5.6 Concentric organisation of the NAD; rigidity and plasticity.
Like the lymphoid system the nervous, or neuronal, system has evolved to carry out the following functions:
designing an internal map of the environment and of the self in relation to it,
storing an internal map of motor interactions with the environment (skills),
developing a value system regarding relevant aspects of the environment.
It is formed on the basis of emotional and sensorimotor experiences. To this end it has developed two different memory-tracks i.e. [1] the capacity for rapid attentional integration (short time memory), and [2] a buffer storage capacity (long term memory, Blumenthal 1977).
Map 5.6.1: The neural system for adaptation and defence
As in the map of the lymphoid system (5.2.3) we recognise in the NAD (Map 5.6.1) a concentrical arrangement of functions and behaviours: vital regulatory functions are close to the centre of the sphere, the more differentiated functions, such as voluntary behaviour and social skills, closer to the surface. The functions near the centre are rather rigid and hardly influenced by learning, closer to the periphery there is increasing plasticity. Most functions and behaviours are learned at an early age. As a consequence, the "behavioural style" with which an individual proceeds through life, has been formed in the first years of it's existence.
Most forms of behaviour are acquired by learning. But heredity determines the potential of an individual and sets limits to what it will be able to learn ('nature'). The kind of education ('nurture') as well as decisive incidents in the life history determine how much of the potential allowed by nature will be actualised. During childhood the environment selectively reinforces those elements from the developmental potential that fit the requirements of the moment. This is often a short-sighted strategy which may turn out to be maladaptive in the long run. Normally maladaptive behaviour will be replaced, before adulthood is reached, on the strength of more and better information and larger aims.
As long as it is alive the brain is engaged in 'adaptive learning': new connections between neurons are made, old ones are replaced. The neurons and their adjacent glia (supporting cells) constitute functional units. Their main business is combining or isolating streams of information. Combining takes place at the surface of cell-bodies and dendrites, the isolated transport takes place in the axones, that are part of the neuron cell and can extend from the spine to a toe. By changing its network properties, in interaction with the environment, the neural system is continuously improving its efficiency. Some parts of the brain are more flexible than others in this respect. Most flexible are those parts that have been acquired late in the phylogeny of man: the neocortex of both hemispheres or neo-encephalon. It surrounds the older parts of the brain: the paleo-cephalon and the spino-medullary part of the central nervous system.
- The 'hard' core of the brain is the substrate for innate reflexes that are resistant to modification by experience. It is immediately related to the internal maintenance of water-balance, blood-sugar levels etc.
- The midbrain together with the limbic system ('paleocortex') provide the substrate for the regularly recurring activities, concerned with alimentation and reproduction. When the demands on the physiologic systems exceed their capacity for control, supplementary behaviour maintains body-temperature, sustains water- and food intake. Closely related are appetitive and avoidance behaviours, sexual, fight, flight and withdrawal activities. Such emergency behaviours are called 'agonistic', they secure the integrity of the individual in extreme circumstances. In so doing they may interfere at unexpected moments with already acquired more sophisticated behaviour. This fact will prove to be of considerable interest for explaining otherwise inexplicable human communication disorders (Chapter 10). Although they are instinctive and inborn, their mode of execution is nevertheless largely modifiable by experience. The limbic system is considered to be the matrix for emotional and motivational learning. Early 'agonistic' survival strategies (neuroses) are stored here.
Farther away from regulatory processes we find a layer of skilled escape and avoidance behaviours, exploration and manipulation. They serve to improve the circumstances under which the individual tries to keep his physiological and emotional balance. Far removed from the physiologic homeostatic drives are the varied and voluntary behaviours. They are only loosely connected to the physiologic core functions and show a less stereotyped pattern than those more closely related to the physiological needs.
Regulatory behaviours are controlled by strictly defined substrates in and around the hypothalamus. The location of motivation for more voluntary behaviour, however, is not so strictly defined. We have an idea of how selecting an appropriate response works in a given instance. When a complex stimulus is received, it is rapidly scanned for cues that stand out because of their 'attention-value'. These are either general markers that are valid for all members of the species, or individual markers for which a person has been sensitized in particular. Incoming messages are then analysed in more detail on a higher level of the central nervous system, in the neo-encephalic part of the brain's cortex, where variable adaptive behaviours are organised. Variation in behaviour is wide, although always limited by the genetic potential of the individual. Within this limit, a selection from a large repertoire is made in response to immediate needs. Plasticity of the neo-encephalon allows the development of speech and language skills, in interaction with the environment. This is so in most humans, in some instances a genetic defect (e.g. a chromosomal aberration) or brain damage at birth limits the degree in which development of adaptation and adequate defence are possible.
From the foregoing we conclude that here is a sequence through which the genetic information passes in order to be expressed in one of the functional layers:
(physiological) regulatory functions
drives, primary motivation
involuntary functions and behaviour
supplementary behaviour
voluntary behaviour controlled by secondary motivations.
Physiological functions (deep structures) and voluntary behaviour (surface structures) supplement each other. An every-day example will illustrate this. When you are working in the sun, your autonomic system adapts to the situation by increasing the blood circulation to the body's surface and by sweating. When the need for heat-loss surpasses the capacity of your physiological regulation system, voluntary action will supplement it. By taking off coat and shirt or by taking a rest in the shade you carry out an imperative dictated by your physiology. It is easy to think of other examples of seemingly voluntary behaviour, that stem primarily from physiological drives: having breakfast, drinking a glass of water, going to sleep etc.
Cognitive processing not only serves to immediately carry out behaviour inspired by drive-motivated needs, it also anticipates physiological needs before they become too demanding. It is also inherent in humankind to freely play around with cognitive agility. As human beings we can conjure up possible and impossible worlds just by thinking. Language is a very suitable instrument for this creative activity, by which we try plan actions for ourselves and communicate about them with other people.
With our immune system we create an internal image of the material world in which we live so we can anticipate its challenges. As the syntax and grammar of the lymphoid network reveal themselves to the experts in the field, they begin to see a chemical symbol-system, governed by grammatical rules, which scans the environment for antigens. The neural system goes one step further. With our neural adaptation/defence system (NAD) we create an internal image of the world in which we live, as we have perceived it through our senses. Spoken and written language have added to this memory bank: a large part of the perception and interpretation of our environment has come to us by means of oral and written verbal information. Since the 1930's the movement of General Semantics has been studying the many ways in which we perceive, interpret, misconceive and misinterpret the world in which we live.
Speech and language are a phylogenetically young, verbal system for adaptation and defence (VAD). Analogies with man's other systems for adaptation and defence make it very probable that the organisation of language within the neuronal system is a concentrical one. As in the case of the immune and the neural systems the VAD has a firm, genetically based core, which by differentiation has generated pliable surface structures (Chapter 7).