Toward a Theory of Consciousness

Abstract

Cognitive neuroscience provides us with both clues and paradoxes about the neural substrate of consciousness. For example, we know that certain corticothalamic circuits are essential for conscious experience, whereas cerebellar circuits are not, despite their huge numbers. We also know that consciousness wanes during slow-wave sleep and generalized seizures, despite levels of neural activity that are comparable to wakefulness. To understand why this is so, empirical observations must be related to a theory that says, in a principled manner, what consciousness is and how it can be generated. This chapter introduces the integrated information theory. Starting from phenomenology and making a critical use of thought experiments, the theory claims that consciousness is integrated information. Specifically, (1) the quantity of consciousness is given by the amount of integrated information generated by a complex of elements, and (2) the quality of experience, such as the “redness” of red, is given by the set of informational relationships within that complex. Integrated information (symbol, φ) is defined as the amount of information generated by causal interactions within a complex of elements, above and beyond the information generated independently by its parts. Qualia space (symbol, Q) is a space where each axis represents a possible state of the complex, each point is a probability distribution of its states, and arrows between points represent the informational relationships generated by causal interactions among its elements. Together, the set of informational relationships within a complex specifies a shape in Q that in turn specifies a particular experience. Several observations concerning the neural substrate of consciousness fall naturally into place within the integrated information framework.