Deficits in motor abilities for multi-finger force control in hemiparetic stroke survivors

Abstract

The ability to control redundant motor effectors is one of hallmarks in human motor control, and the topic has been studied extensively over several decades since the initial inquiries proposed by Nicholi Bernstein. However, our understanding of the influence of stroke on the control of redundant motor systems is very limited. This study aimed to investigate the effect of stroke-related constraints on multi-finger force control abilities in a visuomotor task. Impaired (IH) and less-impaired hands (LH) of 19 hemiparetic stroke survivors and 19 age-matched control subjects were examined. Each hand repeatedly produced isometric forces to match a target force of 5 N shown on a computer screen using all four fingers. The hierarchical variability decomposition (HVD) model was used to separate force-matching errors (motor performance) into task-relevant measures (accuracy, steadiness, and reproducibility). Task-irrelevant sources of variability in individual finger force profiles within and between trials (flexibility and multiformity) were also quantified. The IH in the stroke survivors showed deficits in motor performance attributed mainly to lower accuracy and reproducibility as compared to control hands (p < 0.05). The LH in stroke survivors showed lower reproducibility and both hands in stroke also had higher multiformity than the control hands (p < 0.05). The findings from our HVD model suggest that accuracy, reproducibility, and multiformity were mainly impaired during force-matching task in the stroke survivors. The specific motor deficits identified through the HVD model with the new conceptual framework may be considered as critical factors for scientific investigation on stroke and evidence-based rehabilitation of this population.

Novel Methods to Enhance Precision and Reliability in Muscle Synergy Identification during Walking

“…Either way, high variability of muscle synergies warrants further exploration, especially when applying synergy analyses to individuals with brain injury, because such variability across repetitions of the same movement could be interpreted as a challenge to the synergy hypothesis which postulates that synergies represent a fixed modular pattern of motor activities in purposeful behavior ( Ivanenko et al, 2006 ; Bizzi and Cheung, 2013 ). Increased motor variability across trials is often observed in patients with brain injuries ( Kim et al, 2016 ) or older adults ( Lovden et al, 2007 ). Moreover, muscle activity patterns can vary owing to changes in sensory input and subcortical reflexes ( Sinkjaer et al, 2000 ; Kim et al, 2013 ).…”

Strength or Motor Control: What Matters in High-Functioning Stroke?

“…Despite extensive research on the association between strength and motor function in stroke survivors, the evidence regarding role of impaired motor control on functional capacity is sparse, especially for the lower-limb (13, 14). A study on the upper-limb motor control demonstrated that increased variability and reduced accuracy for finger forces was related to poor functional outcome during grasp and release in stroke (15). The influence of strength and motor control on functional capacity potentially varies with the severity of stroke motor impairments.…”

Stroke Leads to Abnormal Coordination of the Multiple Upper Extremity Joints During Passive Movement

“…In previous stroke studies, coordination patterns during voluntary movements were not consistent, reporting unchanged IC [18,40], decreased IC [41], and increased IC [20], along with unchanged TIV [18,40], and greater TIV [19,20]. However, TRV was found to be greater than in control [19,20,41]. The previous studies suggested that this unexpected finding might have resulted from large inherent variability of neural signals between motor cortex and effectors [42] or being more dependency of effectors in the patients with stroke [43].…”

“…In a person with neurological diseases such as Parkinson's disease [14], olivoponto-cerebellar atrophy [15], multiple sclerosis [16] and spinocerebellar degeneration [17], different patterns of motor synergies have been observed often with decreased TIV and increased TRV as compared to healthy groups. However, previous stroke studies have reported inconsistent results on TRV and TIV between stroke group and healthy group during a UE reaching task [18][19][20]. One of the possibilities for the inconsistent results may be attributed to changes in passive properties of UE after stroke.…”