Friday, July 13, 2012

Wolf Singer - Consciousness: Unity in Time Rather Than Space?

In this talk from the recent Evolution and Function of Consciousness Summer School ("Turing Consciousness 2012"), Wolf Singer looks at the neuronal correlates of consciousness - Consciousness: Unity in Time Rather Than Space?  Wolf's talk offers support for the Baars' Global Workspace Theory, as well as suggesting that consciousness results from coherence in time (temporal convergence, phase coherence).
Here is the abstract for his talk:

Wolf Singer - Consciousness: Unity in Time Rather Than Space?

Abstract: The search for neuronal correlates of consciousness (NCC) often relies on comparisons between neuronal activation patterns associated with conscious and non-conscious processing, respectively, of physically identical stimuli. This strategy is known as the subtraction method and thought to isolate neuronal processes specific for conscious experience. However, this approach does not allow one to clearly separate the NCC proper from processes that just permit access to consciousness such as fluctuations in excitability at early stages or from processes that follow conscious experience such as storage of perceived items in working memory and response preparation. This problem can be reduced but not eliminated by considering the precise temporal sequence of events, using methods that capture brain activity with high temporal resolution such as time frequency analysis and event related potentials extracted from EEG or MEG signals.
Applying these methods we find as an early NCC a brief burst of oscillatory activity in the beta/gamma frequency range that occurs about 180 ms after stimulus presentation and is synchronized across a widely distributed network of cortical areas. This suggests as NCC not the activation of a particular, higher order cortical area but a dynamic state that is characterized by the coherent activation of a widely distributed network. This agrees with Baars and Dehaene's hypothesis of a work space and also with Sherrington's view that the unity of conscious experience does not require convergence in space (anatomical convergence) but results from coherence in time (temporal convergence, phase coherence). Indications for a special role of precisely synchronized oscillatory responses in the high frequency range have been obtained previously in animal experiments, using the paradigm of binocular rivalry.

      Fries, P., Roelfsema, P.R., Engel, A.K., Koenig, P., and Singer, W. (1997) Synchronization of oscillatory responses in visual cortex correlates with perception in interocular rivalry. Proceedings of the National Academy of Sciences of America. 94(23), 12699-12704
      Singer, W. (1998) Consciousness and the structure of neuronal representations. Phil. Trans. R. Soc. Lond. B 353: 1829-1840
      Engel, A.K., P. Fries, P.Koenig, M. Brecht, and W. Singer (1999) Temporal binding, binocular rivalry, and consciousness. Consciousness and Cognition 8: 128-151 
      Engel, A.K., P. Fries, P. Koenig, M. Brecht, and W. Singer (1999) Concluding Commentary. Does time help to understand consciousness? Consciousness and Cognition 8: 260-268 
      Melloni, L., C. Molina, M. Pena, D. Torres, W. Singer, and E. Rodriguez (2007) Synchronization of neural activity across cortical areas correlates with conscious perception. The Journal of Neuroscience 27(11): 2858-2865
      Melloni, L. and W. Singer (2010) Distinct characteristics of conscious experience are met by large-scale neuronal synchronization. In: E. Perry, D. Collerton, F. LeBeau and H. Ashton (Eds.). New Horizons in the Neuroscience of Consciousness. Advances in Consciousness Research 79. John Benjamins, B.V., Amsterdam 2010, 17-28
      Aru, J., T. Bachmann, W. Singer and L. Melloni (2012) Distilling the neural correlates of consciousness. Neuroscience and Biobehavioral Reviews 36(2): 737-746

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