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COPYRIGHT 2007 American Physical Therapy Association, Inc.
In the past decade, several critical reviews of poststroke rehabilitation (1-4) have indicated that task-oriented interventions can induce more substantial functional improvements than neuromuscular reeducation approaches for which weighting of supportive evidence is sparse. One such approach is called "constraint-induced movement therapy" (CIMT), also called "CI therapy."
A Brief Historical Primer
Constraint-induced movement therapy originates from seminal studies by Taub (5) of monkeys that had undergone deafferentation. Taub demonstrated that animals forced to use the insensate upper extremity through immobilization of the intact limb for short periods could soon learn to use the insensate limb even when the use of both limbs was possible. Training of the monkeys that had undergone deafferentation during the forced-use period was achieved through successive approximations as the basis for shaping intended movement. The animals would be rewarded as they progressively reached toward and subsequently grasped objects. Taub proposed that the animals had undergone "learned nonuse" of the affected limb and, given the appropriate behavioral training, could relearn to use it indefinitely. Although the duration of the effect of deafferentation was never assessed, Taub proposed that this approach be used for patients with hemiparesis and presumed that the diaschisis after stroke led to a learned suppression of movement comparable to the suppression of the spontaneous limb use in monkeys that had undergone cervical deafferentation.
At about the same time at which Taub was undertaking a series of elegant subhuman primate studies (6-8) from which the learned nonuse theory was formulated, Basmajian was initiating studies on electromyographic biofeedback applications to patients with stroke. (9-11) This approach consisted of monitoring individual limb muscles, usually with surface electrodes, and providing patients with visual and auditory cues about muscle activity. Electromyographic responses could be conditioned through the use of threshold detectors, and signal amplification settings could be controlled by clinicians to modify the presentation of auditory or visual cues to patients on the basis of whether responses were being "down-trained" (as in the case of hyperactive muscles) or "up-trained" (weakened antagonists).
These studies led to a series of subsequent investigations (12,13) that indicated that the primary predictor of the independent use of the hemiparetic upper extremity in patients with chronic stroke was the ability to initiate elbow, wrist, and finger extension. (14,15) This capability became the primary inclusion criterion for what was initially described as "forced use." (16,17) Forced use is defined as the process through which a patient is made to use the hemiparetic upper extremity through immobilization of the better limb in a sling or while wearing a mitt during most waking hours. During such time, the patient undertakes activities determined collaboratively with the clinician but performed in the home environment. Over a 2-week time interval, the patient is free to contact the therapist for alterations in tasks or questions regarding compliance. Many studies (18-21) continue to use this forced-use approach for patients after stroke.
Constraint-induced movement therapy includes forced use but also includes one-on-one training for as much as 6 hours per day over several weeks as well as repetitive task practice and adaptive task practice (also called "shaping"). Repetitive task practice refers to continuous efforts to execute movements that usually are repeated, for example, eating, grooming, or brushing teeth. During such efforts, the kinematics of the movements can be varied (made more challenging) on the basis of considerations of a patient's reacquisition of movement control. Therefore, the only interruptions that occur are those used to make the execution of the tasks easier or more difficult.
Adaptive task practice is a form of operant or instrumental conditioning (associating a reward with a correct response as a basis for reinforcing the correct response) characterized by repetitions of a defined movement, such as picking up blocks and moving them toward a pall, in a series of trials. Each trial has a defined duration, and often a participant is asked either to increase the successful numbers of repetitions or to reduce the time to complete the task demands successfully with one effort. During these efforts, the patient is coached or encouraged by the therapist. The patient then is shown a performance record over a number of trials and should be motivated to perform even more optimally on the basis of progressive improvement over trials. With respect to CIMT, this training procedure was developed by Taub and his group at the University of Alabama at Birmingham and contains the intense treatment approach and additional home work assigned along with a mutually agreed-on behavior contract as its signature piece (see Taub and Uswatte (22) for a comprehensive review of the basis for CIMT).
Modified CIMT, as developed by Page and colleagues, (23-25) represents a distributed practice pattern in which the mitt is worn for several hours each day over a 10-week period and this home-based practice is supplemented with outpatient therapy several times each week. It is interesting that 27 years after the original formulation of CIMT, the ability of a patient to initiate finger extension has been validated as a primary predictor of the successful application of CIMT. (26)
Exploring a Model for Studying CIMT
An important consideration for CIMT is the belief that the intervention is behavioral in nature and, in fact, a case has been made that the signature piece of CIMT can be defined by the predominant, if not exclusive, use of adaptive task practice, also called shaping. (27) This statement would imply that other factors, such as the use of principles governing motor learning (or relearning) or motor control, are not essential considerations in the formulation and execution of CIMT. Several superb perspectives (28-31) can easily be interpreted as challenging this implication.
Although the facts that CIMT has been shown to modify brain activity, especially in the affected motor and premotor cortexes, and that interconnections from undamaged hemispheric structures can be engaged, (32) there is a need to explore mechanisms through which CIMT can induce neuroplasticity. Further questions involve the possible presence of neural substrates that impede movement initiation and whether these substrates might be susceptible to modification with CIMT.
The flow diagram depicted in Figure 1 superimposes on the fundamental model of learned nonuse developed by Taub and coworkers (27) (bold type) additional components supplied by Sunderland and Tuke (30) (italic type). These components can influence the reacquisition of limb use through compensatory learning. The perspective of Taub and coworkers is that specific behavioral retraining will reduce basic impairments as more normal function is restored. Under the learned nonuse paradigm (Fig. 1), cortical or subcortical pathology affecting motor output (as well as reduced limb cortical representation; see below) would result in poor function, even if the potential for use existed. Frustration, fatigue, and teaching of compensatory strategies (defined as learning to use the better upper extremity in the interest of time, convenience, and demonstration of ability) inevitably would produce learned nonuse behavior and, consequently, little initiative to use the impaired hand. The additional factors supplied by Sunderland and Tuke are referred to as "compensatory learning." This form of compensation is different from the compensatory use of the better limb. Specifically, compensatory learning includes behavioral factors, such as attention, motivation, and perceived sense of effort, (33) that contribute to a patient's reacquisition of unique motor skills through attention, motivation, effort, and control over motor outflow from preserved or accessible pathways. This new skill capability thus may facilitate restoration of the cortical representation of movement through task practice.
[FIGURE 1 OMITTED]
Therefore, this model would suggest that overcoming learned nonuse (Fig. 1, bold type) and improved compensatory learning (Fig. 1, italic type) both contribute to limb use after CIMT. One could deduce that factors such as attention and sense of effort are emergent behaviors that are manifested during CIMT training.
Although this behavioral linking of concepts is indeed intriguing, the model does call...
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