Crazed commuters, fretful parents and overwrought executives are not the only ones to experience anxiety — or to benefit from medication for it. The simple crayfish has officially entered the age of anxiety, too.
This presumably was already clear to crayfish, which have been around for more than 200 million years and, what with predatory fish — and more recently, étouffée — have long had reasons to worry.
But scientists in France have documented behavior in crayfish that fits the pattern of a certain type of anxiety in human beings and other animals. The findings, reported Thursday in the journal Science, suggest the external hallmarks of anxiety have been around for a very, very long time — and very far down the food chain.
Beyond that, a precursor of Valium changed the behavior back to normal. That does not mean the crayfish are ready for the therapist’s couch, but it does reinforce the sometimes surprising connections that humans have with other living things.
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The response to threat or danger that the scientists found in crayfish had been documented before in other animals, such as mice, but not in animals without backbones, known as invertebrates, such as insects and crustaceans.
Researchers, including Pascal Fossat and Daniel Cattaert at the University of Bordeaux, reported that after crayfish were exposed to electric shocks, they would not venture out of comfortable dark areas in an elaborate aquarium into scarier (for a crayfish) brightly lit areas.
Crayfish that hadn’t been shocked were more adventurous. They would hesitate then sometimes explore the bright areas.
When the nervous crayfish were given a drug used to treat anxiety — chlordiazepoxide, once sold as Librium — the wariness was eliminated.
In some ways, the pattern is to be expected.
“The whole point of the brain is to predict the future based on past experience,” Cori Bargmann of Rockefeller University wrote in an email after reading the paper.
“Predators and other dangerous conditions have been in existence for hundreds of millions of years, so this is not a new problem for animals to solve,” said Bargmann, who studies behavior in the roundworm, C. elegans, which is far simpler than a crayfish,
As Cattaert said: “If the animal has been facing some danger, it will adapt its behavior for a while to try to estimate future risk.”
This is a more complicated response than fear, which is a reaction to an immediate threat or danger.
Serotonin, a brain chemical that has many roles, increased in the anxious crayfish. Injecting serotonin directly into crayfish made them behave anxiously.
None of this means a crayfish experiences the same kind of untethered, maladaptive distress unconnected to real dangers that modern humans often mean when they talk about anxiety.
This is more like the kind of adaptive alertness, a wariness, that an athlete might experience before a competition, or a soldier on a dangerous patrol, or any human before a blind date.
As to what the crayfish experiences, exactly, science has yet to answer that. It is almost certainly not what a human feels, but, Bargmann said, it makes sense to assume that “complex human emotions and behaviors are built on the simpler strategies the nervous system invented long ago, that are shared between humans and other animals.”
Or, as Cattaert put it: “It’s difficult to know what thinks the crayfish.”