Dog owners often wonder what—if anything—is going on when their pooches are sleeping. It turns out they may be learning, according to a new study. Researchers in Hungary trained 15 pet dogs to sit and lie down using English phrases instead of the Hungarian they already knew. Afterward, the scientists attached small electrodes to the dogs’ heads to record their brain activity while they slept. Electroencephalograms (EEGs) showed that during 3-hour naps, the dogs’ brains experienced brief, repeated moments of “slow-wave” brain activity, lasting 0.5 to 5 seconds. These bursts—called sleep spindles because they look like a train of fast, rhythmic waves on EEG recordings—occur during non-REM sleep and are known to support memory, learning, general intelligence, and healthy aging in humans and rats. But this is the first time they’ve been studied in detail in dogs. Like those of humans and rats, the dogs’ sleep spindles occur in short cycles in the 9-hertz to 16-hertz range; in humans and rats, these cycles are associated with memory consolidation. The scientists also discovered that the number of spindle sessions per minute correlated with how well the dogs learned their new, foreign vocabulary, the researchers report this week in Scientific Reports. And—just like in humans—females had more spindle sessions per minute than males and performed better during testing. About 30% of the females learned the new words, compared to about 10% of the males. That suggests, the researchers say, that dogs can serve as models to better understand the function of our own sleep spindles.