New model of how brain functions are organized may revolutionize stroke rehab

by Seth Palmer
Overlap images showing locations of lesions between groups with right and left hemisphere damage (color scale of magenta to red shows increasing overlap). Lesions are confined to either left or right hemisphere. Credit: Sainburg Lab

(Medical Xpress)—A new model of brain lateralization for movement could dramatically improve the future of rehabilitation for stroke patients, according to Penn State researcher Robert Sainburg, who proposed and confirmed the model through novel virtual reality and brain lesion experiments.

Since the 1860s, neuroscientists have known that the is organized into two hemispheres, each of which is responsible for different functions. Known as neural lateralization, this functional division has significant implications for the control of movement and is familiar in the phenomenon of .

Understanding the connections between neural lateralization and is crucial to many applications, including the rehabilitation of . While most people intuitively understand handedness, the neural foundations underlying motor have until recently remained elusive, according to Sainburg, professor of and neurology and participant in the neuroscience and physiology graduate programs at the University's Huck Institutes of the Life Sciences.

Research by Sainburg and his colleagues in the Center for Motor Control and published in the journal Brain has revealed a of motor lateralization that accounts for the neural foundations of handedness. The discovery could fundamentally change the way is designed.

"Each of the brain is specialized for different aspects of motor control, and thus each arm is 'dominant' for different features of movement," said Sainburg. "The dominant arm is used for applying specific force sequences—such as when slicing a loaf of bread with a knife—and the other arm is used for impeding forces to maintain stable posture, such as holding the loaf of bread. Together these specialized control mechanisms are seamlessly integrated into every day activities.

"Our research has shown that this integration breaks down in neural disorders such as stroke, which produces different motor deficits depending on whether the right or left hemisphere has been damaged," Sainburg continued. "Traditionally, physical rehabilitation professionals have used the same protocols to practice movements of the paretic arm, regardless of the hemisphere that has been damaged. Our research shows that each arm should be treated for different control deficits, and it also indicates that therapists should directly retrain patients in how to use the two arms together in order to recover function."

In preparing to test their model, Sainburg and his team selected study participants from the New Mexico Veterans Administration Hospital and Penn State Milton S. Hershey Medical Center based on specific criteria in order to accurately distinguish the motor control mechanisms specific to each brain hemisphere. Participants were then asked to perform a series of tasks on a virtual reality interface, programmed and designed by Sainburg, which allowed the researchers to record detailed 3D position and motion data. The data for all the participants' hand trajectories and final positions were then aggregated to compare the effects of left versus right hemisphere damage on different aspects of control.

"Our results indicated that while both groups of patients showed similar clinical impairment in the contralesional arm, this was produced by different motor control deficits," Sainburg said. "Right hemisphere damaged patients were able to make straight movements that were directed toward the targets, but were unable to stabilize their arms in the targets at the end of motion. In contrast, left hemisphere damaged patients were unable to make straight and efficient movements, but had no difficulty stabilizing their arms at the end of motion. These results confirmed that each hemisphere contributes unique control to its contralesional arm, verifying why our arms seem different when we use them for the same tasks."

Results mirror those of Sainburg's prior studies of motor deficits in unilateral stroke patients, focused on the ipsilesional arm, which formed the basis for his model of lateralization.

"Because both arms in stroke patients show motor deficits that are specific to the hemisphere that was damaged, we have concluded that the left arm is not simply controlled with the right hemisphere and vice versa," Sainburg said. "This is a revolutionarily new perspective on sensorimotor control: each hemisphere contributes different to the coordination of both arms, regardless of which arm is considered dominant."

Sainburg and his colleagues are currently designing follow-up studies that will aid the development of new rehabilitation protocols addressing the specific motor deficits associated with each hemisphere.

Related Stories

Muscle 'synergies' may be key to stroke treatment

Oct 20, 2009

Researchers at MIT and San Camillo Hospital in Venice, Italy, have shown that motor impairments in stroke patients can be understood as impairments in specific combinations of muscle activity, known as synergies.

Rehab robots lend stroke patients a hand

Aug 11, 2011

Robot-assisted therapy has measurable benefits for patients with a weaker arm following a stroke. This is according to new research featured in the journal Clinical Rehabilitation, published by SAGE, which is the first to use ...

Improving post-stroke rehabilitation with neurotransmitter

Mar 11, 2011

In many patients, fine motor skills remain impaired after a stroke. A recent study has shown that the neurotransmitter noradrenaline may be able to reduce such deficits. This finding could result in the development ...

Study finds emotion reversed in left-handers' brains

May 02, 2012

The way we use our hands may determine how emotions are organized in our brains, according to a recent study published in PLoS ONE by psychologists Geoffrey Brookshire and Daniel Casasanto of The New School for Social Resear ...

Recommended for you

Link seen between seizures and migraines in the brain

6 hours ago

Seizures and migraines have always been considered separate physiological events in the brain, but now a team of engineers and neuroscientists looking at the brain from a physics viewpoint discovered a link ...

Neuroscience: Why scratching makes you itch more

12 hours ago

Turns out your mom was right: Scratching an itch only makes it worse. New research from scientists at Washington University School of Medicine in St. Louis indicates that scratching causes the brain to release ...

User comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.