The quest for animal consciousness

The philosophical debate as to whether or not animals possess consciousness has transcended many thousands of years and yet has a very brief history in science. The answer to this question will depend on the selection of criteria used to assess both objective evidence based on structure and function of the central nervous system and more subjective indications of consciousness dependent on observable behavior. Studies investigating the similarity of EEG patterns, neural function and markers of neuronal activity often indicate a degree of overlap amongst humans and other animals, while observational studies have documented a range of behaviors demonstrated by many species which cannot be ascribed to basic stimulus-response associations and are more likely to reflect conscious processing. The available behavioral evidence suggests a possible hierarchical organization of consciousness within the animal kingdom, based on level of sensory awareness, complexity of communicative abilities and social interaction, and the presence of some higher order abilities such as self recognition in a few species.