Gerald M.Edelmann A UNIVERSE OF CONSCIOUSNESS Basic 2000

pg 111 The Dynamic Core Hypothesis At the beginning of this book, we proposed that a scientific analysis of consciousness should account for the fundamental properties of conscious experience—those shared by every conscious state. Among such fundamental properties are the following two: first, consciousness is highly integrated or unified—every conscious state constitutes a unified whole that cannot effectively be subdivided into independent components— and second, at the same time, it is highly differentiated or informative—there is an enormous number of different conscious states, each of which can lead to different behavioral consequences. As we have already seen, the distributed neural processes underlying conscious experience also share these properties: They are highly integrated and, at tbe same time, highly differentiated. We believe that this convergence between neurobiology and phenomenology is not mere coincidence. On the contrary, it can yield valuable insights into the kinds of neural processes that can account for the corresponding properties of conscious experience. In this part of the book, we attempt to account for the unity and informativeness of conscious experience and further develop our ideas on the neural bases of conscious experience by providing a solid theoretical framework for the notions of integration and differentiation. First, we have to be clear about what we mean by integration and differentiation. Then we need to deal in a more precise fashion with how integration and differentiation are actually realized in the brain. We develop a quantitative measure of the functional clustering of neural activity, which is related to integration, as well as a quantitative measure of neural complexity, which is related to differentiation. Dealing clearly with these issues calls for some mathematics, although most of the technical aspects can be conveniently ignored as long as the concepts remain. The results of these analyses allow us to propose a hypothesis, called the dynamic core hypothesis, which provides a concise operational statement of what is special about the activity of groups of neurons that underlies conscious experience. On the basis of the dynamic core hypothesis, we revisit the key properties of consciousness that we described before and provide a set of clear-cut empirical criteria for distinguishing the neural processes that contribute to consciousness from those that do not. Integration and Reentry In this chapter we intend to achieve a more complete srientific understanding of the neural processes that explain the unity or integration of conscious exterience. Toward this end, we define precisely what we mean by integration, how integration can be measured, and how an integrated neural process can be identified. We do so by introducing a new concept: the "functional cluster". We also discuss the means by which the integration or binding of the activity of distributed brain areas can be brought about in less than a second. This is a famous problem in today's neuroscience - often called the "binding problem". Using the results of large-scale computer simulations, we show that reentry is the key neural mechanism hy which integration can be achieved within the thalamocortical ystem and indicate how such integration can lead to a unified behavioral output. These results provide a parsimonious solution to the binding prohlem.

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