Each moment of consciousness is the result of intense competition between neuronal impulses from different facets of our mind. Some represent long term memories, objectives and desires, others the raw sensory input of the moment, and still more continuing to fire from the previous instant of consciousness. The thought, sensation or emotion potentiated is selected based on the frequency of its firing and the strength of its links with others that fired along with it. Neurones that fire for the abstract concept of a tree, for example, are more likely to fire off when preceded with the firing of linked ideas, such as forests or nature.
When the victor of this competition is pain, such as when we tread on a pin, that instant of consciousness will be dominated almost completely by a redirecting of awareness to the overriding stimulus: making us aware of the noxious stimuli, diverting our gaze to the source of the pain, and alerting us to the fact that we have instinctively pulled our foot away.
Furthermore, when we are prepared for incoming pain, when we’re about to be given an injection for example, our mind is primed to suppress the reflex withdrawal and even anger that would normally result from the sensory stimuli we are subjected to. In these cases, the higher cognitive levels of the frontal lobes, associated with planning, might become involved, interacting and modulating the more primal and reflex orientated aspects of our brain’s functions in preparation for the instants to come. We might even be able to continue a stream of dialogue with our friendly doctor; ensuring, through concentration and the suppression of other input, that the chain of neuronal firing responsible for producing logical sentences is not interrupted from one instant to the next.
This continuity is an essential feature of our conscious experience, with our more recently active (or generated) neuronal networks firing off with greater frequency than less relevant neurones, which might represent our mind’s map of our primary school, for example, or the visual stimuli of a long lost toy. Examples of this continuity in action would be the continual firing of a neurone representing the earlier content or gist of a friend’s tale as they expand into gory details, to recalling which seat at the dinner table is our own. This is known as ‘working memory’.
How are these networks generated? When I saw a firetruck for the first time in my wild and misspent toddlerhood, there is a good chance that it was driving along with neither the siren blaring nor the lights flashing, nor even indeed with any flaming building in sight. Now however, when I think of the word firetruck, my mind immediately leaps to such images, perhaps with some offshoots into subjectively related concepts such as firemen, the battery of my fire alarm, or even the bastards who set off midnight fire alarms at unholy hours in halls.
Prior to this first encounter I had probably developed a fairly extensive neuronal representation of what a firetruck might be associated with, having been a huge fan of ‘Fireman Sam’ as a child. If you had said the word ‘firetruck’ to me before I saw one in real life, the pre-existing neuronal network linked to the auditory stimuli of the word probably would have had a few synaptic connections with the word ‘Sam’ and the visual image of his stop motion figurine.
As the real life vehicle drove past me for the first time, the basic visual stimuli to enter my eyes would be of a large, red, rectangular version of a car, driving along a road. I would store this novel stimulus under the neurone labelled ‘firetruck’. For the first time, a raw sensory exposure to this object of interest to me would be recorded, with links made to the colour, size, noise, and vehicular nature of the firetruck.
Long-term memory is subject to the same principles. The human brain contains, at a conservative guess, around 86 billion neurones, each synapsing with an average of 7,000 others. When presented with the image of a fire truck, the raw data from the retina undergoes a great deal of processing before it enters the conscious field. There will be individual neurones that fire for almost every conceivable visual detail of an object. This pattern of firing would be preserved by one of the hallmark tenets of neuroscience – “neurones that fire together, wire together” – that is, a group of neurones that happen to be interconnected with most if not all of the stimuli, would strengthen their synaptic links with all of the lower echelon neurones, like the roots of a single bud.
The beauty of this system is that it allows each lower echelon neurone to fire off for many different objects, ideas or thoughts. A neurone that codes for circular shapes might fire off in response to anything from an apple to a clock, and would even fire off (though slightly less exuberantly) when presented with the raw sensory data for a pear, far more in any case than it would in response to a sock or a fire truck. It is by matching profiles of the firing (and indeed the specific frequency of firing) of many hundreds or thousands of neurones to a select few, higher echelon neurones, linked with others coding for verbal labelling and other associations, that we are able to so easily re-subject ourselves to past experiences, thoughts and sensations at will – the networking of the brain allows us to recall, at will, the image, sound, taste, emotional significance or functionality of an idea or object. This ability is intrinsically linked to perhaps the most significant difference between other animals and man – language.