Neural Darwinism

There is now ample evidence^[for the active, experience-dependent re-organization of the synaptic networks of the brain involving multiple inter-related structures including the cerebral cortex. 

The specific details of how this process occurs at the molecular and ultrastructural levels are topics of active neuroscience research. The way experience can influence the synaptic organization of the brain is also the basis for a number of theories of brain function including the general theory of mind and epistemology referred to as Neural Darwinism. 

 Gerald Edelman's theories are rooted in neurology. In fact, he insists that this is the only foundation for a successful theory of consciousness: the answers are not to be found in quantum physics, philosophical speculation, or computer programming.

The structure of the brain is accordingly a key factor. The neurons in the brain wire themselves up in complex and idiosyncratic patterns patterns during growth and then experience: no two people are wired the same way. 

The neurons do come to compose a number of structures, however. They form groups which tend to fire together, and for Edelman these groups are the basic operating unit of the brain. 

The other main structures are maps. An uncontroversial example here might be the way some sheets of neurons reproduce the pattern of activity on the retina at the back of the eye (with some stretching and squashing), but Edelman sees similar strucures as applying much more widely, and mapping not just sensory inputs, but each other and other kinds of neuronal activity. The whole system is bound together by re-entrant connections, sets of paths which provide parallel connections from group A to Group B and Group B back to Group A.

The principle which makes this structure work is Neuronal Group Selection, or Neural Darwinism. Some patterns are reinforced by experience, while many others are eliminated in a selective process which resembles evolution. Edelman draws an analogy with the immune system, which produces a huge variety of random antibodies: those which link successfully to a foreign substance reproduce rapidly. This explains how the body can quickly produce antibodies for substances it has never encountered before (and indeed for substances which never existed in the previous history of the planet): and in an analogous way the Theory of Neuronal Group Selection (TNGS) explains how the brain can recognise objects in the world without having a huge inherited catalogue of patterns, and without an homunculus to do the recognising for it.  

The re-entrant connections between neuronal groups in different parts of the brain co-ordinate impressions from the different senses to provide a coherent, consistent, continuous experience; but re-entry is also the basic mechanism of recategorisation,

 the fundamental process by which the brain carves up the world into different things and recognises those it has encountered before. The word recategorisation is potentially confusing here for two reasons: first, it is not to be taken as implying the existence of a prior set of categories: in fact, every act of recognition modifies the category; nor is it meant to suggest any parallel with Kant's categories, which limit how we can understand the world. Very much the reverse, in fact.

Edelman attaches great importance to higher-order processes - concepts are maps of maps, and arise from the brain's recategorising its own activity. Concepts by themselves only constitute primary (first-order) consciousness: human consciousness also features secondary consciousness (concepts about concepts), language, and a concept of the self, all built on the foundation of first-order concepts. 

The final key idea in the theory, another one with a slightly misleading name isvalue, a word used here to describe inbuilt tendencies towards particular behaviour. These forms of behaviour may be driven by what we value in a fairly straightforward sense - seeking food, for example, but they also include such inherent actions as the hand's natural tendency to grasp. Edelman seems to think that, like a computer, if left to itself the brain might sit and do nothing. It's the value systems which supply the basic drives. This sort of set-up has been modelled in a series of robots rather cheekily named Darwin I to IV.

Edelman is emphatically opposed to the id