Have you ever talked to your dog while he was sound asleep, wondering if he could hear you? When awake, dogs know how to distinguish a human voice from a canine vocalization and identify certain emotional nuances in sounds. But what about during sleep? Does their brain continue to process this information once asleep? This is precisely what researchers wanted to verify by directly observing the brain activity of dogs during their sleep.
13 dogs under electrodes
To carry out their experiment, these scientists recruited 13 family dogs, aged 1 to 10 years, before equipping them with electrodes on the surface of the skull in order to record their electroencephalogram (EEG), a completely non-invasive method. The researchers then had them listen to different vocalizations, produced either by dogs or by humans, with a positive or neutral tone. From then on, their brain activity was recorded at different times: when they were awake, drowsy, then plunged into non-REM sleep, notably slow wave sleep (or deep sleep).
But how do we know what the brain does with a simple sound? This is where evoked potentials, or ERPs (Event-Related Potentials), come in. The principle is quite clever: after each vocalization, researchers observe the small electrical variation produced by the brain in the hundreds of milliseconds that follow. By repeating the experiment and comparing responses, they can spot reactions specifically related to the sounds heard. This method makes it possible to study how the brain processes auditory information, and offers valuable clues about mechanisms for processing language and vocalizations. In other words, even when the dog seems to have completely stalled, his brain leaves some clues about what he is still processing.
Even when asleep, a dog's brain continues to process sounds
Published in the journal Scientific Reports*, the results of this study are rather intriguing. Even when dozing or sleeping, the dogs didn't seem to process all sounds the same way. Their brains distinguished the vocalizations of their conspecifics from those of humans, while reacting differently depending on whether the sounds had a positive or neutral tone.
The researchers observed these differences at several time points after listening to the vocalizations, with responses that varied depending on sleep state. This suggests that, even when asleep, the dog's brain continues to keep an ear on its surroundings.
However, there is no need to imagine your dog comfortably seated in his basket analyzing your conversation while he sleeps! The study shows neither that he understands the words he hears, nor that he is consciously attentive to the sounds. The researchers simply measured variations in the electrical activity of his brain, not his thoughts or emotions. Furthermore, with only 13 dogs, these results remain exploratory. Above all, they open up an interesting avenue in neurology: the canine brain seems capable of continuing a certain processing of vocal information, even when the rest of the animal is deeply asleep.
* Ele?d, H., Gácsi, M., Bunford, N. et al., “Event-related potentials indicate differential neural reactivity to species and valence information in vocal stimuli in sleeping dogs”, Scientific Report, 13, 14518, 2023.