viernes, 18 de noviembre de 2011

A Universe of Consciousness

Review - A Universe of Consciousness
How Matter Becomes Imagination
by Gerald M. Edelman & Giulio Tononi
Basic Books, 2000
Review by Anthony Dickinson, Ph.D.
Sep 9th 2000 (Volume 4, Issue 36)

This new volume provides a biologically-based perspective on consciousness. Although Edelman & Tononi may often appear to lead the reader into believing that a selector' is needed in order for one to choose between the many alternative possible kinds of behavior that one might act out, there is no room for a homunculus (the little controller inside the person) of any sort here. For those unfamiliar with Edelman's previous writings (all of which I would recommend) there are plenty quotes from his earlier self, the principle idea here being a logical extension of his thesis developed over the last 20 years.

Coming clean right from the start, the data acquired from introspection is rejected as a technique to be subjected to any robust empirical analysis, but consciousness is here identified not solely with brain states/activity (there is a clear need for interactions with others and the world out there) - the authors putting forward a model of consciousness as being a particular kind of brain process; unified/integrated, yet complex/differentiated.

The early parts of the book discuss the impasse' reached by many philosophers in their attempts to explain the mind-body' problem whilst rejecting both strong dualist and reductionist positions: "..consciousness requires the activity of specific neuronal substrates … but is itself a process, not an object". There is a clear appeal to holistic thinking here (the whole is greater than the sum of its parts') - but the message is more subtle. What Edelman & Tononi are pointing out is that, still in need of explanation is the fact that although the contents of consciousness change continually, its possessor remains continuous. The problem of how one discriminates between our vast repertoire of conscious states (and how one is selected' for experience in real time from this pool) is the main evolutionary question being addressed. Assumptions are not ignored (reflexes are allowed to operate in certain circumstances), but emphasis is placed upon the integration function of the human brain, rather than the clearly identified anatomical segregations long known to exist. For example, there have been at least 36 different visual areas reported in primate brain, each linked by more than 300 connection/projection pathways, 80% of which have recurrent-colateral or re-entrant connections. These latter findings are the focus of Edelman's developing theory of consciousness. For a long time now, many researchers have come to believe that distinct, distributed patterns of neuronal firing give rise to the integration of perceptual and motor processes - but how such patterns are strengthened to provide routinized behavior and expertise remains unclear. The data presented with respect to the detailed nerve receptor-level changes re growth and the known pharmacological effects of certain natural transmitter substances and drugs are welcome and well written for the lay person to follow (often lacking in the specialist journals of the field!). However this debate may resolve, Edelman & Tononi are here suggesting that in like process, coordinated behavior (including consciousness) derive from the detailed brain connectivities together with their variability and plasticity over time - especially in relation to the (highly flexible?) dynamics of reentrant connections. How such distributed neuronal firing patterns are selected for as the brain interacts with the body' requires better evidence, but with our current state of knowledge, this is definitely a step in the right direction.

From an evolutionary perspective, this is Neural Darwinism writ large, proposing a research agenda entirely consistent with that thesis. For those in the know, there are also (uncited) tributes to Waddington (as in Epigenetic Landscapes) and support for those working on behavioral robotics and the emergent properties of dynamic systems. The details of the text I will leave to the reader to enjoy - clinical data, normal and abnormal brain architecture, even systems theory - all accessible and clearly phrased for the non-expert reader. As with his previous writings in evolutionary neuroscience his work feels right and if successful (and hope that they are) Edelman could follow in the footsteps of Marie Curie in claiming a second Nobel Prize.

Dr. A. R. Dickinson, Dept. of Anatomy & Neurobiology, Washington University School of Medicine

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