Washington: Psychologists have found that crayfish make surprisingly complex, cost-benefit calculations -- thus making an excellent, practical model for identifying the specific neural circuitry and neuro-chemistry of human decision-making.
The study at the University of Maryland (UM) is the first to isolate individual crayfish neurons involved in value-based decisions. Currently, there is no direct way to do this with a human brain.
"Matching individual neurons to the decision-making processes in the human brain is simply impractical for now," explains senior study author and UM psychologist Jens Herberholz.
"The basic organisation of neurons and the underlying neurochemistry are similar, involving serotonin and dopamine, for example," says Herberholz.
The experiments offered the crayfish stark decisions - a choice between finding their next meal and becoming a meal for an apparent predator.
In deciding on a course of action, they carefully weighed the risk of attack against the expected reward, Herberholz says.
Using a non-invasive method that allowed the crustaceans to move freely, researchers offered juvenile Louisiana Red Swamp crayfish a simultaneous threat and reward: ahead lay the scent of food and also the apparent approach of a predator.
In some cases, the "predator" (actually a shadow) appeared to be moving swiftly, in others slowly. To up the ante, the researchers also varied the intensity of the odour of food.
To make a quick escape, the crayfish flip their tails and swim backwards, an action preceded by a strong, measurable electric neural impulse.
The specially designed tanks could non-invasively pick up and record these electrical signals. This allowed the researchers to identify the activation patterns of specific neurons during the decision-making process.
The crayfish took decisive action in a matter of milliseconds. When faced with very fast shadows, they were significantly more likely to freeze than tail-flip away.
The researchers concluded that there is little incentive for retreat when the predator appears to be moving too rapidly for escape, and the crayfish would lose its own opportunity to eat.
This was also true when the food odour was the strongest, raising the benefit of staying close to the expected reward, said an UM release.
A strong predator stimulus, however, was able to override an attractive food signal, and crayfish decided to flip away under these conditions.
The study will be published in the Proceedings of the Royal Society B, and is being released online.