Figure 1.2. A cross section of the brain.
1 = brain stem, 2 = corpus callosum, 3 = cerebellum, 4 = white matter, 5 = grey matter, 6 = thalamus
If you examine the cerebral cortex you find it is in two areas. Inside the cortex is a white area, the white matter, wrapped around those central structures such as the limbic system and thalamus (and see figure 1.2). This white matter is simply billions of nerve fibres criss-crossing the system, connecting everything to everything else as we have already seen. On the outer edge of the cortex, though, is a grey zone, the grey matter, made up of neuron cell bodies, the ‘little grey cells’. If you placed a section of this grey matter under a microscope you would see that it is a layer about 110 cells thick, on average. You would see that these cells tend to be arranged in columns. Each column is thus an arrangement of about 110 cells in a line and it is thought that it probably functions as a unit which analyses a single detail of information. Each column of cells, perhaps, ‘thinks about’ – processes information about – a single detail. These columns of cells seem themselves to be arranged into microscopic modules, each module comprising many columns and each responsible, perhaps, for processing related information - thinking about a single subject. Let us use voice recognition as an example. We recognise people by voice alone, so there must be a ‘voice bank’ in there somewhere. Perhaps it is a module. Perhaps each column of cells in this module is responsible for monitoring incoming voices over a narrow range of frequencies, and a module of several such columns, each dealing with slightly different frequency ranges, will be able to ‘read out’ the frequency distributions of any voice heard. This could be said to be our phase one voice bank, our voice recognition phase one.
Remember, though, that every neuron may make thousands of connections with, and receive thousands of connections from, other cells, in other columns, nearby or far away. Some will connect with closely related columns in modules dealing with closely related information, but others will connect with distantly related columns in modules dealing with distantly related information or ideas. Remember, also, that some are excitatory ‘on switch’ connections while others are inhibitory ‘off switch’ connections. Remember also that I have only completed phase one of my voice recognition. I have a read-out of the frequencies, but no real-world meaning for this data. The frequency pattern data recognised in my voice bank in phase one must be interpreted, given meaning against the real world, in another association area - an area in which I may associate voice read-out data with personal ID. Here, I may associate (cross-reference) the frequency characteristics of voices with the identity of persons – I may recognise actual people by voice, in short. Exciting the neurons relating to a particular person in this area will, of course, tend to send impulses racing away down the neuron cell protrusions from their ID module and some of these will excite appropriate cells in the areas where physical data about people is held, and so a mental picture of the person may also be formed.