Distilling consciousness: isolated the underlying brain activity?

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Li et al. How does our brain build its representation of the world surrounding us? What are the neural correlates and mechanisms at the base of conscious experience? This old, yet timely, question is also one of the most challenging to investigate. Indeed, identifying the neural correlates of consciousness (NCC) requires one to disentangle these processes from those that are strictly related but without an actual conscious content. The lack of such discrimination is one of the weaknesses of the experimental paradigm classically used to study NCC, the " minimal contrast " approach (Baars, 1989; Dehaene and Chan-geux, 2011), in which stimulus conditions are held similar while conscious perception varies. Indeed, brain activity registered under the conscious condition may also reflect processes preceding or following conscious perception, but not responsible of it—the so-called " prerequisites " (NCC-pr) and " consequences " (NCC-co) of NCC (Aru et al., 2012). Li et al. (2014) addressed this issue in a recent study published in The Journal of Neuroscience. The authors used magneto-encephalography (MEG) to record brain activity while participants performed a behavioral task designed to give a trial-by-trial measure of subjective awareness confidence of being correct rated on a 4-point scale). This behav-ioral paradigm, a combination of liminal stimulation, forced alternative choice, and trial-by-trial introspection (Lamy et al., 2009; Fleming et al., 2010; Hesselmann et al., 2011), is one of the main strengths of this study, because it gives a separate quantitative measure for each one of the studied neural processes. Considering that NCC contributes by definition only to SUB; that pr-NCC contributes both to SUB and OBJ; and that NCC-co affects SUB and CONF (Aru et al., 2012), a separate measure for each one of these processes permitted the authors to associate the brain activity registered by MEG to specific processes. Furthermore, the isolation of brain activity related to SUB permitted the authors to investigate the correlation between slow cortical potentials (SCPs) measured by MEG (Leistner et al., 2007) and SUB, a link hypothesized by He and Raichle (2009). The authors found enhanced long-lasting event related fields when trials were …