Closely related to the theory of reorganization of the brain following injury is the concept of 'redundancy'. This refers to the way that the brain seems to have a system of duplicated pathways for controlling the same function. This means that if one pathway is damaged or destroyed, the possibility exists that one of the duplicated pathways may take over.
According to Granit: 'Everywhere one finds important functions secured by a redundancy of pathways, and also by a multiplicity of mechanisms capable of producing the same end effect.' In looking at why redundancy occurs, Granit states: 'The brain has to cope with both basic predictability and Nature's capriciousness. This is done by having strictly designed pathways on one hand, and an immense multiplication of possibilities on the other. This immense multiplication is reminiscent of the apparent wastefulness of plants and animals in producing seeds, sperm and eggs, but is necessary to ensure the continued adaptation of the species'.
In humans, the normal development of the brain seems to result in a certain degree of redundancy. Granit feels that as the brain matures, some circuits become dominant while others appear to be relegated to a recessive role. Either that or they are overridden and in turn controlled in part by newer pathways. Ayers refers to the control exerted by the higher parts of the brain as being additional, but not substitute, control. She says: 'As the nervous system evolved to meet the expanding needs of existence, the newer structures tended to duplicate older structures and functions, and improve on them rather than to devise different functions. Nature, like some people, hesitates to throw anything away; instead, it will modify the function of the older structure. Thus the same kinds of functions are repeated at several levels of the brain. The higher levels, as they developed, also remained dependent upon the lower structures.'
Moore explains what happens to the lower brain levels as the higher parts take over: 'As higher level functions develop, the older pathways that once performed a patterned response are no longer vital for carrying out a particular activity pattern. This is not to say that these older routes die out or fade away. They remain, and function in the normal individual in maintaining the overall integrity of the nervous system. However, they function in a minor way in comparison to the newer pathways.'
According to Moore, these redundant levels may be utilized following an injury that destroys parts of the higher centres: 'When higher functions are lost or damaged due to brain injury, the older, once-utilized, recessive or alternate routes remain. If these can be tapped or strengthened - by using them in the same way, or in a manner similar to the way they were originally used - then these older pathways may constitute viable "alternate potentials" through which functional alternatives may be gained.