Amplified Intraindividual Variability in Motor Performance in Stroke Survivors: Links to Cognitive and Clinical
Stefan Delmas1, Anjali Tiwari1, Han-Yun Tseng2
1Department of Health and Exercise Science, Colorado State University, Fort Collins, Colorado, USA.
Background:
Intraindividual variability (IIV) in motor performance reflects unintentional fluctuations in the motor output across repeated attempts. Behavioral variability in older adults has been linked to impaired neuronal integrity and cognitive decline. Despite this, the traditional motor assessments in stroke have neglected to characterize IIV in motor performance also known as "motor inconsistency." Therefore, the aim of this study was to investigate the impact of stroke on motor inconsistency and its relationship with cognitive and clinical outcomes.
Methods:
Sixty-six stroke survivors and 32 healthy older adults performed 30 trials of a goal-directed task to match a force-time target of 10 N in 180 ms. To measure motor inconsistency, we applied a well-established approach to measuring IIV from the cognitive aging literature that accounts for the inherent, systematic effects of practice and mean-level performance on IIV. In addition, participants completed domain-specific cognitive evaluations and global clinical assessments. Domain-specific cognitive evaluations assessed episodic memory, visuospatial processing, processing speed, and executive function. Global clinical assessments included years of education as a proxy of cognitive reserve, the Dementia Rating Scale-2 (DRS-2), ankle strength, and the Modified Rankin Score (mRS).
Results:
Stroke survivors exhibited greater motor inconsistency compared with healthy older adults. Declines in domain-specific cognitive function, particularly executive dysfunction, predicted motor inconsistency in stroke survivors. Cognitive reserve and mRS emerged as significant predictors of motor inconsistency.
Conclusions:
Stroke significantly impairs the ability to perform a motor task with consistency. Compromised executive function following stroke is associated with increased motor inconsistency. Interestingly, reduced cognitive reserve and greater functional disability are linked to increased motor inconsistency in stroke survivors. These findings highlight that inconsistency is an important indicator of motor dysfunction following stroke that is linked to cognitive and clinical outcomes and may serve as an important target for stroke rehabilitation.
