Motor Deficits in the Ipsilesional Arm of Severely Paretic Stroke Survivors Correlate With Functional Independence in Left, but Not Right Hemisphere Damage

Handy divisions: Hand-specific specialization of prehensile control in bimanual tasks

When hammering a nail, why do right-handers wield the hammer in the right hand? The complementary dominance theory suggests a somewhat surprising answer. The two hands are specialized for different types of tasks: the dominant for manipulating objects, and the non-dominant for stabilizing objects. Right-handers wield the moving object with their right hand to leverage the skills of both hands. Functional specialization in hand use is often illustrated using examples of object manipulation. However, the complementary dominance theory is supported by wrist kinematics rather than object manipulation data. Therefore, our goal was to determine whether this theory extends to object manipulation. We hypothesized that hand-specific differences will be evident in the kinematics of hand-held objects and in the control of grip forces in right-handed individuals. Right-handed participants held two instrumented objects that were coupled by a spring. They moved one object while stabilizing the other object in various bimanual tasks. They performed motions of varying difficulty by tracking predictable or unpredictable targets. The two hands switched roles (stabilization vs movement) in various experimental blocks. The changing spring length perturbed both objects. We quantified the movement performance by measuring the objects' positions, and grip force control by measuring grip-load coupling in the moving hand and mean grip force in the stabilizing hand. The right hand produced more accurate object movement, along with stronger grip-load coupling, indicating superior predictive control of the right hand. In contrast, the left hand stabilized the object better and exerted a higher grip force, indicating superior impedance control of the left hand. Task difficulty had a weak effect on grip-load coupling during object movement and no effect on mean grip force during object stabilization. These behavioral results demonstrate that complementary dominance extends to object manipulation, though the weak effect of task difficulty on grip characteristics warrants further investigation. Neurophysiological investigations can now examine the hemisphere-specific neural mechanisms underlying these behavioral differences.

Direction-dependent differences in the quality and quantity of horizontal reaching in people after stroke

Arm reaching is often impaired in individuals with stroke. Nonetheless, how aiming directions influence reaching performance and how such differences change with motor recovery over time remain unclear. Here, we elucidated kinematic parameters of reaching toward various directions in people with poststroke hemiparesis in the subacute phase. A total of 13 and 15 participants with mild and moderate-to-severe hemiparesis, respectively, performed horizontal reaching in eight directions with their more-affected and less-affected sides using an exoskeleton robotic device at the time of admission to and discharge from the rehabilitation ward of the hospital. The movement time, path length, and number of velocity peaks were computed for the mild group (participants able to reach toward all eight directions). In addition, the total amount of displacement (i.e., movement quantity) toward two simplified directions (mediolateral or anteroposterior) was evaluated for the moderate-to-severe group (participants who showed difficulty in completing the reaching task). Motor recovery was evaluated using the Fugl-Meyer assessment. The mild group showed worse values of movement parameters during reaching in the anteroposterior direction, irrespective of the side of the arm or motor recovery achieved. The moderate-to-severe group exhibited less movement toward the anteroposterior direction than toward the mediolateral direction at admission; however, this direction-dependent bias in movement quantity decreased, with the movement expanding toward the anteroposterior direction with motor recovery at discharge. These results suggest that direction-dependent differences in the quality and quantity of reaching performance exist in people after stroke, regardless of the presence or severity of hemiparesis. This highlights the need to consider the task work area when designing rehabilitative training.NEW & NOTEWORTHY Arm reaching, a fundamental function required for the upper extremities, is often impaired after stroke due to muscle weakness and abnormal synergies. Nonetheless, how aiming directions influence performance remains unclear. Here, we report that direction-dependent differences in the quality and quantity of reaching performance exist, surprisingly regardless of the presence or severity of hemiparesis. This result highlights the need to consider the task work area when designing rehabilitative training.

Correlation between Selective Motor Control of the Lower Extremities and Balance in Spastic Hemiplegic Cerebral Palsy: a randomized controlled trial

BACKGROUND

Children with cerebral palsy (CP) have motor deficits caused by spasticity, weakness, contractures, diminished selective motor control (SMC), and poor balance. The purpose of the current study was to evaluate the influence of mirror feedback on lower extremity selective motor control and balance in children with hemiplegic cerebral palsy. Understanding the relationship between SMC and balance will help children with hemiplegic CP receive more appropriate therapies.

METHODS

Forty-seven children of both sexes diagnosed with hemiplegic CP participated in the study. Group1 (Gr1 - control group) received conventional physical therapy training while group 2 (Gr2 - intervention group) received conventional physical therapy training in addition to bilateral lower extremity mirror therapy (MT). The primary outcome measure used was Selective Control Assessment of Lower Extremity scale (SCALE), while the secondary outcome measure was the Pediatric Balance Scale (PBS).

RESULTS

There were significant differences in Selective Control Assessment of Lower Extremity Scale (SCALE) and Pediatric Balance Scale (PBS) between both groups in favor of Gr2. After treatment, both groups improved significantly, yet Gr2 outperformed Gr1 by a large margin.

CONCLUSION

Mirror therapy may be a useful addition to home-based motor interventions for children with hemiplegic CP due to its relative simplicity, low cost, and high patient adherence. Additionally, it may help children improve their selective motor skills and balance.

TRIAL REGISTRATION

Current Controlled Trials using African Clinical Trials Registry website with ID number PACTR202105604636415 retrospectively registered on 21/01/202.

Object-centered sensorimotor bias of torque control in the chronic stage following stroke

When lifting objects whose center of mass (CoM) are not centered below the handle one must compensate for arising external torques already at lift-off to avoid object tilt. Previous studies showed that finger force scaling during object lifting may be impaired at both hands following stroke. However, torque control in object manipulation has not yet been studied in patients with stroke. In this pilot study, thirteen patients with chronic stage left hemispheric stroke (SL), nine patients with right hemispheric stroke (SR) and hand-matched controls had to grasp and lift an object with the fingertips of their ipsilesional hand at a handle while preventing object tilt. Object CoM and therewith the external torque was varied by either relocating a covert weight or the handle. The compensatory torque at lift-off (Tcom) is the sum of the torque resulting from (1) grip force being produced at different vertical finger positions (∆CoP × GF) and (2) different vertical load forces on both sides of the handle (∆Fy × w/2). When having to rely on sensorimotor memories, ∆CoP × GF was elevated when the object CoM was on the ipsilesional-, but decreased when CoM was on the contralesional side in SL, whereas ∆Fy × w/2 was biased in the opposite direction, resulting in normal Tcom. SR patients applied a smaller ∆CoP × GF when the CoM was on the contralesional side. Torques were not altered when geometric cues were available. Our findings provide evidence for an object-centered spatial bias of manual sensorimotor torque control with the ipsilesional hand following stroke reminiscent of premotor neglect. Both intact finger force-to-position coordination and visuomotor control may compensate for the spatial sensorimotor bias in most stroke patients. Future studies will have to confirm the found bias and evaluate the association with premotor neglect.

Ipsilateral hand impairment predicts long-term outcome in patients with subacute stroke

BACKGROUND

Ipsilateral hand (ILH) impairment is documented following motor stroke, but its impact on long-term outcome remains unknown. We assessed ILH impairment in subacute stroke and tested whether ILH impairment predicted long-term outcome.

METHODS

We performed a longitudinal study in 209 consecutive patients with unilateral stroke and sensorimotor deficit at admission. ILH impairment was evaluated using Purdue Pegboard Test (PPT) and handgrip strength and defined as mild (z-score <-1) or moderate (z-score <-1.65). We used logistic regression (LR) to predict outcome assessed 9 (7-12) months post-stroke with the modified Rankin scale (mRS) categorized into good (mRS≤1) and poor outcome (mRS≥2). For internal validation, LR-bootstrapping, and cross-validation with Lasso and Random-Forest were performed.

RESULTS

ILH impairment assessed at 89.04 ±45.82 days post-stroke was moderate in 10.53% (95% CI, 6.7, 14.83) for PPT and 17.22% (95% CI, 11.96, 22.49) for grip, and mild in 21.05% (95% CI, 15.78, 26.79) for PPT and 35.89 (95% CI, 29.67, 42.58) for grip. Good outcome was predicted by ILH-PPT (B=1.03 [95% CI, 0.39, 3.31]), ILH-grip (B=1.16 [95% CI, 0.54, 3.53]), low NIHSS-discharge (B=-1.57, [95% CI, -4.0, -1.19]), and no depression (B=-0.62, [95% CI, -1.63, -0.43]), accounting for stroke delay (B=-0.011, [95% CI, -0.06, 0.01]). Model efficiency was 91.6% (AUC=0.977, 95%CI, 0.959, 0.996). Lasso and Random-Forest methods provided similar results, confirming the LR model robustness.

CONCLUSIONS

ILH impairment is frequent after motor stroke and predicts long-term outcome. We propose to integrate ILH impairment in rehabilitation programs to improve recovery and serve research interventions such as neuromodulation.

Neural Control of Stopping and Stabilizing the Arm

Stopping is a crucial yet under-studied action for planning and producing meaningful and efficient movements. In this review, we discuss classical human psychophysics studies as well as those using engineered systems that aim to develop models of motor control of the upper limb. We present evidence for a hybrid model of motor control, which has an evolutionary advantage due to division of labor between cerebral hemispheres. Stopping is a fundamental aspect of movement that deserves more attention in research than it currently receives. Such research may provide a basis for understanding arm stabilization deficits that can occur following central nervous system (CNS) damage.