Anxiety affects around 40 million adults in the United States, making it the most common mental illness in the country. Data from the Centers for Disease Control and Prevention (CDC) revealed that one in every 10 American men suffer from anxiety.
People with anxiety often find it difficult to adjust to unfamiliar environments and to form firm decisions when the opportunity presents itself, experts said.
"Anxiety may be linked to difficulty in using information about whether the situations we face daily – including relationship dynamics – are stable or not, and deciding how to react," said University of California Berkeley researcher Sonia Bishop.
Having anxiety is serious, and sometimes it's like this: when your friends coax you into going out to have fun, but because the experience is unfamiliar and crowded places don't make you feel good, you refuse. These people, being your friends, may start to tease you and say you've "chickened out."
The word "chicken" has long become synonymous to being cowardly or afraid. But new research suggests that when compared with its connotative meaning, the word provides a different link to anxiety.
The Differences In Behavior
A study featured in the journal Genetics revealed that true chickens – the domestic ones – that are unfamiliar with their surroundings have something in their DNA that may shed light on anxiety in humans.
Choosing chickens for this study instead of mice allowed scientists to take advantage of the "natural" genetics experiment, in which the junglefowl in Asia transformed into the modern domestic fowl.
Dominic Wright of Linköping University in Sweden, the lead author of the study, said most human genetic studies focus on people's chances of developing mental disorder, but they also tend to overlook subtle differences in behavior.
"For example, what makes one person a little more anxious than others? And what makes someone else a little bolder? Animal models like the chicken allow us to address challenging questions like these using controlled breeding experiments," said Wright.
To test anxiety levels in both the red junglefowl and the domestic chicken, scientists observed their activity through an open field test where they were placed in a brightly lit, featureless space they have never been in before.
In the new environment, the red junglefowl spent most of its time frozen with fear in its position, or rapidly moving around. These animals also avoided going to the exposed center of the test arena.
In contrast, domestic chickens in the new environment walked through the whole arena at a less erratic pace.
In conclusion, researchers said that after thousands of years of breeding, domestic chickens have become less fearful and less anxious than the red junglefowl.
Bravery Genes In Chickens
Researchers said the chicken DNA contains properties that make it easier to study, compared to the human or mice DNA. They were able to pinpoint exact genome regions in the chicken which were associated with a certain trait, such as anxiety behavior.
The team created hybrids by cross-breeding White Leghorn chickens and the red junglefowl. These hybrids inherited gene variants from both species, and also displayed different behaviors during the open-field test.
Through genetic sequencing, Wright and his colleagues examined genetic activity in each bird's hypothalamus, the part of the brain that regulates anxiety.
In this region of the brain, they found 10 gene variants that are possibly linked to anxiety behaviors. Six of these 10 candidates are related to brain function and behavior. The gene ADAM10, for instance, is required for proper formation of the brain and for protection against certain neurodegenerative diseases.
Afterwards, the researchers tested whether the 10 gene variants they identified also influenced behavior in mice and humans. The data for the mice study were taken from the Mouse Heterogeneous Stocks cross, a massive mice breeding experiment.
Wright and his team found that mice DNA also contained four of the genes in chickens associated with anxiety.
In humans, three were associated with schizophrenia and bipolar disorder. Anxiety behaviors in humans were not directly measured, but Wright said these may still indirectly reveal links to anxiety as people with bipolar disorder were also diagnosed with anxiety.
"Understanding the genetics underlying the chicken results may provide fundamental insights into animal behavior, including normal behavioral variation in humans," added Wright.