After years of experimenting with crayfish, a team of university psychologists has opened the door to studies of more complex organisms with the goal of eventually understanding the human brain functions responsible for decision-making.
The researchers found that the 3.5 cm-long crustaceans could make a form of value judgment — when confronted with shadows that simulated predators, they were less likely to try to propel themselves to safety if they sensed food was nearby.
“We’ve shown that there’s a balance between avoiding getting killed and getting to a potential food source,” said William Liden, a recent graduate who co-authored the study recently published online in the journal Proceedings of the Royal Society B: Biological Sciences. “We’re showing how an animal reacts to stimuli and how its neural network is set up to make this economic decision.”
The short-term aim of recent crayfish experiments was to isolate the neurons that are activated in the animals during decision-making processes, said psychology professor Jens Herberholz, the study’s senior author. These neurons are activated when a crayfish evaluates a situation and decides to escape.
For the study’s experiments, the researchers bought 259 crayfish from a biological supply company and put them in a tank in a Biology-Psychology Building laboratory where they walked freely down a narrow tunnel.
The researchers then produced shadows in the tank that approached the crayfish at various speeds, tricking each crayfish into thinking it was being approached by a predator and activating its escape response by tail-flipping away.
As the predators approached, however, the crayfish more frequently froze in place instead of scooting off to safety when the researchers enticed them with the scent of crushed shrimp pellets, which the researchers said suggested the animal was capable of measuring values when faced with a decision.
The research team was the first to discover that neurons tied to a crayfish’s escape mechanism reacted to shadows when its first paper was published in 2008. This time around, they focused on what specific stimuli triggered the reaction, hoping to produce a neurological model that other researchers can later use to study the reactions of more complex organisms, Liden said.
“What we were trying to show is not only that crayfish have these cool different responses, but that it’s a great model system to understand this type of response,” he said.
Herberholz, who has worked with crayfish for more than 10 years, said he chose them for the study because they have a relatively basic nervous system yet exhibit complex behavior.
In addition to serving as a good research model for scientists, Herberholz said the crayfish study could help students “at all levels of expertise” learn about the connections between nervous system function and behavior.
But despite the study’s potential to serve as a template for research with more complex organisms, Liden said not to expect a full report on the neurochemistry behind human decision-making any time soon.
“You can’t expect to get 200 people in a room, stick electrodes on them and tell them to touch a hot stove to see what their brain does,” Liden said. “You have to start very simple and work your way up.”
However, study co-author and undergraduate student Mary Phillips said she expected research on other organisms to push forward in full force.
“This value-based decision- making is more difficult to understand in complex organisms, but there’s still a huge market for it,” Phillips said.
Although the research has a long way to go, students in the psychology department are excited about the prospect of probing deeper into the minds of more complex organisms.
“It’s fascinating to think that animals aren’t just about instincts,” senior psychology major Jamie DeFelice said. “To learn that there might be a cognitive process there is really amazing.”
Herberholz said the research team will continue studying the crayfish in hopes of understanding their neural responses in more detail, perhaps by putting some of the crayfish on a fast to see if the elevated level of hunger played a role in the animal’s decision-making process, he said.
“We’ve identified this as a good model, but we want to get a better grasp on what all the mechanisms are,” Herberholz said. “That’s what future researchers will be looking for.”
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