Man and his best friend have something in common: Both get worn out by having to exert self-control and end up making dumb decisions, a new study finds.
Dogs required to sit and stay for 10 minutes were more likely to approach a caged, aggressive dog than when they simply had to wait in a cage for the same amount of time, according to the new research. The findings reinforce the biological nature of self-control, said study researcher Holly Miller of the University of Lille Nord de France.
"When humans are depleted, they are less helpful, more aggressive, gamble more, etc.," Miller told LiveScience in an email, citing a wealth of research regarding the depletion of self-control in humans. "Well, apparently, these consequences also have biological roots. When dogs are depleted, they too are more likely to behave rashly and impulsively."
Sit, stay and self-control
Miller and her colleagues had previously found that dogs give up sooner on a puzzle-solving task after they've had to hold a sit-stay position than if they didn't have to exhibit any self-control. In the same way, humans give up more quickly on puzzle tasks when they're mentally fatigued by having to resist temptations beforehand. As in humans, the drain on self-control could be reversed with a sugary drink.
Self-control research also shows that a mentally depleted person is more likely to take risks and make impulsive gambles than someone who is refreshed. Miller wanted to know if the same was true for pups.
To find out, the researchers had 10 family-owned dogs come into the lab for two variations on the same experiment. In one session, the dog was told to sit and stay on a mat while a distracting hamster (played by a robotic ZhuZhuPet toy) roamed around the floor. In the other session, the dog was caged for 10 minutes, and so did not have to exert self-control.
After the sit-stay session, the dog was brought into a room that held a cage. The cage held a territorial 11-year-old female bull terrier that snarled and barked when it saw the second dog.
The researchers recorded the dog's actions for four minutes, particularly noting where in the room it spent its time. A dog that chose to get closer to the snarling bull terrier's cage was judged as being more impulsive. A dog that kept its distance was judged as more cautious.
The results, published online March 30 in the journal Psychonomic Bulletin & Review, showed a clear difference between a canine that was fresh and one that was dog-tired. Dogs spent 58.9 percent of their time in the portion of the room closest to the angry dog's cage after the sit-stay session, compared with only 41.8 percent after 10 minutes relaxing in a cage, a significant difference.
"There was literally a dog in a kennel barking the equivalent of 'I'm going to kill you! I'm going to beat the s--- out of you!' and depleted dogs would approach this dog. And sit in front of it," Miller said. "But when they were not depleted, they were more cautious, and spent more time farther away."
The results are important for humans and dogs alike, Miller said. People should realize that their tendency to make dumb decisions when tired isn't a sign of personal failure or even something that can be overcome with willpower, she said.
"We tend to believe we should have some superhuman power to avoid these things. We don't," Miller said. "What we do have the ability to do is to plan ahead. To recognize our weaknesses, and to prevent ourselves from having the opportunity to behave in ways that are not optimal for our lives."
For example, in both dogs and humans, a sugary drink seems to provide the brain with the fuel it needs to harness our silliest impulses. A dieter, then, might take care not to avoid food too assiduously, given that a small snack could boost the willpower needed to avoid a big food splurge.
Dog owners should take note, too, Miller said. A family dog that has to restrain its urge to snap at yelling, screaming kids all day may eventually reach a willpower limit and bite, possibly explaining a large proportion of the 4.5 million dog bites in America each year. It's up to people to recognize that dogs need breaks and rest as much as we do, she said.
"The average family dog lives a precarious life. If it inhibits the majority of its natural behavior, (barking, peeing in the house, chewing, etc.) it gets to stay and to live (in the home). If it doesn't — it ends up in the animal shelter. And as humans, I think we owe it to the dogs to help them as best we can."
You can follow senior writer Stephanie Pappas on Twitter . Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on .