Edelman’s Brain-Based Theory of Consciousness

Gerald Edelman, American biologist and 1972 Nobel Prize winner, offers a biological theory of consciousness founded on Darwin’s Theory of Natural Selection. His most recent book, Second Nature: Brain Science and Human Knowledge, outlines the key tenets of his theory of consciousness developed throughout his career. In Edelman’s theory of Neural Darwinism, he describes three components of his neuronal group selection. First, he explains that “the development of neuronal circuits in the brain leads to enormous microscopic anatomical variation that is a result of a process of continual selection” (Edelman, 2006, p. 27). He refers to this as developmental selection and explains “the high degree of functional plasticity and the extraordinary density of their [neurons] interconnections enables neuronal groups to self-organize into many complex and adaptable modules” (Edelman, 2006). This idea is consistent with Hawkins, Dennett and Minsky, as well as, systems theory in general.

Edelman then describes experiential selection which he defines as the continuous process of synaptic selection that occurs within the diverse repertoires of neuronal groups throughout the development of the brain. He explains that “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, 2007). Edelman views this dynamic selective process as working analogously to the processes of selection that act on populations of individuals which leads to the name of his theory Neural Darwinism. This is based off of Darwin’s fundamental idea of population thinking in which variation in a population provides the basis for selection and survival.

Edelman’s third tenet, perhaps the most important in understanding higher capacities of the brain, is the concept of reentrant signaling between neuronal groups. Edelman (2007) demonstrates that there is a “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.” This reentrant circuitry appears to be unique to animal brains and he describes, “there is no other object in the known universe so completely distinguished by reentrant circuitry as the human brain” (Edelman, 2001, p. 44). Reentry is seen within the neuroanatomy of the brain as a dense meshwork of reciprocal connectivity among different cortical areas as well as between the cortex and the thalamus (Edelman, 2006). Hawkins (2006) explored these pathways and explains that in the circuitry between the neocortex and the thalamus, “the connections going backward (toward the input) exceed the connections going forward by almost a factor of ten” (p.25). This reentrant circuitry allows humans to link numerous sensory signals together, make perceptual categorization and then connect them in various combinations to memory (Edelman, 2006).

This reentrant system in influenced by value systems and by selected synaptic changes by previous experiences. Edelman (2006) explains that “from very early developmental times, signals from the body to the brain and from the brain to itself lay the grounds for the emergence of a self” (p.37). Similar to Hawkins’ idea of auto-associative memories, conscious experience relies on references to its own memories. Additionally, conscious experience enhances communication with other individuals and is deeply rooted with language. Edelman proposes that at some point in high primate evolution, “a new set of reciprocal pathways was developed” which made “reentrant connections between conceptual maps of the brain and those areas capable of symbolic or semantic reference” (p. 38). According to Neural Darwinism, this reentry in the enormously complex dynamic core was the “key integrative event that led to the emergence of conscious experience” (p. 39). The feedback and messages the brain sends to itself which is often ignored in studies of intelligence may be the decisive factor to understand human experience.