Further GNW simulations showed that ignition could fail to be triggered under specific conditions, thus leading to simulated nonconscious states. For very brief or low-amplitude stimuli, a feedforward wave was seen in the initial thalamic and cortical stages of the simulation, but it died out without triggering the late global activation, because it was not able to gather sufficient self-sustaining reverberant activation (Dehaene and Changeux, 2005). Even at higher stimulus amplitudes, the second global phase could also be disrupted if another
incoming stimulus had been simultaneously accessed (Dehaene et al., 2003b). Such a disruption occurs because during ignition, the Epacadostat manufacturer GNW is mobilized as
a whole, some GNW neurons being active while the rest is actively inhibited, thus preventing multiple simultaneous OTX015 in vitro ignitions. A strict seriality of conscious access and processing is therefore predicted and has been simulated (Dehaene and Changeux, 2005, Dehaene et al., 2003b and Zylberberg et al., 2010). Overall, these simulations capture the two main types of experimental conditions known to lead to nonconscious processing: subliminal states due to stimulus degradation (e.g., masking), and preconscious states due to distraction by a simultaneous task (e.g., attentional blink). The transition to the ignited state can be described, in theoretical physics terms, as a stochastic phase transition—a sudden change in neuronal dynamics whose occurrence depends in part on stimulus characteristics and in part
on spontaneous fluctuations in activity (Dehaene and Changeux, 2005 and Dehaene et al., 2003b). In GNW simulations, prestimulus fluctuations in neural discharges only have from a small effect on the early sensory stage, which largely reflects objective stimulus amplitude and duration, but they have a large influence on the second slower stage, which is characterized by NMDA-based reverberating integration and ultimately leads to a bimodal “all-or-none” distribution of activity, similar to empirical observations (Quiroga et al., 2008, Sergent et al., 2005 and Sergent and Dehaene, 2004). Due to these fluctuations, across trials, the very same stimulus does or does not lead to global ignition, depending in part on the precise phase of the stimulus relative to ongoing spontaneous activity. This notion that prestimulus baseline fluctuations partially predict conscious perception is now backed up by considerable empirical data (e.g., Boly et al., 2007, Palva et al., 2005, Sadaghiani et al., 2009, Supèr et al., 2003 and Wyart and Tallon-Baudry, 2009).