We've lived and slept alongside dogs, our evolutionary besties, for somewhere between 18,000 and 32,000 years. Along the way, we've learned a few things about canine Zzzs: Dogs doze in adorable positions that people can't pull off, snooze for 12-14 hours a day, only cycle through two sleep stages (humans have four), and sometimes suffer from REM Behavior Disorder. Now, here's one more tidbit, courtesy of a new study from Hungary: Dogs, like humans, probably rely on sleep to lock in long-term memories.
Among other functions, sleep (deep sleep in particular) facilitates memory consolidation, the process of converting newly learned information and experiences into long-term memories. Experimental research and case reports have shown that sleeping, in many cases, boosts our memory of facts and faces. On the flip side, skipping sleep can impede our ability to recall what we did yesterday and leave us susceptible to inventing memories of things that never happened.
Our knowledge of sleep and memory is primarily confined to humans, with a few rodent studies for good measure. But, there's a good reason to bring dogs into the mix — beyond the obvious aww-factor. Canis lupus familiaris, the domesticated dog, has emerged as a good model for studying certain waking behaviors in humans. Brain scans, for example, suggest that scents and sounds trigger comparable neural changes in both species. Researchers have also found evidence of episodic memory in dogs, meaning they can form unique, subjective memories that are grounded in time and place, which requires some amount of self-awareness.
So, researchers wanted to see if dogs recall new information better when they sleep on it, like humans do, and if learning that info alters electrical activity in their furry, dozing noggins. Researchers ran two experiments. In the first, one group of dogs was taught and tested on new commands, while other dogs (the controls) rehearsed the same-old sit/stay/lie-down commands they already knew. All of the dogs then slept for three hours, hooked up to non-invasive, dog-specific versions of sleep tests. Afterwards, they were re-tested on their commands. Pre-sleep learning (for the new-command group), researchers found, altered electrical brain activity patterns (EEG) during both deep sleep and REM sleep, in ways predictive of memory performance. And, the dogs' knowledge of their new commands improved after they napped.
In the second experiment, (different) dogs learned new commands. Then, each dog was assigned to do one of the following activities: sleep, play with a toy, go for a walk or learn a second series of new, unrelated commands. In total, the dogs were tested on their commands three times: as soon as they learned them, after their post-lesson activities (napping, playing, etc.), and then once more, a week later.
The results were a little murky, which isn't surprising given the lack of precedent for how to evaluate sleep-dependent memory consolidation in dogs. The dogs who had to learn two sets of new commands didn't improve at all over the course of the three tests. Most of the other dogs, however, performed best when they returned, a week later, for the third test. This suggested to researchers that nighttime sleep, rather than the post-learning nap, bolstered memory consolidation.
The study is preliminary — it's like a knowing wink at a future scientific discovery. Or, as researchers put it, the findings "open up the possibility that dogs' human-analogue social learning skills might be related to sleep-dependent memory consolidation."