-characterized nervous system, C. elegans provided Bargmann and her colleagues with handy tools to study the basic brain mechanisms driving this behavior.

"Investigating the longevity of local search, the researchers found that when mechanosensory or chemosensory neurons are stimulated, they act on MGL-1 receptors to modify the activity of ADE or AIA cells for minutes at a time. This cellular modification, in turn, triggers other neurons responsible for local search.

"In short: When food goes missing, worm brain activity is altered for an extended period of time, yielding an extended search period. This process, says López-Cruz, seems to represent the formation of a memory related to changes in food availability.

"'When we take the worm's food away, we are essentially giving it a food-removal stimulus. The behavioral change that follows outlasts that stimulus by fifteen minutes, which is consistent with short-term memory," he says.

"The switch from local to global search, says Bargmann, seems to reflect the process of forgetting."

"'A worm's memory defines the period of local search," she says. "And when it forgets, the animal moves on to longer-range exploration.'"

Comment: Even at this early stage of mental activity, the mechanism is highly complex involving specific protein molecules. Not by chance.

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