Most Helpful Customer Reviews
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5.0 out of 5 stars
Neurobiology of consciousness, 7 Oct 2009
This is an excellent review of consciousness from the neurobiological point of view. Consciousness has been an interesting topic for study not only for neurobiologists but also for philosophers and physicists. Although consciousness is a highly debated topic because of its close interaction with matter in space and time, it is certainly least understood subject as it is at the borderline of physics, philosophy and neurobiology. Some quantum physicists argue that it is a universal field like space, time or energy, but consciousness does not figure in equations or any mathematical calculations. Secondly consciousness is found only in living beings and not in inanimate objects: Particularly animals that have brain and central nervous system. The book is summarized as follows:
Three working assumptions are made as methodological platform; 1) the physics assumption; conventional physical processes are required to explain consciousness or the conscious experience, 2) the evolutionary assumption; consciousness is evolved by natural selection in the animal systems, and 3) qualia assumption; the subjective, qualitative aspects of consciousness, being private, cannot be communicated directly through a scientific theory. The authors do not attempt to explain many forms of perception, imagery, thought, emoŽtion, mood, attention, will, or self-consciousness. Instead, they concentrate on certain fundamental properties of consciousness that are shared by every conscious states, such as the unity of a conscious state experienced as a whole and cannot be subdivided into independent components, and the inforŽmativeness, i.e., where a conscious state is selected from a repertoire of billions of possible conscious states, each with different behavioral consequences within a fraction of a second. The basic assumption in all this is that consciousness is a process that is private, selective, and continually changing. It is strictly a process, and not belonging to a particular section of brain. This means that consciousness is associated with biological structures that produce dynamic processes. Thus both morphology and consciousness are the products of evolutionary selection (natural selection). This assumption about the evolutionary origin of consciousness avoids fruitless efforts to relate consciousness to computer logic or the effect of quantum gravity on neurons or a pure quantum physical process while diminishing the role of brain.
Neural substrates of consciousness involve large populations of neurons and no single area of brain is responsible for conscious experience. As the task to be learned is practiced and its performance becomes more and more mechanical then the learning task fades from the memory and the regions for this task becomes smaller. Conscious experience is associated with changes of activity patterns occurring simultaneously in many regions of brain (i.e., activation and inactivation of a population of neurons). It is not how many neurons are active but it is the distribution of groups of neurons that can engage in strong and rapid re-entrant interactions. Further more, the activity patterns of rapidly interacting groups must be constantly changing and sufficiently differentiated from each other: This is called Dynamic Core Hypothesis. Consciousness is an extraordinarily differentiated. At any given time, we experience a particular conscious state selected out of billions of possible states, each of which can lead to different behavioral consequences. The occurrence of a particular conscious state is therefore highly informative in the specific sense that information is the reduction of uncertainty among a number of alternatives. If this is the case the neural processes underlying the conscious experience must also be highly differentiated and informative.
Memory is a central brain mechanism that leads to consciousness. Memory does not store inscription or information in any format. In higher organisms it is an act of creation for every act of perception, and every act of memory is an act of imagination. The primary consciousness has the ability to construct an integrated mental scene in the present that does not require language or true sense of self. The integrated neural scene depends on both perceptual categorization of incoming sensor stimuli (the present) and its interaction with categorical memories (the past). The neural mechanisms distinguish primary consciousness and higher order consciousness. Primary consciousness is found in human as well as some higher order animals, but these lack language, analytical skill, and limited symbolic (semantic) capabilities. Still they are capable of constructing a mental scene. The higher-order consciousness found in humans has semantic capability and linguistic capability in most advanced form which provides a sense of self and the ability to construct past and future. The author' main contention is that the consciousness arose from evolutionary innovations in the morphology of the brain and body. The mind arises from the body and its development. Much of the discussion by the authors are theoretical in nature and needs extensive experimental evidences to support this theory.
1. The Creative Cosmos: Towards a Unified Science of Matter, Life and Mind
2. Languages of the Brain: Experimental Paradoxes and Principles of Neuropsychology (Prentice-Hall series in experimental psychology)
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5.0 out of 5 stars
Neural Darwinism reaches out to the mind., 5 Sep 2000
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 behaviours that one might act out, there is no room for a Humunculus (the little man inside the man 'seeing' solutions) 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 yrs. 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 routinised behaviour 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, co-ordinated behaviour (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 behavioural 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.
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by GM Edelman
by ER Kandel
by Antonio Damasio
