Study reveals how mutual gaze and petting synchronize human and dog brains, while gene mutations associated with autism in dogs reduce this connection.
In a recent study published in Advanced Scienceresearchers studied cross-species crossbreeding between dogs and humans. They also investigated whether gene abnormalities associated with autism in dogs hinder social interaction between human-dog pairs.
Background
The human-dog bond developed over time, with dogs domesticated for their protective and hunting abilities. They have become valuable members of households, offering companionship and emotional support. Cross-species partnerships create mutual benefit, but rarely approach the extent of communication between humans and dogs. Dogs can read, understand and react to various human emotions and language cues through facial expressions, behaviors and vocal tones. However, the brain mechanisms underlying social communication between species remain unknown.
About the study
In the present study, the researchers investigated the brain processes that enable human-dog communication. They investigated the effect of autism-related gene changes in dogs on social interactions between the two species.
Non-invasive wireless electroencephalograms (EEG) simultaneously detected brain activity in beagle (research canines) and humans during social interactions. To validate the findings, the researchers assessed cross-brain correlations between different brain regions in three conditions. The conditions included no social interactions in separate spaces, with social interaction in one room, and no social engagement in one room. Social interactions included petting and mutual gaze.
The researchers compared cross-brain coupling during full social interactions (mutual gaze + stroking) with partial social interactions (mutual gaze or stroking only) to assess the synergistic effects of mutual gaze and stroking on cross-brain coupling. They also investigated correlations of brain activity between dogs and humans from different trials and recorded the brain activities of the two species during social interactions over five days to assess the impact of social familiarization on cross-brain neural coupling.
The researchers then conducted an additional five-day study to assess durability, or changes in brain-to-brain interactions, over extended periods. Linear regressions explored the association between duration of social interactions and cross-brain activity. Generalized partial directed coherence (GPDC) algorithms assessed the directionality of intrabrain activity coupling.
Researchers developed a canine model of autism spectrum disorder (ASD) with SH3 mutations and multiple ankyrin domain 3 repeat (Shank3) mutations using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated protein 9 (Cas9) genome editing.
Behavioral studies such as the three-chamber test and human-dog interaction experiments revealed autism-like symptoms in the mutants. Over the course of five days, the researchers investigated the cross-brain neural connection between the mutant canines and humans. Theta/beta wave ratios (TBR) showed attention problems in the mutants during social interactions between humans and dogs.
The researchers also investigated the effects of lysergic acid diethylamide (LSD), a psychedelic, on brain function. They gave a single dose of 7.5 µg/kg body weight of LSD intramuscularly and observed its effects after 24 hours.
Results
Petting and mutual gaze resulted in intra-brain synchronization in parietal and frontal brain regions during human-dog interactions, respectively. These brain regions are involved in joint attention. The cross-brain correlation in these dog and human brain regions elicited by mutual gaze or petting alone was much lower than that during combined social interactions, including petting and mutual gaze.
Over the course of five days, the intensity of synchronization increased as the human-dog dyad became more intimate. Linear regression analyzes revealed a strong positive correlation between social contact time, intracerebral activity correlates, and GPDC values. After a week of social contact, logistic regressions revealed that intra-brain correlation in frontal and parietal regions had increased.
Within-brain correlations between humans and dogs across sessions were much lower than within the same interaction sessions. The findings demonstrate that mutual involvement between dogs and humans is crucial for intracerebral neural connections. In human-dog social interactions, the human takes the lead and the dog follows. Mutant canines showed lower attention and eliminated transcerebral connections. A single dose of LSD fixed the problems.
conclusions
The study found that the intra-brain neural synchronies between family dogs and humans are identical to those seen during human-human interactions. The frontoparietal network is essential for the coordination of intracerebral activity and the attention of sensory information. Dogs with Shank3 mutations showed poor brain circuitry and attention, comparable to those with ASD. A single dose of LSD restored impaired intracerebral connectivity and joint attention in mutant dogs, indicating that LSD can improve social impairment in ASD patients.
The findings indicate potential biological markers of intracerebral neural activity for the diagnosis of autism spectrum disorder and the development of engineered non-hallucinogenic LSD analogs to address social deficits. Further research on brain coupling may improve knowledge of the neurological mechanisms that underpin social interactions between typically developing people and those with mental illnesses such as ASD.
