The nuts and bolts of animal emotion.

The study of animal emotion, as with its human equivalent, can be confusing due to the complicated and inconsistent use of terminology, and the number of interlinked fields and topics it encompasses. With this review, we aim to provide an up-to-date and, to the best of our knowledge, complete overview of the field of animal emotion, especially intended for new-comers to the field who wish to get a grasp of this field. We start by tackling the terminology and proposing definitions of commonly used terms, and present the different frameworks used for the study of animal emotion. Here, we heavily draw from human literature, as the definitions of animal emotion are derived originally from human research. We follow-up with an overview of current methodologies for the study of animal emotion, in particular the valence dimension of emotion, and include some of the associated limitations linked to these methodologies. We end by pointing out key areas for future research.