Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Concepts And Memories
Last but not least, the brain "categorizes".
The brain needs to categorize environmental stimuli that are valuable for survival. Every second we are bombarded with millions of sensory stimuli and we slowly force an organization on them, discarding some and retaining others. We turn a chaotic deluge of random stimuli into an ordered flow of patterns. We categorize them in "events", "situations" and "things". The newborn is simply powerless in the face of excess information. We learn slowly to process information and reduce its complexity by organizing our brain.
The brain understands what matters by reducing stimuli to concepts, categories. The brain remembers by linking new memories to old memories.
The brain, in the face of huge daily sensory stimulation, has a crucial task:
· understand what matters
· understand what does not matter
· remember what will still matter
· forget what will never matter again
Memories are stored in neural activity patterns which are distributed throughout the brain. This system of storage is more versatile and redundant than a "container". It is more redundant because a portion of the brain may be damaged without seriously affecting the overall pattern representing a memory. It is more versatile because it makes it easier to link many different memories.
Retrieving a specific memory does not entail finding its location, but turning on its pattern of neural activity.
The British zoologist John Young can be credited with starting (in 1964) "selectionist" thinking about the brain. He understood that learning could be the result of the elimination of neural connections (or, better, weakening of synapses).
In the 1950s Roger Sperry demonstrated that the brain is pre-wired by the genetic program to deal with some categories and to coordinate some movements. Sperry proved that experience is not enough to shape the brain, whereas Young proved that experience shapes the brain in a Darwinian manner.
The essential feature of the brain is that it is a dynamic system, capable of changing very quickly. Even the adult brain "grows".
Only about a quarter of the brain is already grown at birth. It is not only quantity, it is mainly quality that is missing. In fact, quantity is taken care of very rapidly: four weeks after conception, an embryo is creating neurons at the fantastic rate of about 500,000 per minute. Six weeks after conception (three months before being born), a fetus has actually more neurons than it will ever have. “Intelligence”, though, comes from the synapses.
At birth, the brain has fewer synapses than an adult brain. While the brain comes with some synapses pre-wired, many are formed in response to the environment. Synapses proliferate rapidly during the first two years of life. Virtually every event of a child's life leads to the creation of synapses. By far, it is the cortex that witnesses the highest frequency of synaptic creation, while the rest of the brain is largely unchanged after birth. At birth a human brain is much less “finished” than the brains of other animals.
Concurrent with the explosion of synapses is a rapid pruning away of those that do not get used. The brain is built through the interplay of genes and experience. The newborn brain comes equipped with a set of genetically based rules that specify how learning takes place. Then the brain is literally shaped by experience (by what is used and what is not used).
The infant's brain organizes itself under the influence of waves of "trophic" factors. Such factors are chemicals that promote the growth and interconnections of nerve cells. They are released in waves so that different regions of the brain become connected sequentially. Again, the process is modulated by experience (by what happens to the infant, i.e. by which stimuli enter the infant’s brain).
Besides the creation and deletion of synapses, the brain undergoes another phenomenon that shapes its ability to “think”: synapses change, again, in response to the environment. Synapses are not simple links between neurons, they are more or less effective in implementing such a link.
Donald Hebb's hypothesis, formulated in the late 1940s, is that the basis for neural development lies in a selective strengthening or inhibition of synapses. Synapses that get used are reinforced, while synapses that are not used are inhibited. This dual process molds the structure of the brain in a Darwinian fashion: the more “useful” synapses are the ones that survive. These synaptic changes are the basis for all learning and memory.
Hebb had already realized that metabolic change occurs in the brain all the time.
The selective strengthening of the synapses causes the brain to organize itself into “cell assemblies”, regions of interconnected self-reinforcing sub-nets of neurons that form for long periods of time. These acts of “reinforcing” are more than mere “stimulus-response” pairs: they are reverberating processes that occur over a network of cells. Each assembly represents a fragment of a concept. An assembly may overlap others, so that concepts are naturally linked into larger concepts. Each resonating cell assembly behaves like a rule: triggered by an event, it will fire for a while at a higher rate.
Psychological conditioning is ubiquitous in animals because it is a property of the elementary constituents of the brain.
Another of Hebb's great intuitions was the "phase sequence". A cell assembly facilitates the formation of another one, normally in conjunction with an external stimulus. A series of chained cell assemblies constitutes a "phase sequence", in which, basically, one thought leads to another.
The elementary constituent of “thought” is actually a population of interconnected neurons (a cell assembly) rather than the individual neuron.
The brain is an evolutionary system: genes determine only its initial configuration, whereas experience molds the brain according to Darwinian principles of selection.
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