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.