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Crayfish, similar to organisms of higher complexity, observe their environment, and then make value-based decisions, the research shows. Credit: David D. Yager/Jens Herberholz
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Crayfish make surprisingly complex, cost-benefit calculations, finds a Univ. of Maryland study—opening the door to a new
line of research that may help unravel the cellular brain activity involved in
human decisions.
The Maryland
psychologists conclude that crayfish make an excellent, practical model for
identifying the specific neural circuitry and neurochemistry of decision
making. They believe their study is the first to isolate individual crayfish
neurons involved in value-based decisions. Currently, there's no direct way to
do this with a human brain.
The study will be published in the Proceedings of the Royal Society B.
"Matching individual neurons to the decision making processes in the
human brain is simply impractical for now," explains Univ. of Maryland
psychologist Jens Herberholz,
the study's senior author.
"History has shown that findings made in the invertebrate nervous
systems often translate to more complex organisms. It's unlikely to be exactly
the same, but it can inform our understanding of the human brain, nonetheless.
The basic organization of neurons and the underlying neurochemistry are
similar, involving serotonin and dopamine, for example."
Herberholz adds that his lab's work may inform ongoing studies in rodents
and primates. "Combining the findings from different animal models is the
only practical approach to work out the complexities of human decision making
at the cellular level."
Specific findings and conclusions
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 freely move, the
researchers offered juvenile Louisiana
Red Swamp
crayfish a simultaneous threat and reward: ahead lay the scent of food, but
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 odor of food.
How would the animals react? Did the risk of being eaten outweigh their desire
to feed? Should they "freeze"—in effect, play dead, hoping the
predator would pass by, while the crayfish remained close to its meal—or move
away from both the predator and 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.
Although tail-flipping is a very effective escape strategy against natural
predators, it adds critical distance between a foraging animal and its next
meal.
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 conclude 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 odor was the
strongest, raising the benefit of staying close to the expected reward. A
strong predator stimulus, however, was able to override an attractive food
signal, and crayfish decided to flip away under these conditions.
"Our results indicate that when the respective values of tail-flipping
and freezing change, the crayfish adjust their choices accordingly, thus
preserving adaptive action selection," the researchers write. "We
have now shown that crayfish, similar to organisms of higher complexity,
integrate different sensory stimuli that are present in their environment, and
they select a behavioural output according to the current values for each
choice."
The next step is to identify the specific cellular and neurochemical
mechanisms involved in crayfish decisions, which is more feasible in an animal
with fewer and accessible neurons, Herberholz says. That research is now
underway.
Herberholz's research is funded by grants from the National Science
Foundation and Univ.
of Maryland's Division of
Research.
SOURCE
