Anatomical and functional basis of facial expressions and their relationship with emotions in horses

An emotion is defined as the affective response to a stimulus that leads to specific bodily changes, enabling individuals to react to positive or negative environmental conditions. In the absence of speech, emotions in animals are primarily studied by observing expressive components, such as facial expressions. This review aims to analyze the available literature on the influence of environmental stimuli on measurable behaviors in horses, describing the anatomical components involved in perception at the central nervous system level and the efferent pathways that trigger facial muscle contraction or relaxation, thus altering facial expressions. Additionally, articles addressing the function of facial expressions in communication are discussed, emphasizing their role in social interactions in this species. While there is limited research on equine neurophysiology, considering the common structure of the limbic system in most mammals, studies conducted on canines and primates were taken into account. In conclusion, the article underscores the importance of understanding equine facial expressions to assess their emotional states and, by extension, their welfare.