Post-lesion functional restoration of hand dexterity and the principle of motor equivalence

The paper addresses the issue of functional recovery and particularly on adaptive changes that can occur shortly after brain lesions, i.e. before any structural changes may occur. In goal-oriented tasks, the organism adapts to new constraints by changing strategies and/or by selecting other effectors to reach the goal. Goal achievement with variable movement configurations is a typical feature of purposeful motor actions in healthy subjects as well as in patients following brain lesions. Lashley (1933) was first to describe this under the term of Motor Equivalence. Own lesion studies in subhuman primates underscore the important adaptive properties of the brain as evidenced by measures of task performance before and after cortical lesion. Another aspect is the variable and strongly use-dependent size of a given cortical map. Rapidly occurring post-lesion reorganizations in brain representations may contribute to functional restoration, especially if combined with extensive training. Functional imaging has shown that secondary motor areas are often implicated at an early stage in the process of functional recuperation. Finally, an example of abnormal structural organization of the motor cortex is illustrated in a patient who had acquired a large lesion in one hemisphere during early development. Brain imaging and transcranial magnetic stimulation revealed that the intact hemisphere had taken over control of both arms and hands.