# Functional Magnetic Resonance Imaging in Research on Dog Cognition: A Systematic Review
## 4 Discussion
### Research Articles Considering Visual Stimuli  
Research on canine vision using fMRI has revealed insights into how dogs perceive and process visual stimuli, including faces, objects, and dynamic scenes. This group includes some of the earliest studies that served as proof of this concept and demonstrated the feasibility of BOLD imaging in dogs. The first pioneering studies published by [PERSON] et al. detected significant activity in the thalamus and occipital cortex of anesthetized dogs in response to visual stimuli using fMRI [33; 34]. The visual stimulus, which was a grating pattern of black and white bars, triggered significant activity in the lateral geniculate nucleus and throughout the occipital lobe of the cerebral cortex [33]. Subsequent studies were conducted on conscious dogs, proving the feasibility of the method and focusing on detecting activity in the caudate nucleus [19; 32]. Face processing, as a part of visual experiments, provides insights and suggests evolutionary parallels with primates, which can be interpreted in the context of social bonding mechanisms in dogs. A specialized area was identified in the dog temporalcortex that responds preferentially to human and dog faces, indicating that dogs have a distinct neural mechanism for face processing. The face-selective region was detected in the temporal cortex of dogs, and such face selectivity was not found in the dog primary visual cortex. This area was activated more strongly by both human and dog faces than by everyday objects [30]. Furthermore, by comparing responses to human faces and everyday objects, it was confirmed that the bilateral temporal cortex was significantly more activated by faces. These results support the idea of evolutionary conservation in face processing among mammals, which is consistent with previous studies in other species like primates and sheep [29]. On the other hand, dogs exhibited a preference for their own species over human face preference. Species-sensitive visual regions were identified in both human and dog brains (in dogs, the bilateral mid-suprasylvian gyrus), but face-sensitive regions were found only in humans. This study suggests differences in dogs' visual processing compared to humans, where cortical specialization for face perception is more dominant [5]. It is also noteworthy that some studies contributed to understanding how face processing occurs in conjunction with emotional valence and the context of social bonding. It was shown that adjacent but separate areas in the left temporal cortex are involved in processing human and dog faces, with emotional valence influencing activation, but not the distinction between human and dog faces. Furthermore, face familiarity did not influence activation in these areas [27]. A more recent study found that the caudate, hippocampus, and amygdala--mainly implicated in reward, familiarity, and emotion processing, respectively--were activated when dogs viewed familiar faces. The magnitude of activation, correlated with the duration of human-oriented behavior towards the familiar person, provided insights into the neural mechanisms underlying human-dog interactions based on familiarity and emotional context [21]. Research combining fMRI, eye tracking, and behavioral tests indicated that dogs exhibited strong activation in emotional processing regions when viewing their caregiver's face, regardless of emotional expression. Moreover, a stranger's face primarily activated visual and motor areas. This study supported the idea of an attachment-like system in dogs, with caregivers eliciting more significant reward-related neural responses compared to unfamiliar faces [24]. Further research focused on analyzing how dogs process images. Dogs' ability to differentiate between 3D and 2D images [22] and process dynamic visual information [20] was demonstrated. Dogs showed greater activation within the caudate nucleus for the dimension of stimuli, suggesting hedonic neural mechanisms were involved.