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Abstract Among the animals on this planet, dogs are uniquely adapted for life with humans, a status that exposes them to risks of human-mediated traumatic experiences. At the same time, some lineages of dogs have undergone artificial selection for behavioral phenotypes that might increase risk or resilience to stress exposure, providing an opportunity to examine interactions between heritable and acquired traits. In a large-scale study (N = 4,497), English-speaking dog guardians reported on their dogs’ life histories, current living environments, and provided observer ratings of dog behavior using the Canine Behavior Assessment and Research Questionnaire (C-BARQ). Our analysis revealed that adverse experiences in the first six months of life, such as abuse and relinquishment, were significantly associated with increased aggression and fearfulness in adulthood, even when accounting for factors such as acquisition source, sex, and neuter status. Additionally, effects of adversity on fearful and aggressive behavior systematically varied at the breed level, suggesting heritable factors for risk and resilience for developing particular phenotypes. Our findings establish that breed ancestry and individual experience interact to show fear and aggressive behavior in pet dogs, confirming that socioemotional behavior is shaped by gene-environment interactions. 

Abstract Dogs and humans have co-evolved for millennia. This provides an opportunity to examine neural adaptations supporting cross-species communication. Previous canine fMRI studies have identified functional activations in response to human voice perception. However, the specific neural pathways involved in dogs’ ability to process and respond to human language remain unknown. This study takes a data-driven approach to examine the brain connectivity supporting bidirectional communication in a large sample of dogs. We examine white matter pathways linking temporal regions, involved in the perception of communicative signals, and frontal regions, responsible for generating communicative responses. Using cortical regions with known axonal connectivity from tract tracing studies as a foundation, we applied probabilistic tractography to measure connectivity patterns in a diverse cohort of dogs (n = 110, 16 breeds). Our findings reveal that, beyond short-range intra-regional connections, consistent large-scale tracts connect the prefrontal, somatosensory, premotor, motor, and temporal lobes across subjects. Hierarchical clustering analysis revealed distinct structural organization, with sylvian regions strongly connected to motor regions and ectosylvian regions linked to higher-order frontal and prefrontal regions. This organization may suggest that the ectosylvian gyrus plays a key role in integrating auditory input with complex cognitive functions, potentially underlying cross-species communication and language processing in dogs. This study elucidates cortico-cortical communication pathways in dogs and contributes to our understanding of the neural basis of lexical processing in the canine brain. 

Does the head tilt observed in many domesticated dogs index lateralized language processing? To answer this question, the present study evaluated household dogs responding to four conditions in which owners provided an increasing number of communicative cues. These cues ranged from no communicative/affective cues to rich affective cues coupled with dog-directed speech. Dogs’ facial responses were first coded manually using the Dog Facial Action Coding System (DogFACS), followed by an in-depth investigation of head tilt behavior, in which AI-based automated analysis of head tilt and audio analysis of acoustic features extracted from communicative cues were implemented. In a sample of 103 dogs representing seven breed groups and mixed-breed dogs, we found significant differences in the number of head tilts occurring between conditions, with the most communicative (last) condition eliciting the most head tilts. There were also significant differences in the direction of the head tilts and between sex groups. Dogs were more likely to tilt their heads to the right, and neutered male dogs were more likely to tilt their heads than spayed female dogs. The right-tilt bias is consistent with left-hemisphere language processing in humans, with males processing language in a more lateralized manner, and females processing language more bilaterally—a pattern also observed in humans. Understanding the canine brain is important to both evolutionary research through a comparative lens, and in understanding our interspecies relationship. 

Although domestic dogs were the first domesticated species, the nature of dog domestication remains a topic of ongoing debate. In particular, brain and behavior changes associated with different stages of the domestication process have been difficult to disambiguate. Most modern Western breed dogs possess highly derived physical and behavioral traits because of intense artificial selection for appearance and function within the past 200 years. In contrast, premodern dogs, including primitive/ancient breeds, village dogs, and New Guinea Singing Dogs, have undergone less intensive artificial selection and retain more ancestral characteristics. Consequently, comparisons between modern and premodern dogs can shed light on brain and behavior changes that have occurred recently in the domestication process. Here, we addressed this question using a voxel-based morphometry analysis of structural MRI images from 72 modern breed dogs and 13 premodern dogs (32 females). Modern breed dogs show widespread expansions of neocortex and reductions in the amygdala and other subcortical regions. Furthermore, cortical measurements significantly predicted individual variation in trainability, while amygdala measurements significantly predicted fear scores. These results contrast with the long-standing view that domestication consistently involves reduction in brain size and cognitive capacity. Rather, our results suggest that recent artificial selection has targeted higher-order brain regions in modern breed dogs, perhaps to facilitate behavioral flexibility and close interaction and cooperation with humans. 

The ability to communicate with conspecifics is an adaptive behavior important for survival and reproduction, particularly in lineages that evolved enlarged brains and complex social behavior. In humans, language is supported by a robust, left-lateralized white matter fiber tract called the arcuate fasciculus, which links Broca’s and Wernicke’s areas, the core neocortical language regions located in the frontal and temporal lobes, respectively1. This tract is also present in chimpanzees, less substantial than in humans and either weakly leftwardly-asymmetric or not asymmetric2. Other mammalian lineages have evolved large brains, complex behavior and social communication in parallel with primates, notably including carnivores. In dogs (Canis familiaris), domestication has almost certainly involved additional selective pressures and environmental factors that have shaped the evolution and development of neural circuits for communication. We report that the dog brain possesses a large, left-lateralized white matter tract that links cortical centers for productive and receptive communication, and that this tract is positively associated with individual variation in receptive vocabulary size.