| Crick, F., Koch, C. A framework for consciousness Nature Neuroscience 2003 (6)2:119-126 [pdf] |
| Here we summarize our present approach to the problem of consciousness. After an introduction outlining our general strategy, we describe what is meant by the term 'framework' and set it out under ten headings. This framework offers a coherent scheme for explaining the neural correlates of (visual) consciousness in terms of competing cellular assemblies. Most of the ideas we favor have been suggested before, but their combination is original. We also outline some general experimental approaches to the problem and, finally, acknowledge some relevant aspects of the brain that have been left out of the proposed framework. |
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| Gegenfurtner, K.R. Cortical mechanisms of colour vision Nature reviews 2003 (4):563-572 [pdf] |
| The perception of colour is a central component of primate vision. Colour facilitates object perception and recognition, and has an important role in scene segmentation and visual memory. Moreover, it provides an aesthetic component to visual experiences that is fundamental to our perception of the world. Despite the long history of colour vision studies, much has still to be learned about the physiological basis of colour perception. Recent advances in our understanding of the early processing in the retina and thalamus have enabled us to take a fresh look at cortical processing of colour. These studies are beginning to indicate that colour is processed not in isolation, but together with information about luminance and visual form, by the same neural circuits, to achieve a unitary and robust representation of the visual world. |
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| Rees, G., Kreiman, G., Koch, C. Neural Correlates of Consciousness in Humans Nature reviews Neuroscience 2002 (3):261-270 [html] |
| The directness and vivid quality of conscious experience belies the complexity of the underlying neural mechanisms, which remain incompletely understood. Recent work has focused on identifying the brain structures and patterns of neural activity within the primate visual system that are correlated with the content of visual consciousness. Functional neuroimaging in humans and electrophysiology in awake mokeys indicate that there are important differences between striate and extrastriate visual cortex in how well neural activity correlates with consciousness. Moreover, recent neuroimaging studies indicate that, in addition to these ventral areas of visual cortex, dorsal prefrontal and parietal areas might contribute to conscious visual experience. |
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| Chalmers, D.J. Neural Correlates of Consciousness: Empirical and Conceptual Questions 2000 [html] |
| The search for neural correlates of consciousness (or NCCs) is arguably the cornerstone in the recent resurgence of the science of consciousness. The search poses many difficult empirical problems, but it seems to be tractable in principle, and some ingenious studies in recent years have led to considerable progress. A number of proposals have been put forward concerning the nature and location of neural correlates of consciousness. A few of these include: |
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| Chalmers, D.J. On the Search for the Neural Correlate of Consciousnes Toward a Science of Consciousness II 1998 [html] |
| I'm going to talk about one aspect of the role that neuroscience plays in the search for a theory of consciousness. Whether or not neuroscience can solve all the problems of consciousness singlehandedly, there is no question that it has a major role to play. We've seen at this conference that there's a vast amount of progress in neurobiological research, and that much of it is clearly bearing on the problems of consciousness. But the conceptual foundations of this sort of research are only beginning to be laid. So I will look at some of the things that are going on from a philosopher's perspective and will see if there's anything helpful to say about these foundations. |
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| Zeki, S., Aglioti, S., McKeefry, D., Berlucchi, G. The neurological basis of conscious color perception in a blind patient Proceedings of the National Academy of Sciences USA 1999 (96)24 [html] |
| We have studied patient PB, who, after an electric shock that led to vascular insufficiency, became virtually blind, although he retained a capacity to see colors consciously. For our psychophysical studies, we used a simplified version of the Land experiments [Land, E. (1974) Proc. R. Inst. G. B. 47, 23-58] to learn whether color constancy mechanisms are intact in him, which amounts to learning whether he can assign a constant color to a surface in spite of changes in the precise wavelength composition of the light reflected from that surface. We supplemented our psychophysical studies with imaging ones, using functional magnetic resonance, to learn something about the location of areas that are active in his brain when he perceives colors. The psychophysical results suggested that color constancy mechanisms are severely defective in PB and that his color vision is wavelength-based. The imaging results showed that, when he viewed and recognized colors, significant increases in activity were restricted mainly to V1-V2. We conclude that a partly defective color system operating on its own in a severely damaged brain is able to mediate a conscious experience of color in the virtually total absence of other visual abilities. |
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| Critchley, H.D. & al neural systems supporting interoceptive awareness Nature Neuroscience 189-195 [pdf] |
| Influential theories of human emotion argue that subjective feeling states involve representation of bodily responses elicited by emotional events. Within this framework, individual differences in intensity of emotional experience reflect variation in sensitivity to internal bodily responses. We measured regional brain activity by functional magnetic resonance imaging (fMRI) during an interoceptive task wherein subjects judged the timing of their own heartbeats. We observed enhanced activity in insula, somatomotor and cingulate cortices. In right anterior insular/opercular cortex, neural activity predicted subjects' accuracy in the heartbeat detection task. Furthermore, local gray matter volume in the same region correlated with both interoceptive accuracy and subjective ratings of visceral awareness. Indices of negative emotional experience correlated with interoceptive accuracy across subjects. These findings indicate that right anterior insula supports a representation of visceral responses accessible to awareness, providing a substrate for subjective feeling states. |
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