A recent research shows that crayfish feel emotional stress and after a drug which is used to treat anxiety, is administered, they calm down.

The findings suggest something which was never suspected before that even invertebrates experience emotions.

Crayfish is a small, lobster-like creature and is a fresh water invertebrate which, once in a state of deep anxiety, can only come out of it with the help of some tranquilizers which are used to treat people in a similar condition.

The study revealed that the emotions in crayfish are governed by the same chemical transmitters inside its nervous system that are involved in controlling anxiety in humans. This is the reason the anxious crayfish responded to benzodiazepine which is a tranquilizer used to treat anxiety in people, the scientists observed.

The study which was published in the journal Science, involved subjecting the crayfish to a series of mild electric shocks which made them nervous and made them flick their tails which is an escape response.

They also changed their behaviour when compared to crayfish which had not been subjected to electric shocks. Instead of going to the well-lit parts of their tank, the anxious crayfish went to the darker corners as they were afraid of light.

When the stressed crayfish were treated with chlordiazepoxide which is a potent benzodiazepine, they overcame their anxiety and explored the well-lit areas of their tank and showed no abnormal aversion to light.

However, injecting serotonin which is a neurotransmitter into unstressed crayfish caused them to behave in such a way as if they had undergone electric-shock treatment. Serotonin also plays a major role in governing the stress response in humans. This suggests that there is a common origin of anxiety in crayfish and humans, according to the researchers.

Emotions are viewed as something which is unique to humans. But we can often witness "emotions" in other animals, although not all scientists agree on whether they are exactly same as what people feel.