Understanding the Role of Sustained Attention and Effort in Arm Non-use in Stroke

Female physical therapist working with an older patient to build arm strength.

Jane suffered a stroke that impacts the sensation, strength, and dexterity of one of her arms.  She worked hard in inpatient neurorehabilitation, and assessments showed that her capacity to use the arm greatly improved.  When she returned home, however, her spouse noticed that she continues not to use the affected arm much in daily activities, preferring to rely on the other arm or to ask others for help. In fact, over time her use of the affected arm actually seemed to be decreasing.

One of the most challenging aspects of neurorehabilitation of stroke is that many individuals with adequate sensory-motor recovery and capacity to use their impaired arm do not actually do so.

Instead, there is a maladaptive pattern of over-use of the relatively intact arm, resulting in a vicious cycle in which the affected arm loses the gains that resulted from neurorehabilitation.  Can we identify the factors that make people likely to show this pattern of non-use?

One obvious factor might be the ability level of the affected arm:  people clearly favor their less-impaired arm if the impaired arm is particularly limited.  Working with a team from University of Southern California (USC), the MRRI Cognition and Action Lab headed by MRRI Associate Director Laurel Buxbaum, PsyD, performed a study showing that even when the severity of arm impairment is taken into account, a second factor—sustained attention – plays an important role in determining whether individuals are likely to use that arm. 

The researchers suggest that this pattern fits with the importance of sustained attention and ability to expend effort in a variety of cognitive and motor tasks, and with the idea that arm use occurs on the basis of an implicit cost-benefit analysis.  In individuals who have suffered a stroke, the reduced sensory-motor capacity of the impaired arm requires extra sustained attention and effort to overcome.  That is, movement comes at a greater “cost”. At the same time, however, the stroke diminishes the ability to deploy attention and effort. “To shift the cost-benefit relationship”, says Dr. Buxbaum, “we need to increase the degree to which use of the impaired arm is associated with reward”.

Neurorehabilitation programs can shift the cost-benefit relationship to favor arm use in a variety of ways.  Some direct ways including “gamifying” arm use via virtual reality and other motivating games, or allowing accumulation of points or rewards for arm use.  In addition, therapists can use goal-setting, peer support groups, family involvement with goals, and frequent check-ins to boost the reward associated with using the impaired limb.  In fact, therapies that have been associated with such benefits (sometimes termed “transfer packages”) have generally been more successful than those that do not.

Dr. Buxbaum and her colleagues from USC recently published a peer-reviewed study on the factors determining non-use in the journal Neurorehabilitation and Neural Repair.  Along with MRRI Institute Scientist Shailesh Kantak, PhD, the researchers are in the process of developing a funding proposal for follow-up research.

Research Spotlight: The Neuroplasticity and Motor Behavior Laboratory

Two researchers conducting motor behavior tests on a participant

After a stroke, about 80% of patients experience significant disability such as loss of function of one arm. This can lead to reduced quality of life and loss of independence. While rehabilitation research has begun to test novel strategies to improve arm function after stroke, the progress in neurorehabilitation is significantly limited by our understanding of how the nervous system participates in the control, coordination, and learning of arm movements after stroke. The goal of the Neuroplasticity and Motor Behavior Laboratory (NMBL) is to help improve the quality of life of stroke survivors by optimizing motor recovery through a better understanding of the mechanisms involved in motor control and learning. Currently, there are multiple exciting projects investigating different features of motor function in the arm after stroke.

From applying toothpaste on our toothbrush in the morning to pulling our blanket at night, we constantly engage both arms to accomplish tasks efficiently. Despite the ubiquitous nature of bimanual actions, current rehabilitation focuses on remediation of unilateral deficits of the weaker hand. It is thus not surprising that most unilateral therapy approaches improve unilateral performance, but they fall short of improving patient activity levels or participation in daily life. Our first project, funded by the NIH, identifies abnormalities in coordination between the two arms during different classes of bimanual actions in individuals with stroke. We acquire objective kinematic (movement) and kinetic (force) data from individuals with and without stroke as they interact with instrumented objects. In particular, we are interested in determining the extent to which unimanual impairments influence bimanual coordination deficits after stroke. Our preliminary analyses, published in the Archives of Physical Medicine and Rehabilitation, suggest task-dependent coordination deficits in bimanual coordination after stroke. Actions where two hands accomplish common goals (e.g., picking up a box with both hands) engage hands in a more coordinated fashion than those where each hand is accomplishing independent goals (e.g., each hand picking up a separate box). Currently, we are working on detailed analyses of movement and force data to test our hypotheses and report our findings.

While bimanual coordination deficits are evident in individuals with stroke, we are far from determining the best possible ways to remediate them. Sophisticated behaviors like bimanual coordination are complex, and they rely on interaction between motor, cognitive, and perceptual systems; thus, it is important to determine how motor and perceptual task demands influence learning of bimanual movements. Using an innovative bimanual reaching task in a virtual environment, we manipulate perceptual and motor demands to optimize training parameters of bimanual learning. Increasingly, we are also recognizing that responses to treatment in neurorehabilitation show significant inter-individual variability. To determine which patients benefit the most from bimanual learning, we use state-of-the-art neuroimaging and neurostimulation techniques to identify how an individual’s brain lesion and neural connectivity contribute to bimanual coordination and learning. This important project, funded by our NIH-NICHD R01 grant, aims to provide fundamental understanding of brain-behavior relationship for bimanual coordination and bimanual learning after stroke, and it set the stage for future investigations aimed at the development of intervention protocols to improve bimanual coordination for more complete functional arm recovery.

Some of the NMBL’s ongoing research is in collaboration with other scientists at MRRI, such as Laurel Buxbaum, PsyD. These projects investigate the effects of hemispheric specialization on goal-directed real world actions through systematic investigation of motor behavior as well as related cognitive and neuroimaging markers in stroke survivors with left and right hemisphere damage.

Stroke causes significant functional limitations that can lead to poor quality of life, and research conducted by the scientists and research assistants within NMBL and MRRI is providing important new knowledge to advance neurorehabilitation for people with stroke.