Michael Platt and colleagues at the Center for Cognitive Neuroscience at Duke University have found that a small group of neurons in the dorsal anterior cingulate cortex (ACC) of the primate brain steadily increases its firing rate during foraging until a threshold is reached and the animal moves on.

The experimenters had the rhesus macaque monkeys direct their gaze to selected portions of a computer screen to receive squirts of fruit juice. When the monkeys weren’t getting enough juice, they gazed at another area of the screen (not moving from one tree to the next), but the decision-making process should be the same, Platt said. For the other variable, travel time, the researchers added delays when monkeys chose to leave one resource and move to another, simulating short and long travel times.

The experimental findings matches the predictions of the Marginal Value Theorem of evolutionary ecologist Eric Charnov, developed in 1976. The theory predicts that foragers will leave a designated spot when their intake from a patch begins to match the average possible intake from the surrounding environment.

Platt said the Marginal Value Theorem has been found to apply to worms, bees, wasps, spiders, fish, birds, seals and even plants.

Ref.: “Neuronal basis of sequential foraging decisions in a patchy environment,” Benjamin Y. Hayden, John M. Pearson, Michael L. Platt. Nature Neuroscience,Advance Online, June 5, 2011. doi: 10.1038/nn.2856