Neural dynamics of visual awareness investigated by means of Fast Optical Imaging and EEG

The search for the Neural Correlate of Consciousness (NCC, Koch, 2004) is one of the unresolved problems of cognitive neuroscience. Although great efforts have been made to seek to answer this fundamental question, theories about the neural basis of consciousness provide different and competing answers. The heterogeneity of the NCCs interpretations could be due to a methodological gap since so far studies trying to unveil the neural correlates of visual awareness have employed techniques that can reach a high level of resolution only in one dimension (i.e., space or time) resulting to be inadequate to investigate the spatio-temporal dynamics related to conscious vision. The following studies aim to elucidate the controversial search for the neural correlates of visual awareness, by proposing innovative and cutting-edge approaches that allow to move beyond these issues. In the first study, availing of EEG and EROS (Event-Related Optical Signal) techniques we seek to unravel the spatio-temporal dynamics occurring when a visual stimulus enters consciousness. To do so, participants’ brain activity is recorded during the performance of a discrimination task by means of EEG and EROS in separate sessions. EEG allows to investigate the electrophysiological correlates of visual awareness and to identify their exact timing, while EROS permits to disentangle which brain regions and in what order of activation are involved when the stimulus is reported as consciously perceived. Results revealed that when the stimulus entered the consciousness, it elicited a sustained activation in LOC, suggesting that this brain region could represent a reliable neural correlate of consciousness. Interestingly, this sustained activation occurred within the temporal window of VAN (Visual Awareness Negativity), corroborating the idea that LOC could serve as the cortical generator of VAN, which is typically considered a reliable marker of conscious vision. In the second study, EEG signal was decomposed into maximally independent components by means of ICA (Independent Component Analysis) in order to unveil the cortical generators and the time-courses of independent neural sources that significantly contribute to the ERP correlates of visual awareness (i.e., Visual Awareness Negativity and Late Positivity). It emerged that the neural sources of VAN seem to be localized in posterior brain regions, including occipital and temporal cortex, while LP seems to reflect a combination of multiple sources spread over frontal, parietal and occipito-temporal cortex. Overall, the present results provide innovative insights into the search for the neural correlates of visual awareness.