Discovering the material basis of subjective experience, the heart of the ancient mind-body problem, is a quest pursued by many clinical and neuroscience laboratories. Yet discovering the neuronal correlates of consciousness leaves the question of the exact relationship between excitable (brain) matter and consciousness open. It has frequently been surmised that information theory can link the objective world of physics to the subjective world of our everyday experiences. In this tutorial, we introduce the audience to the modern study of consciousness and then focus on the integrated information theory (IIT).

IIT stems from Gedanken experiments that lead to phenomenological axioms and ontological postulates and provides a quantitative framework from the perspective of information theory. This framework can be used to compute the complexity of any system of causally interacting parts, such as brains, computers or the internet. Many observations concerning the neural substrate of consciousness fall naturally into place within the IIT framework. Among them are the association of consciousness with certain neural systems rather than with others; the fact that neural processes underlying consciousness can influence or be influenced by neural processes that remain unconscious; the reduction of consciousness during dreamless sleep and generalized epileptic seizures; and the distinct role of different cortical architectures in affecting the quality of experience. The theory has significant implications for our view of nature.