Editing Gerald Edelman (section)

==Theory of consciousness==
{{See also|Secondary consciousness}}

In his later career, Edelman was noted for his theory of [[consciousness]], documented in a trilogy of technical books and in several subsequent books written for a general audience, including ''Bright Air, Brilliant Fire'' (1992),<ref>{{cite journal|author=Tauber, Alfred I.|author-link=Alfred I. Tauber|title=Review of ''Bright Air, Brilliant Fire: On the matter of the mind'' by Gerald M. Edelman|date=November 19, 1992|journal=N Engl J Med|volume=327|issue=21|pages=1535–1536|doi=10.1056/NEJM199211193272119}}</ref><ref>{{cite journal|title=Review of ''Bright Air, Brilliant Fire: On the Matter of the Mind'' by Gerald Edelman|journal=Kirkus Reviews|date=April 20, 1992|url=https://www.kirkusreviews.com/book-reviews/gerald-m-edelman/bright-air-brilliant-fire/}}</ref> ''[[A Universe of Consciousness]]'' (2001, with [[Giulio Tononi]]), ''[[Wider than the Sky]]'' (2004) and ''Second Nature: Brain Science and Human Knowledge'' (2007).

In ''Second Nature'' Edelman defines human consciousness as:
: "... what you lose on entering a dreamless deep sleep ... deep anesthesia or coma ... what you regain after emerging from these states. [The] experience of a unitary scene composed variably of sensory responses ... memories ... situatedness ..."

The first of Edelman's technical books, ''The Mindful Brain'' (1978),<ref>{{cite book| title=The Mindful Brain: Cortical Organization and the Group-selective Theory of Higher Brain Function| author=Gerald M. Edelman| publisher=MIT Press |year=1978 |isbn=978-0-262-05020-3}}</ref> develops his theory of [[Neural Darwinism]], which is built around the idea of plasticity in the neural network in response to the environment. The second book, ''Topobiology'' (1988),<ref>{{cite book| title=Topobiology: An Introduction to Molecular Embryology| author=Gerald M. Edelman| publisher=Basic Books| year=1988| isbn=978-0-465-08634-4| url=https://archive.org/details/topobiologyintro00edel}}</ref> proposes a theory of how the original neuronal network of a newborn's [[brain]] is established during development of the [[embryo]]. ''The Remembered Present'' (1990)<ref>{{cite book| title=The Remembered Present: A Biological Theory of Consciousness| url=https://archive.org/details/rememberedpresen0000edel| url-access=registration| author=Gerald M. Edelman| publisher=Basic Books| year=1989| isbn=978-0-465-06910-1}}</ref> contains an extended exposition of his theory of [[consciousness]].

In his books, Edelman proposed a biological theory of consciousness, based on his studies of the immune system. He explicitly roots his theory within [[Charles Darwin]]'s Theory of [[Natural Selection]], citing the key tenets of Darwin's population theory, which postulates that individual variation within species provides the basis for the natural selection that eventually leads to the evolution of new species.<ref>{{cite book |author=Gerald M. Edelman |author2=Jean-Pierre Changeux |title=The Brain |publisher=Transaction Publishers| year=2001 |page=45}}</ref> He explicitly rejected [[Dualism (philosophy of mind)|dualism]] and also dismissed newer hypotheses such as the so-called [[computational theory of mind|'computational' model of consciousness]], which liken the brain's functions to the operations of a computer. Edelman argued that mind and consciousness are purely biological phenomena, arising from complex cellular processes within the brain, and that the development of consciousness and intelligence can be explained by Darwinian theory.

Edelman's theory seeks to explain consciousness in terms of the morphology of the brain. A brain comprises a massive population of neurons (approx. 100 [[billion]] cells) each with an enormous number of synaptic connections to other neurons. During development, the subset of connections that survive the initial phases of growth and development will make approximately 100 [[trillion (short scale)|trillion]] connections with each other. A sample of brain tissue the size of a match head contains about a billion connections, and if we consider how these neuronal connections might be variously combined, the number of possible permutations becomes hyper-astronomical – in the order of ten followed by millions of zeros.<ref>{{cite book |author=Gerald Edelman |title=Bright Air, Brilliant Fire |publisher=Penguin |year=1992 |page=17}}</ref> The young brain contains many more neural connections than will ultimately survive to maturity, and Edelman argued that this redundant capacity is needed because neurons are the only cells in the body that cannot be renewed and because only those networks best adapted to their ultimate purpose will be selected as they organize into neuronal groups.

===Neural Darwinism===
Edelman's theory of neuronal group selection, also known as '[[Neural Darwinism]]', has three basic tenets—Developmental Selection, Experiential Selection and Reentry.
# '''Developmental selection''' -- the formation of the gross anatomy of the brain is controlled by genetic factors, but in any individual the connectivity between neurons at the synaptic level and their organisation into functional neuronal groups is determined by somatic selection during growth and development. This process generates tremendous variability in the neural circuitry—like the [[fingerprint]] or the [[Iris (anatomy)|iris]], no two people will have precisely the same synaptic structures in any comparable area of brain tissue. Their high degree of functional plasticity and the extraordinary density of their interconnections enables neuronal groups to self-organise into many complex and adaptable "modules."  These are made up of many different types of neurons which are typically more closely and densely connected to each other than they are to neurons in other groups.
# '''Experiential selection''' -- Overlapping the initial growth and development of the brain, and extending throughout an individual's life, a continuous process of synaptic selection occurs within the diverse repertoires of neuronal groups. This process may strengthen or weaken the connections between groups of neurons and it is constrained by value signals that arise from the activity of the ascending systems of the brain, which are continually modified by successful output. Experiential selection generates dynamic systems that can 'map' complex spatio-temporal events from the sensory organs, body systems and other neuronal groups in the brain onto other selected neuronal groups. Edelman argues that this dynamic selective process is directly analogous to the processes of selection that act on populations of individuals in species, and he also points out that this functional plasticity is imperative, since not even the vast coding capability of entire human genome is sufficient to explicitly specify the astronomically complex synaptic structures of the developing brain.<ref>Gerald Edelman, ''Bright Air, Brilliant Fire'' (Penguin, 1992), p.224</ref>
# '''Reentry''' {{Main|Reentry (neural circuitry)}}—the concept of reentrant signalling between neuronal groups. He defines reentry as the ongoing recursive dynamic interchange of signals that occurs in parallel between brain maps, and which continuously interrelates these maps to each other in time and space ([http://www.acamedia.info/movs/edelman/reentrant_signaling.flv film clip]: Edelman demonstrates spontaneous group formation among neurons with re-entrant connections).<ref>Gerald Edelman: "[http://video.google.com/videoplay?docid=7437432153763631391 From Brain Dynamics to Consciousness: A Prelude to the Future of Brain-Based Devices] {{Webarchive|url=https://web.archive.org/web/20120106110348/http://video.google.com/videoplay?docid=7437432153763631391|date=January 6, 2012}}", Video, IBM Lecture on Cognitive Computing, June 2006</ref> Reentry depends for its operations on the intricate networks of massively parallel reciprocal connections within and between neuronal groups, which arise through the processes of developmental and experiential selection outlined above. Edelman describes reentry as "a form of ongoing higher-order selection ... that appears to be unique to animal brains" and that "there is no other object in the known universe so completely distinguished by reentrant circuitry as the human brain."