Global gamma-band synchronisation, research into which was largely triggered and continues to be advanced by Prof. Wolf Singer, is one of the most promising NCCs. Synchronisation seems to increase in most cases when a new, task-dependent content of consciousness is formed. Yet a larger number of complications prevents its acceptance as the main NCC, namely: gamma synchronisation does not persist for as long as the contents of consciousness, some of the contents of consciousness emerge without gamma synchronisation being modulated, and, finally, gamma synchronisation may increase in unconscious or unresponsive states of mind. These complications show that gamma-band synchronisation cannot fully account for the existence of a unified stream of consciousness. Given that consciousness is integrated over cognitive time and space, a sufficient and necessary NCC should persist even when some but not all of the experiences cease to exist in time, or change their location. Nevertheless, even though gamma-band synchronisation seems to be neither necessary nor sufficient for all contents of consciousness to arise, it should be regarded as one of the NCCs specifically involved in the binding of new attended experiences. Future research may also develop more accurate characterization of gamma synchronisation, including its spatial scale, precision, and stability (Singer this collection), and certain forms of synchrony might be necessarily accompanied by consciousness; yet such evidence is not currently available.
Given that gamma synchronisation cannot be the only NCC, research efforts and resources should be distributed to search for the other NCCs, some of which might be responsible for the maintenance of already-bound single contents, and some of which might contribute to the unity of the whole stream of consciousness. Research paradigms should be developed that allow simultaneous manipulation and testing of both the contents and the states of (un)consciousness. Most likely, none of the discovered NCCs alone will be necessary and sufficient for all forms of subjective experiences to exist. How many of the neural correlates will be sufficient for the stream of consciousness to flow, and whether the sufficient ones will also be necessary, remains to be studied in future. For now, an exciting program of NCC research should continue searching for the new avenues. Among various proposals, such as a focus on how social interactions and culture modulate neural networks supporting phenomenal contents (Singer this collection), the present one claims that it’s not just about the contents, and that a state of consciousness deserves a treatment of its own.
Acknowledgements
My research is supported by a Wellcome Trust Biomedical Research Fellowship WT093811MA (awarded to Dr. Tristan Bekinschtein).