Gerald M.Edelmann
A UNIVERSE OF CONSCIOUSNESS
Basic 2000
The Special Problem of Consciousness .
....to identify and characterize not just the neurons but the neural processes that can account for key properties of conscious experience.
Science has always tried to eliminate the subjective from its description of the world. But what if subjectivity itself is its subject? In this chapter, we first explore the special status of consciousness and the assumptions necessary to study it from a scientific point of view.
We then examine a fundamental problem posed by the existence of consciousness - one that needs to be explained by any scientific account. Consider this simple example: Why is it that when each of us performs certain discriminations, such as between light and dark, each of us is conscious, but a similar discrimination performed by a simple physical device is apparently not associated with conscious experience?
This paradox suggests that attempts to understand consciousness that rely on the intrinsic properties of certain neurons or certain areas of the brain are doomed to failure. Next, we discuss the kinds of new approaches required if the bases of consciousness are to be understood. Finally, we delineate our strategy - to identify and characterize not just the neurons but the neural processes that can account for key properties of conscious experience.
pg. 20
Everyman's Private Theater:
Ongoing Unity, Endless Variety
Our strategy for explaining the neural basis of consciousness is to focus on the properties of conscious experience that are the most general, that is, that are shared by every conscious state. One of the most important of these properties is integration or unity. Integration refers to the fact that a conscious state cannot be subdivided at any one time into independent components by its experiencer. This property is related to our inability consciously to do more than two things at once, such as adding up a check while carrying on a heated argument.
Another key, and apparently contrastive, property of conscious exterience is its extraordinary differentiation or informativeness: At any moment, one out of billions of possible conscious states can be selected in a fraction of a second. We thus have the apparent paradox that unity embeds complexity the brain must deal with plethora without losing its unity or coherence. Our task is to show how it does so.
pg 37
Consciousness and the Brain
To understand consciousness as a process, we must understand how the brain works; we must know about its architecture, its development, and its dynamic functions.
This chapter presents a usable but by no means exhaustive picture of the brain, highlighting the brain's most important features: its anatomical organization and the remarkable dynamics that it generates. Although it is painted with a broad brush, this picture is necessary for understanding how consciousness emerges.
pg 51
Consciousness And Distributed Neural Activity
In this and the next chapter, we organise a wealth of old and new information on the relationship between neural activity and conscious states in health and disease. Our main goal is to highlight the overall characteristics of the neural processes underlying conscious experience. We touch on various observations, ranging from neurophysiology to neuropsychology, all of which provide fundamental evidence for how consciousness arises. We point out that the neural substrate of consciousness involves large populations of neurons - especially those of the thalamocortical system - that are widely distributed in the brain. Conversely, no single area of the brain is responsible for conscious experience. We also show that as a task to be learned is practised, its performance becomes more and more automatic; as this occurs and it fades from consciousness, the number of brain regions involved in performing a task becomes smaller.
pg 74
....empirical observations suggest that underlying consciousness are distributed neural processes that, through reentrant interactions, are at once highly integrated but continually changing and thus are highly differentiated. This conclusion becomes particularly relevant when one realizes that integration and differentiation are also general properties of conscious experience, irrespective of its specific content.
To understand how these phenomenological properties relate to the actual neural mechanisms that are responsible for consciousness cannot be just a matter of accumulating additional facts. It requires a robust theory - one that provides insights into the biological origins of pattern formation, perceptual categorization, memory, concepts, and values.
What kind of brain theory is compatible with the distributed, integrated, but continnously changing patterns of neural activity that can give rise to the unitary yet immensely differentiated phenomenology of conscious experience?
pg 77
Neural Darwinism
In his theory of natural selection, Charles Darwin provided the chief foundation of modern biology. After his return from the voyage of the Beagle, he made continuing efforts to understand how the functions performed by the brain arose during evolution. His notebooks reveal his struggle to explain how perception, memory, and language could have arisen by what he called descent.
We now have a rich evolutionary theory graced by the Darwinian perspective, but the problem of understanding mental processes is still with us. It remains for neuroscience to complete Darwin's program. In this part, we show how Darwinian principles embedded in a theory of brain function provide insights into the processes of perception, memory, and the assignment of value, all of which are critical to an understanding of consciousness. Once the reader grasps the nature of such processes, the stage will be set to consider the actual neural mechanisms by which consciousness arises during evolution and development. Our efforts here are focussed on consciousness, the ability to construct an integrated mental scene in the present that does not require language or a true sense of self.
We believe that this integrated mental scene depends not only on the perceptual categorization of incoming sensory stimuli - the present - but, most important, on their interaction with categorical memories - the past. In other words, this integrated mental scene is a "remembered present."
pg 79
The theory of neuronal group selection, or Neural Darwinism
In considering the origin of species, Charles Darwin made a great contribution that centered on population thinking: the idea that variation or diversity among individuals in a population provides a basis for competition during natural selection. Natural selection is reflected in the differential reproduction of fitter individuals in a species. In principle, selective events require the continual generation of diversity in repertoires of individual variants, the polling by environmental signals of these diverse repertoires, and the differential amplifcation or reproduction of those repertoire elements or individuals that match such signals better than their competition.
Could it be that the brain follows such principles? We believe it does, and in this chapter we briefly review some aspects of the theory of Neural Darwinism. This theory embraces these selective principles and applies them to the functioning brain. Its main tenets are
(1) the formation during brain development of a primary repertoire of highly variant neuronal groups tbat contribute to neuroanatomy (developmental selection),
(2) the formation during experience of a secondary repertoire of facilitated neural circuits as a result of changes in the strength of connections or synapses (experiential selection), and
(3) a process of reentrant signaling along reciprocal connections between and among distributed neuronal groups to assure the spatiotemporal correlation of selected neural events
Together, the three tenets of this global brain theory provide a powerful means for understanding the key neural interactions that contribute to consciousness.
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