EDELMAN'S NEURAL DARWINISM
Distinguished neuroscientist, Gerald Edelman shared the Nobel Prize for medicine in 1972 for his work on the structure of antibodies. In 1997 Edelman’s proposed that “the brain like the immune system, is a selection system that operates within an individual’s lifetime.” This powerful insight was elaborated “subsequently under the name Neural Darwinism.” Several decades, later in Second Nature (2006: 27-31), a small volume addressing the nature of consciousness for a non-specialist audience, Edelman rests his theory of neuronal group selection (TNGS) on several tenets:
…the development on neuronal circuits in the brain leads to enormous microscopic anatomical variation that is a result of a process of continual selection. A major driving force for this developmental selection is the fact that, even in the fetus, neurons that fire together wire together.
…an additional and overlapping set of selection events occurs when the repertoire of anatomical circuits that are formed receives signals because of an animal’s behavior or experience. This experiential selection occurs through changes in the strength of the synapses that already exist in the brain anatomy. Some synapses are strengthened and some are weakened.
“The net result of developmental and experiential selection is that some neural circuits are favored over others.” A critical feature that emerges from these tenets is that “each brain is necessarily unique in its anatomical structure and its dynamics”—even the brains of identical twins.
REENTRY AND DEGENERACY
The brain is speaking mostly to itself. Edelman (2006: 28): describes the staggeringly complex systems of intraconnections within the brain:
Reeentry is the continual signaling from one brain region (or map) to another and back again across massively parallel fibres (axons) that are known to be omnipresent in higher brains.
Edelman draws parallels with the genetic code which consists of 64 triplet combinations of messenger RNA bases that code for only 20 amino acids. For Edelman (2006: 33):
…brain circuits under selection must be degenerate. Degeneracy refers to situations in which different structures can yield the same output or consequence… like genetic code. .. It is an essential property of selectional systems.
Edelman notes that “degeneracy in brain circuits leads almost inevitably to association, a key property required for memory and learning.” Degeneracy and association imply degrees of freedom and a certain looseness of fit that help to explain the brain’s astonishing ability to spot pattern, interpret incomplete information and generate predictions.
Edelman champions (2004: 124) the reentrant brain’s ability to construct—from multiple overlapping perspectives—a singular “coherent picture at all costs”:
Filling in of the blind spot, the phenomena of apparent motion, and gestalt phenomena can all be explained in terms of temporal synchrony in reentrant circuits. The same is true of the sense of time, of succession and duration.
GERALD M. EDELMAN
American biologist and Nobel laureate; Founder and Director of the Neurosciences Institute in San Diego. [1929- ]
NOTHING LIKE A COMPUTER
Neural Darwinism (TNGS) dispels any notion that the brain operates by unambiguous logical rules. “One illusion” that Edelman (2006: 9) dispels “is the notion that our brains are computers and that consciousness could emerge from computation.” Brains are certainly not built like computers. Embryonic and fetal brain development is epigenetic, stochastic (statistically variuable) and degenerate. Edelman assures us (2004: 29-30) that:
This is no way to build a computer, which must execute input algorithms or effective procedures according to a precise prearranged program and with no error in wiring… what would be lethal noise for a computer is in fact critical for the operation of higher-order brain functions.
Given that brain function depends on the firing synapses, it is tempting to think of the fundamental units of the functioning brain as binary logic gates. Philosophers have speculated that the fundamental principles of logic (including the law of identity, the law of excluded middle and the law of contradiction) are, literally, laws of thought. Viewed this way, essentials of propositional logic such as “and,” “or ” and “not” are the stuff of stimulation threshold and inhibition of firing synapses in the brain. Edelman opposes and successfully refutes this conventional viewpoint. Furthermore, he rejects the need for “a specific language-acquisition device.”
From Edelman’s TNGS standpoint, pattern recognition, making generalizations and metaphor precede logic, rather than the reverse. Although not stated specifically, an inescapable conclusion is that induction is our primary mode of reason rather than deductive logic. For Edelman (2006: 9 and 2004: 135) logic becomes a powerful but secondary mode—emerging from and intrinsic to language—“that can then be employed to eliminate ambiguity.”
In certain circumstances, natural languages gain as much strength from ambiguity as they do under other circumstances through the power of logical definition. Association and metaphor are powerful accompaniments of conscious experience even at very early stages and they flower with linguistic experience.
Edelman points to the “adaptive value” of highly contextualized “discriminations” with “shifting fringes”:
What they lack in absolute precision, they make up for by enhancing our ability to generalize, to imagine and to communicate in a rich environment. Higher order consciousness may be considered as a trade-off of absolute precision for rich imaginative possibilities.
Edelman, Gerald M. (2004) Wider than the Sky: the Phenomenal Gift of Consciousness. Yale University Press, New Haven and London.
Edelman, Gerald M. (2006) Second Nature: Brain Science and Human Knowledge. Yale University Press, New Haven and London.
JEAN-PIERRE CHANGEUX
Eminent French Neuroscientist
[1936- ]
it incorporates, within a defined genetic envelope peculiar to the species, a series of nested “epigenetic” imprints that are established by variation and selection.
For Changeux “evolutionary (epigenetic) competition inside the brain takes over from the biological (genetic) evolution of the species,” creating “organic links” with the physical, social, and cultural environment. Changeux purports (2000: 239) that “the adult human brain” results from “at least four interlocking evolutions”; specifically:
1. “[E]volution of the species in paleontological time”
2. “Individual evolution, through the epigenesis of neural connections”
3. “Cultural evolution, likewise epigenetic but extracerebral”
4. “Evolution of personal thought, which occurs in psychological time”
A powerful implication here—championed also by Gerald Edelman (2004 and 2006)—is that philosophy, aesthetics, ethics and the other human sciences are not separated from the hard science by an epistemological chasm. Neuroscience and philosophy are not parallel, incommensurable discourses. The gap can be bridged by conceding that first-person subjective experience emerges from brain activity. Consciousness emerges because like lesser qualia (for example: the sensation of blueness) it is entailed, but not—in a reductionist sense—caused by neuronal activity. Changeux describes this bridging of the epistemological chasm as a “ very fruitful interface… produced in an entirely natural way… with the human sciences and society.”
Changeux, Jean-Pierre and Ricoeur, Paul (2000) What Makes Us Think? A Neuroscientist and a Philosopher Argue About Ethics, Human Nature and the Brain. Princeton University Press.
Edelman, Gerald M. (2004) Wider than the Sky: the Phenomenal Gift of Consciousness. Yale University Press, New Haven and London.
Edelman, Gerald M. (2006) Second Nature: Brain Science and Human Knowledge. Yale University Press, New Haven and London.