Redundancy of the motor control system is an important feature that gives the central control structures options for solving everyday motor problems. The choice of particular control patterns is based on priorities (coordinative rules) that are presently unknown. Motor patterns observed in unimpaired young adults reflect these priorities. We hypothesize that under certain atypical conditions, which may include disorders in perception of the environment and in decision making, structural or biochemical changes within the central nervous system (CNS), and/or structural changes of the effectors, the central nervous system may reconsider its priorities. A new set of priorities will reflect the current state of the system and may lead to different patterns of voluntary movement. Under such conditions, changed motor patterns should be considered not pathological but rather adaptive to a primary disorder and may even be viewed as optimal for a given state of the system of movement production. Therapeutic approaches should not be directed toward restoring the motor patterns to as close to “normal” as possible but rather toward resolving the original underlying problem. We illustrate this approach using, as examples, movements in amputees, in patients with Parkinson's disease, in patients with dystonia, and in persons with Down syndrome.

This article describes a series of experiments directed toward the following questions: (1) Do signals from musculotendinous receptors reach consciousness? (2) Does feed-forward information of muscular force and expected extent of voluntary movement exist? To answer these questions data from voluntary compression of springs and strain-gauge have been analysed in healthy young subjects and in patients with unilateral focal lesions of the cerebral hemispheres.

By successive elimination of information from other sources it was possible to verify that receptors in muscles and tendons do signal movement magnitude and muscular tension to the cerebral cortex, and that this information does indeed reach consciousness. There also exists a feed-forward mechanism signalling parameters of voluntary contraction. However, it is unclear whether peripheral, subcortical, or intracortical loops are directly involved. Perception of signals of muscular tension is abolished by lesions of the contralateral cortex near the central sulcus. It is possible that there exist separate cortical projection areas for kinaesthetic signals from muscles and from joints.