Abstract

After reviewing the literature on current knowledge about consciousness in humans, we present a state-of-the art discussion on consciousness and related key concepts in animals. Obviously much fewer publications are available on non-human species than on humans, most of them relating to laboratory or wild animal species, and only few to livestock species. Human consciousness is by definition subjective and private. Animal consciousness is usually assessed through behavioural performance. Behaviour involves a wide array of cognitive processes that have to be assessed separately using specific experimental protocols. Accordingly, several processes indicative of the presence of consciousness are discussed: perception and cognition, awareness of the bodily-self, self-related knowledge of the environment (including social environment). When available, specific examples are given in livestock species. Next, we review the existing evidence regarding neuronal correlates of consciousness, and emphasize the difficulty of linking aspects of consciousness to specific neural structures across the phyla because high-level cognitive abilities may have evolved independently along evolution. Several mammalian brain structures (cortex and midbrain) are involved in the manifestations of consciousness, while the equivalent functional structures for birds and fishes would likely be the pallium/tectum and midbrain. Caution is required before excluding consciousness in species not having the same brain structures as the mammalian ones as different neural architectures may mediate comparable processes. Finally, specific neurophysiological mechanisms appear to be strongly linked to the emergence of consciousness, namely neural synchrony and neural feedback. Considering the limited amount of data available and the few animal species studied so far, we conclude that different manifestations of consciousness can be observed in animals but that further refinement is still needed to characterize their level and content in each species. Further research is required to clarify these issues, especially in livestock species.