Experimental and Theoretical Approaches to Conscious Processing

Abstract

Recent experimental studies and theoretical models have begun to address the challenge of establishing a causal link between subjective conscious experience and measurable neuronal activity. The present review focuses on the well-delimited issue of how an external or internal piece of information goes beyond nonconscious processing and gains access to conscious processing, a transition characterized by the existence of a reportable subjective experience. Converging neuroimaging and neurophysiological data, acquired during minimal experimental contrasts between conscious and nonconscious processing, point to objective neural measures of conscious access: late amplification of relevant sensory activity, long-distance cortico-cortical synchronization at beta and gamma frequencies, and "ignition" of a large-scale prefronto-parietal network. We compare these findings to current theoretical models of conscious processing, including the Global Neuronal Workspace (GNW) model according to which conscious access occurs when incoming information is made globally available to multiple brain systems through a network of neurons with long-range axons densely distributed in prefrontal, parieto-temporal, and cingulate cortices. The clinical implications of these results for general anesthesia, coma, vegetative state, and schizophrenia are discussed.

Consciousness supporting networks

“…Similar reductions in external awareness systems have been also shown for non-responsive conditions, such as deep sleep and anesthesia [(for a review see 7)]. Taken together these studies indicate that the two awareness networks mediate (at least partially) conscious ongoing mentation under the functions of a wide 'global neuronal workspace' [1,8]. An increasing list of evidence favors this hypothesis.…”

“…An increasing list of evidence favors this hypothesis. Studies in healthy volunteers on perception in the visual, somatosensory and auditory domains confirm that the subtraction between perceived and unperceived stimuli identifies the lateral frontoparietal associative cortices [8].…”

“…An increasing list of evidence favors this hypothesis. Studies in healthy volunteers on perception in the visual, somatosensory and auditory domains confirm that the subtraction between perceived and unperceived stimuli identifies the lateral frontoparietal associative cortices [8].Over the past fifteen years we have increased our understanding of the neural correlates of awareness [9]. The study of patients with disorders of consciousness provides unique opportunities to determine the sufficient and possibly the necessary conditions for conscious cognition to happen.…”

Synchronization of fronto-parietal beta and theta networks as a signature of visual awareness in neglect

“…Corbetta and Shulman, 2002). However, fronto-parietal networks also are strongly implicated with conscious processing (Dehaene and Changeux, 2011). Neuroimaging and electrophysiological studies of conscious access in humans (e.g., during attention blink, binocular rivalry, inattention blindness, etc.)…”

“…have revealed that consciously accessed stimuli consistently ''ignite'' large-scale prefronto-parietal networks, in contrast to events that have remained out of consciousness (rev. Dehaene and Changeux, 2011;Driver and Vuilleumier, 2001;Rees, 2013). Transcranial magnetic stimulation (TMS) inducing transient dysfunction in parietal or prefrontal areas can prevent conscious perception and even trigger sudden subjective disappearance of visual stimuli (Kanai et al, 2008;Beck et al, 2006;Carmel et al, 2010;Babiloni et al, 2007;Kihara et al, 2011), a reduction of subjective visibility (Rounis et al, 2010), or a hemineglect-like profile (Sack, 2010).…”