Patients who experience strokes or traumatic brain injury (TBI) need no longer accept that a resulting loss of limb functioning is gone forever. Instead they can tap an emerging therapy developed by Edward Taub, PhD, the recipient of this year's APA Distinguished Scientific Contribution Award. Taub described the behavioral and neuroscience underpinnings of the intervention, constraint-induced (CI) movement therapy, in his award address at APA's 2004 Annual Convention in Honolulu.
In several controlled empirical studies and replications, Taub and his colleagues at the University of Alabama at Birmingham have found that CI therapy helps patients regain a significant amount of their former mobility--well beyond what regular physical therapy usually delivers. To do that, CI therapy harnesses two neurobehavioral processes:
Intensive operant behavioral training, or "shaping." Clinicians train patients to use the impaired limb for daily tasks and to resist using the corresponding healthier one. Such training involves a clinician modeling daily-living tasks and reinforcing a patient's progressive improvement in performing them, step by step.
Massive brain neuronal reorganization. After injury, patients typically compensate by increased use of the healthier limb; consequently, the part of the brain responsible for moving the weaker arm shrinks. By forcing exercise on the weaker limb, CI therapy instead teaches the brain to rewire itself by assigning new neurons to moving that limb.
The technique adds to growing evidence of the brain's plasticity throughout the lifespan and dislodges a pre-1980s view that the brain is hardwired, said Taub.
"The belief was that the adult nervous system, when injured, could not repair or reorganize itself," said Taub. That view left millions of patients with chronic stroke with mostly untreated motor deficits, he said. "With new understanding and CI therapy," Taub continued, "there is now hope for this large population of patients with chronic stroke and TBI. There are several hundred thousand new cases of such patients each year in the U.S. alone."
Basic research origins
Taub's insights began in his basic research on monkeys with colleagues A.J. Berman, MD, and Harriet Knapp, PhD. In those studies, he surgically abolished all sensation from one forelimb by severing the sensory or dorsal roots of spinal nerves serving that limb. This led to loss of movement of that arm but spared use of the other arm--mimicking what often occurs in humans with stroke or other forms of brain injury. Next he restrained the monkeys' healthy forelimbs, compelling them to reuse the deafferented limbs, which they otherwise avoided doing.
Though supported by the National Institutes of Health, the research spurred, in the early 1980s, a People for the Ethical Treatment of Animals case against Taub alleging animal abuses. (Several animal rights activists, in fact, demonstrated during Taub's convention talk.)
APA played a significant role in Taub's legal defense, and he was eventually exonerated of all charges. After that, he published his results, including his finding that monkeys--through constraint of the healthy limb and training of the injured one--"learned" to use their deafferented limbs for everything from climbing and walking to picking up food.
He adapted the finding to humans, and CI therapy was born.
A modern technique
Of course, noted Taub, the transfer from monkeys to humans isn't exact. For example, in people, concentrated movement of the affected limb proves more helpful than restraint of the less affected one.
Accordingly, in Taub's ongoing research, CI therapy practitioners concentrate on patients' impaired arms--requiring patients to use them in repetitive tasks. Before training, CI therapists make "behavioral contracts" with patients and their caregivers, in which they promise to use the impaired limb exclusively for agreed-on activities, and keep a diary of the limb's progress during daily tasks.
Studies by Taub and his colleagues indicate that through CI therapy stroke patients can increase their spontaneous use of an injured limb by approximately 50 percent, while patients with stroke who undergo regular physical therapy show no such increase.
Researchers who have replicated these findings include several international teams, such as one led by German researcher Wolfgang H.R. Miltner, PhD, and co-authored by Taub. That study reached a similar result with 15 participants and was published in the American Heart Association journal Stroke (Vol. 30, No. 3) in 1999. Taub has also produced similar findings in a placebo-controlled experiment involving 40 patients and reported in 1999 in the Journal of Rehabilitation Research and Development (Vol. 36, No. 3). In all, claimed Taub, he has successfully treated more than 500 patients with chronic stroke and TBI.
Moreover, in neuroimaging and brain-mapping studies, he's found that brains of CI therapy patients look different from those of other stroke patients: A much larger region of the motor cortex on the injured side of the brain (and in about half the patients the motor cortex on the uninjured side of the brain) activates when they use their injured limbs.
"This shows that not only does the CNS [central nervous system] produce behavior, but behavior can have an equally profound reciprocal effect on the CNS--in this case a therapy-induced increase in motor ability," said Taub, noting that other preliminary research he's conducting suggests CI therapy can also help rehabilitate young children with cerebral palsy and patients with a number of other CNS disorders.
Further information and research citations are available on Taub's Web site at www.psy.uab.edu/taub.htm.
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