ABSTRACT
Anyone familiar with the site plan for a large complex organisation will know that departments that need to work closely together are more effective if they are physically located in close proximity or at least very well connected. Departments are often grouped together according to functional relationships and may even have offices together in a single building or the floor of a building. This principle is followed in the brain too whose site plan has evolved over thousands of years with ineffective layouts going out of business. The result of this selection process is a personally customised yet anatomically similar structuring of our cerebrum, the most evolved part of our brain, into separate lobes in the cerebral cortex (see Figure 1.1), our limbic system (see Figure 9.1), and our basal ganglia (see Figure 10.1). Each of these major structures contains clusters of functions that interact to form meta-functions, analogous to a division within an organisation. Anyone familiar with a large business knows that this arrangement into functionally specialised zones carries the danger of a silo mentality developing so that inter-departmental and inter-functional communication mechanisms are needed if the organisation is to pull in the same direction towards shared goals. In the brain such cross-functional communication is the role of white matter organised as association tracts within a hemisphere, commissures between hemispheres and projection tracts between the different levels. A matrix concept is a useful metaphor for the functioning of the brain. The more our brains evolved the more of a matrix structure has developed, moving beyond the inflexible limitations of a top-down hierarchical functional silo approach. There is also evidence for role flexibility so that variations in the functional layout may be anticipated from individual to individual and over time.
