Some have argued that many of the above neuroimaging paradigms are inappropriately controlled because conscious perception is confounded with increased attention and more extended stimulus processing. Why would this brain state correspond to conscious access? Neurocomputational simulations show that once stimulus-evoked activation has reached highly Is attention a confound or a necessity for conscious access? We 4, 5, 6 and others 7, 8, 24 have suggested that, in addition to vigilance and bottom-up activation, a third factor underlying conscious access is the extension of brain activation to higher association cortices interconnected by long-distance connections and forming a reverberating neuronal assembly with distant perceptual areas. For instance, unmasking of a visual stimulus increases activity in extrastriate areas in tight correlation with subjective Top-down amplification, long-distance reverberation, and reportability How do we consciously perceive a visual stimulus? Many neuroimaging experiments have demonstrated a tight correlation between the conscious visual perception and the activation of striate and extrastriate visual areas 13, 14, 15, 16, 17, 18. We now consider the neural bases of the second, transitive meaning of consciousness, which we term ‘access to conscious report’. awake rather than asleep) is an obvious enabling condition for Early visual activation is not sufficient for conscious report a continuum of states which encompasses wakefulness, sleep, coma, anesthesia, etc.īeing in an appropriate state of vigilance (e.g. To avoid further confusion, we abandon the term and use ‘states of vigilance’ to refer to the non-transitive meaning, i.e. ‘the patient regained consciousness’), and the other transitive (e.g. The term ‘consciousness’ has multiple meanings, one of them intransitive (e.g. Section snippets An enabling condition: vigilance In particular, within non-conscious processing, we distinguish a transient ‘preconscious’ state of activity in which information is potentially accessible, yet not accessed. Based on the recent proposal of a large-scale thalamo-cortical formal network and its simulations 4, 5, we tentatively propose a plausible and testable taxonomy of brain activity states associated with conscious and non-conscious processing. Here, we propose that those apparent contradictions can be resolved by a relevant theorizing of the physiological conditions for conscious processing of sensory stimuli. On the contrary, a controversy has arisen, as some studies suggest that consciousness depends mostly on the thalamus and brain stem, others on early visual areas 2, 3, and yet others on higher prefrontal and parietal association areas 4, 5, 6, 7, 8, 9. Surprisingly, however no coherent picture has emerged from those experiments. Recently, great progress has been achieved by contrasting brain activation images obtained during minimally different experimental conditions, one of which leads to conscious perception while the other does not. Understanding the neuronal mechanisms of consciousness is a major challenge for cognitive neuroscience.
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