Perceptuo-motor planning during functional reaching after stroke

Abstract

In healthy young adults, reaching movements are planned such that the initial grasp position on the object is modulated based on the final task goal. This perceptuo-motor coupling has been described as the end-state comfort effect. This study aimed to determine the extent to which visuo-perceptual and motor deficits, but not neglect, due to stroke impact end-state comfort measured as the grasp-height effect. Thirty-four older adults (17 controls, 17 chronic stroke) performed a functional goal-directed two-sequence task with each arm, consisting of reaching and moving a cylindrical object (drain plunger) from an initial to four target platform heights, standardized to body height, in a block randomized sequence. Arm motor impairment (Fugl-Meyer Assessment) and visual-perceptual deficits (Motor-Free Visual Perception Test) were assessed in stroke subjects, and arm and trunk kinematics were assessed in all subjects. The primary outcome measure of the grasp-height effect was the relationship between the grasp heights used at the home position and the final target platform heights. Mixed model analysis was used for data analysis. The grasp-height effect was present in all participants, but decreased in stroke subjects with visuo-perceptual impairments compared to controls. In stroke subjects with sensorimotor impairments alone, indicated by altered kinematics, the grasp-height effect was comparable to controls. This first study examining the grasp-height effect in individuals with stroke provides new knowledge of the impact of visuo-perceptual deficits on movement planning and execution, which may assist clinicians in selecting more effective treatment strategies to improve perceptuo-motor skills and enhance motor recovery.

Keywords: Anticipatory motor planning; Arm; End-state comfort effect; Kinematics; Stroke; Visual perception.

Fig. 1

The task incorporated reaching, grasping and moving an object with a vertical wooden shaft (drain plunger) from a “home platform” to four target platforms of different heights (% of body height). The task was repeated in blocks of ten trials per target with the order of target height and starting side randomized across subjects

Fig. 2

Histograms of mean (SD) kinematic variables of the reach-to-move task for the stroke group, the stroke subgroup with no visuo-perceptual impairments (no VPI), the stroke subgroup with visuo-perceptual impairments (VPI) and the left arm of the healthy control subjects. Movement time of reaching, arm and trunk angle position data at the end of the reach phase are shown. Full elbow extension and horizontal arm abduction laterally in line with the shoulders were defined as 0°. *p < 0.05 compared to healthy controls

Fig. 3

Linear relationships, plotted as slopes, of grasp height values for 35 and 70% target platform heights for a the less-affected (n = 17) and affected (n = 17) arms of subjects with stroke, and for b subgroups of stroke subjects with (VPI, n = 7) and without visuo-perceptual impairment (no VPI, n = 10) together with the left arm of healthy controls (control, n = 17). Significant differences between stroke groups/subgroups compared to controls are indicated