Two important theories in cognitive neuroscience are predictive coding (PC) and the global workspace (GW) theory. A key research task is to understand how these two theories relate to one another, and particularly, how the brain transitions from a predictive early state to the eventual engagement of a brain-scale state (the GW). To address this question, we present a source-localization of EEG responses evoked by the local-global task—an experimental paradigm that engages a predictive hierarchy, which encompasses the GW. The results of our source reconstruction suggest three phases of processing. The first phase involves the sensory (here auditory) regions of the superior temporal lobe and predicts sensory regularities over a short timeframe (as per the local effect). The third phase is brain-scale, involving inferior frontal, as well as inferior and superior parietal regions, consistent with a global neuronal workspace (GNW; as per the global effect). Crucially, our analysis suggests that there is an intermediate (second) phase, involving modulatory interactions between inferior frontal and superior temporal regions. Furthermore, sedation with propofol reduces modulatory interactions in the second phase. This selective effect is consistent with a PC explanation of sedation, with propofol acting on descending predictions of the precision of prediction errors; thereby constraining access to the GNW.

Two important theories in cognitive neuroscience are predictive coding and the global workspace theory. A key research task is to understand how these two theories relate to one another, and particularly, how the brain transitions from a predictive early state to the eventual engagement of a brain-scale state (the global workspace). To address this question, we present a source-localisation of EEG responses evoked by the local-global task -an experimental paradigm that engages a predictive hierarchy, which encompasses the global workspace. The results of our source reconstruction suggest three-phases of processing. The first phase involves the sensory (here auditory) regions of the superior temporal lobe and predicts sensory regularities over a short timeframe (as per the local effect). The third phase is brain-scale, involving inferior frontal, as well as inferior and superior parietal regions; consistent with a global neuronal workspace (as per the global effect). Crucially, our analysis suggests that there is an intermediate (second) phase, involving modulatory interactions between inferior frontal and superior temporal regions. Furthermore, sedation with propofol reduces modulatory interactions in the second phase. This selective effect is consistent with a predictive coding explanation of sedation, with propofol acting on descending predictions of the precision of prediction errors; thereby constraining access to the global neuronal workspace. IntroductionTwo important theories in current cognitive neuroscience are predictive coding [Rao1999, Friston2010] and global neuronal workspace theory [Dehaene2011]. The former emphasizes forward and backward exchanges along sensory processing and higher level pathways, with forward connections carrying prediction errors, and backwards connections conveying predictions. In contrast, the latter emphasizes a distinct mode of processing -the global workspace -which has the character of a sustained brain-scale state, into which there is a sharp transition -described as ignition [Dehaene2006].Indeed, King et al. argued for the existence of two distinct modes of processing; the first restricted to sensory areas and the latter the global neuronal workspace. In addition, they have suggested that these two modes are experimentally engaged by the local-global task [King2014]. This is an auditory deviance task in which tones can be unexpected at two different levels of regularity. The first level, which generates the (so called) local effect, reflects regularity at a short temporal frame of reference; i.e. repeated tones. In contrast, the second level, which generates the (so called) global effect, reflects regularity at a longer temporal frame; i.e. repeated sequences of tones.In this way, the local-global task engages a predictive coding hierarchy, with multiple levels at which prediction errors could arise, in much the same vein as proposed by predictive coding [Friston2006]. Global workspace theory would, though, additionally propose the existence of a spatially broad and tem...