Dog lovers might often wonder if the unspoken connection they feel towards their canine friends is one sided. But new findings published in the journal Advanced Science provide evidence that the feeling is actually mutual.

In the study, scientists discovered that the brain waves of dogs and humans are aligned when they engage in friendly interactions. This phenomenon, known as interbrain coupling or neural synchrony, is well known in humans, underpinning our social experiences, but this is the first time it’s been demonstrated to occur across species.

A long history

To some, this discovery might not come as much of a surprise as dogs, the first animals to be domesticated by humans as early as 40,000 years ago, are considered by many to be more than just pets.

“During the long history of domestication, dogs have developed intimate and effective social interactions with humans,” said Yong Zhang, one of the study’s researchers. Zhang is a professor at Hubei University and the Institute of Genetics and Developmental Biology at the Chinese Academy of Sciences.

“Dogs have evolved to read, understand, and respond to a wide range of human emotional states and communicative signals through behaviors, facial expressions, and even vocal tones, offering an extraordinary level of active companionship that is not often seen in other domesticated or companion animals,” Zhang and his collaborators noted in their paper.  

The researchers were curious if this camaraderie would be reflected in the brain activity recordings of humans and dogs engaging in different social interactions.

They extended their study to examine the interbrain coupling between humans and dogs carrying a genetic variation associated with autism spectrum disorder and explored how it might be restored with the psychedelic drug LSD. Their findings could possibly pave the way for autism treatment if non-hallucinogenic drug analogs are given regulatory approval in the future.  

Human–dog social interactions give rise to interbrain coupling

To observe how well the brain activities of pairs of dogs and humans aligned while interacting with each other, the researchers used electroencephalography (EEG). The non-invasive experiment involved outfitting the dogs and human participants with helmets containing electrodes that recorded the electrical signals generated by brain cells during their social interactions.

The researchers measured the EEG signals of the dogs and humans in different brain regions in three scenarios: in separate rooms without social interactions and with and without petting and mutual gazing — looking into the eyes of the dog — in the same room for five minutes per day.

On the first day of the experiment, the dogs and their human partners were strangers, as the researchers were interested in how interbrain activity coupling changed as they became more familiar with each other.

The researchers found that in all the human–dog pairs, interbrain activity coupling increased from the first day to the fifth day. This finding is analogous to human–human interactions, where interbrain coupling increases the more comfortable two people become with each other.

They also observed that interbrain coupling was highest when mutual gazing and petting were simultaneously initiated by the human partner, compared with petting or mutual gazing alone. Given that domestic dogs perceive their human owners as leaders, the flow of information is from human to dog, reflecting the innate sense of social hierarchy dogs possess.

“As far as we know, interbrain coupling is closely associated with social interactions, where the more and higher quality the social interactions, the higher the interbrain coupling,” Zhang commented.  

Using this model to study autism

In three of the ten dogs, the researchers extended the experiment to ten days and found that interbrain activity coupling plateaued on the seventh day. Zhang says this plateau likely reflects the point at which the pairs had gotten used to the experiment.

“If a human interacts with their pet dog for years, we would assume a stronger interbrain coupling in the pair than that in the human–laboratory dog pair interacting for only a week,” he speculated.    

Because only beagles were studied in the experiment, whether dog breed plays a role in interbrain coupling is unknown for the time being. But the EEG results provide a scientific basis for the close bonds formed between humans and dogs. 

“The stronger interbrain coupling explains, at least partially, why we humans enjoy the companionship of dogs,” Zhang said.

According to Zhang, given their close ties with humans, dogs are ideal animal models of autism. Individuals on the autism spectrum often have difficulties communicating and socially interacting with other people, and dogs can experience similar social deficits when bred to have the same genetics that lead to autism.  

Autism is known to be associated with a change in the SHANK3 gene, which produces a protein that helps maintain the connections between neurons. By introducing an alteration into the Shank3 gene of dogs using the gene-editing tool CRISPR/Cas9, the researchers created a canine model for autism spectrum disorder.

They found that dogs carrying this gene alteration experienced much weaker interbrain coupling with their human partner than the normal dogs in the control group when subjected to the same five-day social experiment.

Psychedelics improve interbrain coupling, but regulatory approval a possible issue 

Motivated by research findings that the psychedelic drug lysergic acid diethylamide, known as LSD, enhances social behavior in mice, Zhang and his team wondered if it could also restore the impaired interbrain coupling between humans and beagles bearing the Shenk3 variation.

They found that 24 hours after administering the drug in an appropriate dose, interbrain coupling in the human–dog pairs gradually increased. This improvement continued up to day five of the experiment without subsequent doses of the drug, but the mechanism for LSD’s effectiveness in rescuing interbrain coupling is currently unclear.

Despite the evidence, gaining approval from public health agencies to treat autism spectrum disorder using an illegal psychedelic drug is likely to be an obstacle. A similar issue was recently faced by researchers seeking to treat post-traumatic stress disorder with combined psychotherapy and the psychedelic drug MDMA.

Although Zhang and his colleagues used the hallucinogenic form of LSD in their pilot study, they propose that non-hallucinogenic analogs of LSD could be engineered for therapeutic purposes. Research has shown that a non-hallucinogenic analog of LSD had an antidepressant-like effect in mice, which is promising.   

They also stressed that their study has a few limitations, such as the small number of dogs and the lab-controlled environment — a more natural setting involving free-moving play between the dogs and their human partners would be ideal, but large movements interfere with the EEG data.

Zhang told us that the next step is to understand how LSD improves interbrain coupling between the dog model of autism and humans so that an effective intervention can be developed. He and his team intend to study non-hallucinogenic LSD analogs in this next phase of their research.  

As the use of psychedelics becomes more mainstream and evidence of their benefits for treating a range of conditions emerge — especially when first-line medications fail — it seems like only a matter of time before these drugs are considered medicine by healthcare practitioners.

Reference: Wei Ren, et al., Disrupted human–dog interbrain neural coupling in autism-associated Shank3 mutant dog, Advanced Science (2024). DOI: 10.1002/advs.202402493

Feature image credit: April Walker on Unsplash