# Functional Magnetic Resonance Imaging in Research on Dog Cognition: A Systematic Review
## 4 Discussion
### Research Articles Considering Auditory Stimuli  
The first studies in this group demonstrated the feasibility of fMRI for exploring canine auditory systems, revealing neural activity in the medial geniculate nucleus, caudal colliculus, and temporal cortex regions when dogs were exposed to broadband noise stimuli. The promising results of this study led the authors to suggest that this modality could become an additional method for the clinical evaluation of auditory function in dogs [45; 46].  
The regions discriminating between two training words were identified in the left temporal cortex, amygdala, left caudate nucleus, and thalamus. Thus, dogs' processing of human words utilizes basic processes like novelty detection, and for some dogs, it may also include auditory and hedonic representations [43]. Dogs' responses to novelty and voice identity were highlighted, with a repetition enhancement effect for voice identity processing found in a secondary auditory region--the caudal ectosylvian gyrus [41]. Long-term fMRI adaptation research by [PERSON] et al. on spoken word processing revealed both lexical meaning-dependent and emotional prosody-dependent responses in near-primary and secondary auditory regions [42]. Another study indicated that dogs could track statistical regularities in speech, with distinct neural activity patterns for structured versus unstructured speech. Lower activity for the structured stream compared to the unstructured stream was noted in a subcortical cluster primarily located in the basal ganglia, encompassing portions of the caudate nucleus and the thalamus [39].  
Dogs can detect naturalness in speech and distinguish between familiar and unfamiliar languages, with specific auditory cortical regions engaged in these processes. For natural speech detection, distinct activity patterns were found for the two languages in the secondary auditory cortex and the precruicate gyrus. Moreover, a more significant difference in responses to familiar and unfamiliar languages was observed in older dogs, suggesting the role of language exposure [38]. Additionally, the research explored how dogs process speech from their owners compared to a neutral speaker. Dogs showed increased activation in the auditory cortex (specifically the secondary auditory caudal ectosylvian gyrus) and the reward center (caudate nucleus) in response to praising speech from their owners, indicating that dogs exhibit attachment behaviors with social bonds, influencing their neural processing of speech [40].  
Notably, several experiments have been conducted combining dogs and humans--an interesting aspect considering dog domestication, raising questions about whether mutual neural mechanisms co-evolved with humans or had an earlier origin. A study found that dogs and humans have similar sound-sensitive brain regions in response to a set of stimuli that included three sound types: human vocalizations, dog vocalizations, and nonvocal environmental sounds, which are recognizable with a background of a silent baseline. It identified cortical sensitivity in perisylvian areas and noted that while both species showed emotional modulation in auditory responses, this effect was more substantial in humans [4]. In a study by [PERSON] et al., dogs and humans observed similar neural sensitivity to voice-like sounds. A left cortical region in dogs, including primary and non-primary areas, responded to voice-like sounds, indicating neural sensitivity to voice likeness in both species [37]. Moreover, dogs show hemispheric bias in processing meaningful words, and can independently process acoustic cues of affective speech intonation, suggesting the functional analogies between canine and human lexical processing. Thus, the neural capacity to process words is not exclusive to humans [35]. Dogs can process human words and speech depending on lexical and emotional valence, which is suspected to play a role in their social bonding.