The subjects were also exposed to everyday sounds and everyday objects, such as a yoga ball, trash bag and cardboard box.
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After analyzing the results, they found that the ones that reacted aggressively had increased levels of vasopressin, a neurohypophysial hormone that has been associated with aggression in humans.
And when they compared the canines from the study with assistance dogs, which are trained to be non-aggressive, they discovered higher levels of oxytocin among the service pooches.
"Seeing high oxytocin levels in assistance dogs is completely consistent with their behavioral phenotype − that they're very, very friendly dogs that are not aggressive toward people or other dogs," co-author Evan MacLean said in a statement.
So, how do you keep your pup from lashing out?
Researchers suggest pet owners expose their four-legged friends to pleasant human interactions on a regular basis.
"Previous work shows dog-human friendly interactions can create a release in oxytocin in dogs,” MacLean said, “and when dogs interact with people, we see that their vasopressin levels go down over time."
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