New approaches to stroke rehabilitation

Complementary hemispheric dominance theory is basis for new physical therapies.

Past newsletters summarized ways to recover from brain injuries. These include:

Real advances in Rehab Medicine. This Memorial Day, let's bring the vets some good healing

Music is Magic. Potent medicine for both body and mind.

Protection and regrowth of neurons. Hypoxic brain injury, peripheral denervation, myelin loss - here are ways to recover?

Now we report progress in therapies targeted for stroke recovery. It is challenging the longstanding dogma that motor control is strictly lateralized to each brain hemisphere.

Summary of the complementary dominance hypothesis of motor lateralization and its application in remediating functional motor deficits of the ipsilesional arm in stroke survivors. The complementary dominance model of motor lateralization highlights distinct yet complementary functional contributions of each hemisphere to movement control (top panel). The dominant (left) hemisphere specializes in optimal control of limb dynamics and is therefore advantaged for well-established behavioural patterns under predictable circumstances. The non-dominant (right) hemisphere specializes in impedance control, which regulates steady-state limb position and responses to unexpected stimuli in the environment. Unilateral stroke results in hemisphere-specific motor deficits in both the contralesional and ipsilesional arms that are functionally limiting and consistent with the complementary dominance hypothesis. Left hemisphere stroke leads to deficits in initial direction accuracy, resulting in curved hand trajectories (middle panel, right). By contrast, right hemisphere stroke impairs final position accuracy, as demonstrated by larger deviations from the target location (middle panel, left). Based on these observations, we are now testing a novel training intervention to remediate functional motor deficits of the ipsilesional arm for chronic, severely impaired stroke survivors. The intervention includes hemisphere-specific virtual-reality training (bottom panel, top ro -w) and real-world dexterity training (bottom panel, lower row), which we expect to translate to improved functional independence. —NM Kitchen, et al.

The complementary dominance hypothesis is a novel model of motor lateralization substantiated by decades of research examining interlimb differences in the control of upper extremity movements in neurotypical adults and hemisphere-specific motor deficits in stroke survivors. In contrast to earlier ideas that attribute handedness to the specialization of one hemisphere, our model proposes complementary motor control specializations in each hemisphere. The dominant hemisphere mediates optimal control of limb dynamics as required for smooth and efficient movements, whereas the non-dominant hemisphere mediates impedance control, important for countering unexpected mechanical conditions and achieving steady-state limb positions. Importantly, this model proposes that each hemisphere contributes its specialization to both arms (though with greater influence from either arm's contralateral hemisphere) and thus predicts that lesions to one hemisphere should produce hemisphere-specific motor deficits in not only the contralesional arm, but also the ipsilesional arm of stroke survivors – a powerful prediction now supported by a growing body of evidence. Such ipsilesional arm motor deficits vary with contralesional arm impairment, and thus individuals with little to no functional use of the contralesional arm experience both the greatest impairments in the ipsilesional arm, as well as the greatest reliance on it to serve as the main or sole manipulator for activities of daily living. Accordingly, we have proposed and tested a novel intervention that reduces hemisphere-specific ipsilesional arm deficits and thereby improves functional independence in stroke survivors with severe contralesional impairment.

Remediating the ‘good hand’

Two hypotheses of motor lateralization A, the global dominance hypotheses posit that the dominant right arm should exhibit superior performance on all aspects of motor function (thick red arrow) compared to the non-dominant left arm (thin blue arrow), with influence of the ipsilateral cortices commonly overlooked. B, the complementary dominance hypothesis posits that each hemisphere has different, but complementary, specialized functional contributions to movement control. Under this hypothesis, both hemispheres contribute to control of unilateral arm movements, though with a greater influence of the specialized function of the contralateral hemisphere.

The complementary dominance hypothesis proposes different specialized, yet complementary, roles of the left and right hemispheres for motor control. Both brain hemispheres contribute to aspects of movement bilaterally - both sides of the body access both sides of the brain. Both sides use the same control systems, but each side relies more on the specialization of the opposite side brain hemisphere—the one more closely connected to control of that side. Specific tasks show better performance by the non-dominant arm. Thus, hemisphere-specific components of movement are selectively impaired in both arms as a result of left or right hemisphere damage following a stroke.

For right-handers, the dominant left hemisphere is specialized for optimal control of limb dynamics, resulting in smooth and mechanically efficient movement trajectories for the dominant arm. Conversely, the non-dominant, right hemisphere behaves as if an impedance controller, resulting in better stabilization of the left arm under unpredictable conditions, and with more stable achievement of steady-state final positions during reaching movements. For left-handers, the same specializations should occur, but in the opposite hemisphere and arms.

The research team analyzed the data from a large-scale clinical trial that tested the effectiveness of therapies informed by the complementary dominance hypothesis. They examined whether a person's non-dominant arm and hand are better at some tasks or elements of tasks than the dominant arm.

Results showed that the dominant hemisphere of the brain—the left hemisphere in right-handed people—was better at smooth, accurate and efficient limb movements. Research also demonstrated that the non-dominant, right hemisphere of the brain was better at stabilizing the left arm in unpredictable situations.

Using these insights, researchers developed potential rehabilitation protocols for the less-impaired arm of stroke victims. In a pilot proof of concept study, clinicians asked people who had a stroke in the left hemisphere of their brain to play a virtual air hockey game with their left hand in order to rehabilitate the accuracy of their directional movement. Patients who suffered a stroke in the right hemisphere of their brain were given a maze-tracing game for their right hand in order to rehabilitate the accuracy of the destination of their hand. After three weeks of training, people were 19% faster at completing a test to measure the dexterity of stroke survivors' hands [the Jebsen–Taylor Hand Function Test] - results which were durable, lasting at least six weeks.

Currently ongoing, is a large-scale clinical trial involving severely paretic stroke survivors, which compares remediation targeting only the contra- lesional arm to that of targeting only the ipsilesional arm. Expected is a greater carry over to functional independence for the group with the ipsilesional arm intervention.

For stroke rehab… let the games begin!

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REFERENCES

NM Kitchen, et al. The complementary dominance hypothesis: a model for remediating the 'good' hand in stroke survivors. The Journal of Physiology (2024). DOI: 10.1113/JP285561

Alternative understanding of brain leads to new treatments for stroke patients (2024, July 12) https://medicalxpress.com/news/2024-07-alternative-brain-treatments-patients.html