Adaptations occurring in the central nervous system (CNS) in the presence of pathology are not uniformly “good” for the organism when viewed in a functional context. A functional reordering of CNS priorities can be produced by allowing restructuring of the external context or through modification of neuromuscular physiology or anatomy designed to reduce the inherent restriction of functional movement in upper motor neuron syndrome. In fact, volitional control can often be “unmasked” through such interventions. Therapeutic interventions should not be directed toward “normalization” of motor patterns but should permit a functional reordering of CNS priorities that would otherwise not be possible.

It is difficult to chart “normal movements” in atypical populations, such as those with Parkinson's disease, because there is great variability in the pattern of motor changes, both within and between patients. However, the potential clinical implications of Latash & Anson's theme are positive and powerful.

Movement patterns in impaired gait are not selected by a smart central nervous system (CNS), but arise by virtue of mutual constraints of task, limitations in personal dynamics available for the task, and optimality criteria. An oscillatory model of gait cycle is presented that exemplifies this control and coordination scheme. Preferred gait patterns may be based on physical principles rather than CNS “coordinative rules.”

To understand the basic priorities of the central nervous system in human motor control, neurophysiological parameters are important. Certain H-reflex methods related to anticipatory postural control are particularly useful and may have therapeutic implications.

Priorities for movement reflect constraints deriving from the motor system, task goals, and physical environment. Atypical and typical populations alike set and reset priorities in response to constraints, and they do so at many processing loci and time scales. Efforts to understand what is atypical about a population should focus first on the constraints it encounters.

The guideline for therapy should be the improvement of the individual's functionality, not the acquisition of the ill-defined “goldstandard” of normal movement. However, Latash & Anson's suggestion that only primary causes of dysfunction should be treated is problematic for two reasons: First, the distinction between genuine and adaptive changes in motor performance is not always possible, and second, adaptive changes do not necessarily improve motor function, but may actually be detrimental to the system's performance.

The motor deficits observed in patients following some lesions of the central nervous system may be viewed as falling at one extreme of the continuum of possible motor behaviours. They are usually associated with an impaired ability to select and control specific movements from the available repertoire. Such movements may not be viewed as abnormal. However, it is unlikely that the primary motor deficits can all be considered adaptive.

It is the contention of Latash & Anson (L&A) that in atypical populations, such as those with cognitive, central neurological, or peripheral disorders, the central nervous system (CNS) is capable of producing more effective, though often less “normal,” movement patterns ifleft to its own devices. It is the aim of this commentary to extend their argument to other populations by pointing out the many parallels with development of movement patterns in sport.

The suggestion that movement disorders exhibited by people with central nervous system (CNS) dysfunction should be considered normal and therefore not rehabilitated is rejected from three standpoints: (1) the CNS does not always select the best movement patterns for optimal long term outcome, (2) there is literature demonstrating that rehabilitation enhances motor function and independence, and (3) there exists a capacity for motor recovery and motor skill learning following brain damage.

Latash & Anson propose that so-called abnormal movements may be stable and adaptive coordination and control solutions to task goals in action. Their interpretation of this established viewpoint is confused throughout in the persistent crossing of frames of reference, both in the description of movement and action and the proposed theory for motor control.

Latash & Anson's discussion of movements of “atypical” populations is potentially topical but unhelpful. Abnormal movements can be distinguished from any compensatory adjustments in Parkinson's, Huntington's, and Alzheimer's diseases and schizophrenia. To suggest otherwise may do “atypical” populations and their caregivers a disservice. It would be more meaningful to discuss the relative modularity and separability of cognitive and motor processes.

Latash & Anson are commended for pointing out that investigators of atypical motor performance have too often failed to recognize the adaptive nature of many atypical movement characteristics. However, the authors' assumption that atypical motor patterns can be considered “normal” and, by implication, that it is futile to attempt to teach different patterns to patients that may be more functional, is criticized.

Observations are made on Latash & Anson's theme that changed motor patterns should not be viewed as pathological. Normality in motor control might be characterised in terms of qualitative differences in control mechanisms rather than differences in movement patterns. Understanding of the concepts implicit in instructions to subjects should be confirmed. Principles of energy expenditure in atypical movements are outlined. If restoration of normality is not adopted as a criterion for therapeutic intervention, what might be proposed as an alternative?

The assumption that adaptive changes in motor patterns are optimal is questioned. Instances are cited where alteration of the adaptive motor patterns may be warranted. Other issues discussed are: (1) the relationship between central nervous system (CNS) priorities and the individual's priorities, (2) the use of cognitive bypass strategies by impaired individuals, and (3) conceiving CNS priorities as coordinative rules.

Whereas Latash & Anson (L&A) have underscored the rearrangement or setting of new priorities, our primary focus is on preexisting central nervous system (CNS) priorities that become even more prevalent and intrusive under pathological conditions. The adaptations observed in the disordered motor system can often be understood against the backdrop of these primary CNS constraints. Even though this perspective has not been specifically addressed in the target article, we consider it complementary and not necessarily in opposition to L&A's primary thesis.

Normal infants show a wide range of “atypical” movements. These, like the movements of atypical and normal adults, are best characterized as solutions to motor problems. Motor patterns alone may not be precise indicators of neurological status.

We show that left-handers can be considered as a “special” population. We indicate that the asymmetries in performance exhibited by left-handers are due to a basic asymmetry in the underlying coordination dynamics that constrains bimanual coordination. In contrast to the claims of Latash & Anson, we argue that considerable knowledge has been gained regarding the essential equations of motion that govern biological coordination.

The argument that disordered or changed motor patterns can be adaptive or optimal given the constraints imposed is supported. Two major points of criticism are made, concerning the perceived superstates of the primary disorder and the absence of a systematic approach to identifying this adaptivity and optimality. We have tried to give the general outlines of such an approach to disordered movements from a dynamic systems perspective.

The target article pays insufficient attention to (1) the difficulties that arise when the term “normal” is used to describe motor skill behavior, and (2) the need to resist ascribing motor control to an intelligent central nervous system. A complex systems perspective is proposed with attractor states and periodicity identified as markers of atypical coordination and control.