Amplified Intraindividual Variability in Motor Performance in Stroke Survivors: Links to Cognitive and Clinical Outcomes

Abstract

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.

Keywords: cognitive function; consistency; goal‐directed movements.

FIGURE 1

Goal‐directed task. (A) Schematic representation of the set‐up showing the position of the foot. (B) Representative goal‐directed performance. Participants were required to match a force target of 10 N in 180 ms. The relative distance from the origin to peak of the bell‐shaped performance represents the endpoint. Intraindividual variability (IIV) in motor performance represents the trial‐to‐trial inconsistency in endpoint.

FIGURE 2

Intraindividual variability (IIV) in motor performance between stroke survivors and healthy older adults (HOA). (A) Representative endpoint residual T‐scores (purified for group and trial) across the 30 trials for a stroke and healthy older adult participant. IIV in motor performance is represented by the greater variation in endpoint across trials for the stroke participants relative to the healthy older adult participant. (B) At the cohort level, stroke survivors exhibited significantly greater IIV in motor performance than healthy older adults.

FIGURE 3

Multiple linear regression model predicts intraindividual variability (IIV) in motor performance from domain‐specific cognition. Deterioration in executive function, processing speed, visuospatial processing, and episodic memory predicted IIV in motor performance in stroke survivors.

FIGURE 4

Multiple linear regression predicts intraindividual variability (IIV) in motor performance from global assessments. The years of education, Dementia Rating Scale‐2 (DRS‐2), Modified Rankin Scale (mRS), and ankle strength predicted IIV in motor performance in stroke survivors.