8.1 Structure of the brain and levels of the mind. Zones of adaptation and
Structure of the brain and levels of the mind. Zones of adaptation and defence.
Medicine as well as education can profit greatly from the germ-layer classification of body and behaviour (Chapter 7). The model is in agreement with the Maps of growth, development and learning which we have been discussing in previous chapters. This adds a measure of mutual validation to the proposed concentric models.
We have come upon palpable examples of concentrically arranged functions. In cross-sections of a developing embryo the concentric arrangement of the embryonic layers is evident. Equally suggestive of a concentric building plan is the arrangement of the full-grown brain. According to Yakovlev (1948) in the midbrain the following functions are represented, from the centre outwards ('pallium' or 'paleo-' refers to a phylogenetically old part of the brain):
in the endopallium: the physiologic regulation of water-retention and the concentrations of minerals, a very basic life-sustaining function
in the mesopallium (connected with the corpus striatum): instinctive behaviour to protect an individuals identity, including e.g. self-expressive movements,
in the ectopallium (well developed in mammals and primates): voluntary behaviour and practised skills, based on perception and cognition.
Referring to Altmann (1966) and MacLean (1975), Oliverio (1978) has proposed a transition from behavioural rigidity to plasticity in systems from the centre of the brain to the surface:
the spinomedullary area: innate reflexes that resist modification by learning
the paleocephalic region (mesencephalon, diencephalon and limbic system): recurring nourishing and servicing activities, behaviours of an appetitive or agonistic nature, and control of circadian energy-deploying processes. What has originally been an instinctive, inborn mode of execution can be modified by interaction with the environment
the neencephalic region: is the source of highly adaptive, variable behaviours, not directly programmed by inborn mechanisms but the result of individual development in a given environment.
It thus appears that a concentrically layered ground-plan of the human neural organisation is firmly established. With every layer that has been added during evolution the whole system was reassembled and brought up to date so as to secure the optimal exchange between the layers.