Recurrent neural processing

Towards a neural stance on consciousness :: Victor Lamme, University of Amsterdam :: Trends in Cognitive Science, Vol. 10, No. 11, 25 September 2006 ::

Summary and review of the above article

Lamme says that he wishes to approach the question of consciousness from the direction of neuroscience. He asks why it is that some neural processes produce conscious experience, but others do not. Certain distinctions between conscious and unconscious processing have become apparent in neuroscience. Neural correlates of consciousness are apparent in the ventral stream, but not in the dorsal stream, which is responsible for unconscious actions. Neural activity has to pass a certain threshold to become a neural correlate of consciousness.

Trancranial magnetic stimulation can disrupt visual consciousness, and this is thought to relate to the disruption of feedback from higher to lower visual areas. Consciousness seems to require the interaction of feed forward and feedback processes between the higher and lower sensory areas. There is further suggested to be a widespread exchange of information between brain areas processing different aspects of the visual scene.

When consciousness arises

Feed forward/feedback or in other words recurrent interactions that are related to consciousness, also involve prolonged activation of higher-level neurons; for instance the duration of activation of face-selective cells correlates with the visibility of such faces. When recurrent processing involves both the visual cortex and frontoparietal areas, consciousness arises. Feed forward processing by itself can be argued to be insufficient to support consciousness, and thus cannot change the brain in the way that recurrent processing can. The neuroscientist, Tononi, argues that the cortico-thalamic area of the brain constitutes a dynamic core of strong recurrent interactions that are distinct from the processing of brain regions such as the cerebellum.

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