Flat-faced dogs are all the rage - and have been for a while. With its wrinkly nose and bat-like ears, the French bulldog - which recently climbed to take the title of the most popular dog breed in the US, according to the American Kennel Club's 2022 registration statistics - is beloved of celebrities like Reese Witherspoon and Megan Thee Stallion.
But while they are cute, some of these animals' distinctive facial features could be affecting their sleep, researchers say.
Researchers from Hungary's Etvs Loránd University used electroencephalogram tests (EEGs) to study the sleep of 92 dogs, attaching electrodes to their heads for three hours to record their brain activity and investigate whether flat-faced dogs suffered from poorer sleep quality than long-nosed breeds.
Because of their narrow nostrils and smaller airways, flat-faced dogs are prone to breathing difficulties. Some veterinarians warn against buying these dogs, which have been bred to exhibit such characteristics.
"We found that the flat-faced dogs slept more in the three hours given to them during the study. More daytime sleep is probably compensation for insufficient sleep at night. But, when we studied the EEG patterns, we got more exciting results than that," researcher Zsófia Bognár said in a statement.
The researchers took note of what happened during the dogs' REM sleep, explaining that an abundance of beta and delta brain waves during REM sleep is generally associated with learning success in dogs and intelligence in humans.
The shorter-nosed - or brachycephalic - dogs had decreased beta waves and increased delta than their longer-nosed peers, and more frequent sleep spindles - bursts of coherent brain activity visible on the EEG - researchers observed.
"This pattern has previously been associated with poorer learning in dogs and loss of white matter in humans," said Ivaylo Iotchev, first author of the study published in the journal Brain Structure and Function.
Experts added that the shorter-nosed dogs spent more time sleeping, "suggesting that the sleep apnea these breeds usually suffer from increases daytime sleepiness."
The researchers said it is likely that the popularity of shorter-nosed dogs is down to their "infant-like traits," including large eyes and heads, high foreheads and small noses, adding "we humans find these traits irresistibly attractive. That's how babies get us to care for them."
"It is possible that the selection of dogs to be infant-like in appearance has also infantilized their brain function," researcher Enik Kubinyi, professor and head of the MTA-ELTE Lendület "Momentum" Companion Animal Research Group and ELTE NAP Canine Brain Research Group, said in a statement.
"But this is a bold assumption for now. What is very likely, however, is that breeding for brachycephalic heads leads to potentially harmful changes in brain function."
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