The basic layout of our nervous system is well known. Just about every part of our body is supplied with nerves. These either gather information for, or deliver instructions from, the brain at the top of the system. Inside the brain itself nerves connect copiously between different areas of it and pass impulses back and to within the brain. Nerve cells, or neurons, are what make up the system. A nerve cell has a body and from this body there arise numerous, and sometimes extremely long, protrusions. All nerve fibres, or nerves, are just such protrusions, or collections of such protrusions, of neuron cell bodies. It is these fibres which carry nervous impulses around the system. They are the system’s wiring. Nerve fibres within the brain usually end in connections with other neurons. These are very numerous. Every neuron in the brain makes hundreds, often thousands, of connections with other neurons in the brain. Every neuron in the brain receives hundreds, often thousands, of such connections from other neurons in the brain. The many connections each neuron makes or receives may be with, or from, neurons close by or far away across the brain.
Since there are perhaps ten billion neurons in the cerebral cortex, each making perhaps a couple of thousand connections with other neurons, you can see that some deeply elaborate, even rococo, circuitry can be built, and built in vast amount too. (Actually, the number of neurons in your cerebral cortex, and the number of connections each may make, appear to vary according to the book you are reading at the time. I have just read a book telling me that there are a hundred billion neurons up there and that each may make ten thousand connections or more. Oh well …!) The point I am making is simply that, for practical purposes at any rate, your brain may be considered to be limitless in capacity. We should not be astonished by the man who speaks six languages; we should rather be surprised that we don’t all do this. Einstein’s brain (wherever it has got to) was very similar, physically, to yours or mine.
Some writers claim astounding things:
In the human cortex there is an awesome number of neurons, approximately ten billion. But the astonishing figure is the number of connections in the cortex, about one million billion. To count one of these connections each second would take thirty two million years. Even more stunning than the number of connections is the way the connections can be combined. The number of combinations that can be formed from the number of connections in the cortex is many times greater than the number of positively charged particles in the known universe, a number so great that we cannot give it a meaningful name. (Greenfield 1995 pp. 83-84)
Not only are connections between neurons numerous (to put it mildly), they can also be excitatory or inhibitory. An excitatory connection makes it much easier for a stimulus to pass; an inhibitory connection makes it more difficult. In other words the system can make ‘on’, ‘off’ and ‘dimmer’ switch connections. The vast number of interconnections arising from, and impinging upon, every neuron in the brain and the fact that some of these are ‘on’, some ‘off’ and some variable ‘dimmer’ switches are two salient points about the wiring of the brain for our present purposes. Another is the staggering interconnectedness of the thing – everywhere seems to be connected to everywhere else, one way or another. Your brain is bogglingly enormous; an astoundingly massive organ. We were impressed by the pace, amount and quality of work it performed on the tennis court back there but we should no longer be flabbergasted. We have huge capacity and, because it is all so interconnected, we also have the ability to perform a multitude of tasks simultaneously. Indeed, we do this all the time, as a moment’s reflection will show. With the hardware we have at our disposal this is easy enough.
Now we need a brief overview of the basic anatomy of the brain, some fundamental and applied neuroanatomy.
We can think of our brain as in four main functional parts: the brainstem/midbrain complex, the forebrain, the cerebellum and the cerebral cortex. (Damasio 2000 and England and Wakeley 1991). The brainstem/midbrain complex (and it is complex) comprises ancient, relatively primitive structures which need not, as they say, detain us long. Perhaps, when we understand better how this complex fits with, and perhaps intimately influences, the ‘higher’ structures of our brains this last remark will seem flippant but in our present state of knowledge, and for our present purposes, we can content ourselves with saying that the midbrain/brainstem complex is a complicated interconnecting and switching system which sorts incoming information from the body and outgoing instruction to the body. It monitor’s the body’s major systems and coordinates most unconscious activity. It keeps us alive and physiologically controlled but it doesn’t do any thinking, or have any fun. We will consider it no further in this book.