It’s not just about the contents : searching for a neural correlate of a state of consciousness ; a commentary on Wolf Singer

Abstract

Global gamma band synchronisation is perhaps the most extensively studied candidate for a Neural Correlate of Consciousness (NCC). Yet despite numerous studies confirming its association with consciousness, it seems to be neither sufficient nor necessary for the presence of all subjective experiences. Analysis of gamma synchronisation studies suggests that it is a correlate of the initial binding of expected, attended, task-dependent contents of consciousness, whereas task-irrelevant contents do not seem to require gamma synchronisation. While discovery of such a content-related NCC is a remarkable achievement for the neurophysiological research of consciousness, it does not fully explain some of the fundamental structural properties of consciousness, namely the temporal and spatial integration of all available experiences into a coherent stream of consciousness. As an alternative, instead of focusing solely on the selected contents of consciousness, the neural mechanisms of the fundamental properties of consciousness could be studied by contrasting states of (un)consciousness. Recent research into the states of consciousness suggests that, for instance, informational complexity is a highly sensitive predictor of the presence of consciousness, possibly reflecting background structural properties of the unity of subjective experiences. As a limiting factor, though, such a state-related NCC does not seem to reflect the phenomenal diversity of the contents of consciousness. Arguably, these limitations could be overcome by devising experimental setups that would simultaneously probe the neural correlates of the contents and the state of consciousness.