Neural correlates of consciousness

Some say that ‘we are our connectome’ – but – it seems that what functionally connects is constantly changing. And according to Wolf Singer timing is important. The temporal is as significant as the spatial. This was the message of Singer’s presentation at Turing Consciousness 2012 in Montreal (video here). He points out that the brain has a small world structure, is massively parallel in communication with co-existance of local and global states. This implies that there must be a mechanism for dynamic routing and rapid reconfiguration of functional networks. This can be accomplish with temporal coordination.


The main material in this talk came from a 2007 paper (citation below). By comparing subliminal and conscious perception using EEG measuring both the power and the synchronization across the frequency range, time course, and scalp location they characterized the neural events that mark consciousness. Here are parts of the discussion section of the paper:


The first (80 ms) electrographic difference between conscious and non-conscious stimulus processing was increased phase-locking of induced gamma oscillations across widely distributed cortical regions. This suggests that early large-scale synchronization could be the event that triggers ignition of the global workspace of consciousness, as postulated by Dehaene and Naccache …


This is interesting because it is the phase-locking that stands out. It seems like local processing and global processing are going on at the same time but not interfering with one another.

Our results show similar activation patterns at individual electrodes in the visible (conscious) and invisible (subliminal) conditions, suggesting that the same neural generators are activated in both cases. In contrast, phase synchronization across electrodes clearly differentiated between conditions, suggesting enhanced long-range coordination of oscillatory activity only in the visible (conscious) condition. Several authors have proposed that conscious perception should be related to coordinated dynamical states of the cortical network, rather than to the activation of specific brain regions. Our results offer direct support for this notion … in line with a recent proposal relating unconscious processing of information with local coordination of neural activity in resonant loops of medium range and relating conscious perception with global coordination of distant neural activity by long-range synchronization. Interestingly, the global long-distance synchronization found in the visible condition was very transient and the earliest event differentiating conscious from nonconscious processing. After this, other electrophysiological measures, such as P3a and theta oscillations, continue to differentiate between consciously and nonconsciously perceived words. This suggests that long-distance synchronization plays a role in triggering the cognitive processes associated with conscious awareness. However, it remains to be clarified through which mechanism long-distance synchronization exerts an impact on subsequent cognitive processes.


The authors distinguish between different aspects of consciousness – its existence, sensory awareness, attentional effects, prediction of near future and connection to working memory.

In contrast to previous experiments, the results of which suggest a late wave of activation as correlate of sensory awareness, our results indicate that access to consciousness is triggered by an early coordination (synchronization) of widely distributed neuronal assemblies starting as early as 80 ms after stimulus presentation … Together, the data suggest that only consciously perceived stimuli give rise to a cascade of processes that have distinct electrophysiological signatures. In summary, these consisted of (1) an early and global phase-locking of gamma oscillations, (2) an enhancement of a P3a-like component of the ERP and of sustained theta oscillations over frontal areas that are likely to reflect transfer and maintenance of the perceived stimuli in working memory, and (3) an enhancement of power and phase-locking of gamma oscillations before test stimulus presentation that may be a correlate of the anticipation of the matching between short-term memory contents and sensory input. …It remains to be clarified whether the early large-scale synchronization is already the neuronal correlate of phenomenal awareness or whether awareness emerges only from the entirety of the processes following this coordinated state.

Melloni L, Molina C, Pena M, Torres D, Singer W, & Rodriguez E (2007). Synchronization of neural activity across cortical areas correlates with conscious perception. The Journal of neuroscience : the official journal of the Society for Neuroscience, 27 (11), 2858-65 PMID: 17360907

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