Cortical enhancement of posture and movement planning, initiation, and execution during standing voluntary reach following stroke

Abstract

Stroke is the leading cause of disability that frequently includes impairments of postural control and upper extremity function. The ability to maintain balance while performing reaching during everyday activities requires appropriate sequencing of anticipatory postural adjustments (APAs) and the goal-directed reaching movement. Although studies have shown that these abilities are frequently compromised following stroke, the interaction of posture and upper extremity movement coupling (APA-reach sequence) regarding movement planning, preparation, and execution is not well understood. We investigated posture and movement planning, preparation, and execution in individuals with chronic hemiparesis and healthy controls. Movement planning and preparation of APA-reach sequence were examined by StartReact (SR) responses elicited by a loud acoustic stimulus (LAS). After an instructed delayed period, subjects performed a standing reaching task in response to a "go" light cue. An LAS was randomly delivered at - 500, - 200, and 0ms relative to the "go" cue. Kinetic, kinematic, and electromyography data were recorded to characterize APA-reach movement response. Subjects with stroke demonstrated a marked reduction in the occurrence of the SR responses and impaired APA-reach performance during not only the paretic but also the nonparetic arm reaching compared to healthy controls. This indicates that the deficits in posture and movement planning, preparation, and execution are not specific to the lesioned side only but system-wide to both the lesioned and contralesional sides. Moreover, compensation strategy characterized by greater involvement of trunk and pelvic rotation was utilized during the paretic arm reaching compared to the nonparetic arm reaching and healthy controls. Lastly, we tested how transcranial direct current stimulation (tDCS) applied over the region of premotor areas and primary motor cortex (M1) affect movement planning and preparation of a standing reaching task in individuals with stroke and healthy subjects. The main finding was that stroke-related deficits in movement planning and preparation as shown by an abnormal absence of SR responses during the paretic arm reaching could be improved by application of anodal tDCS over the region of lesioned M1 and the enhancement effects are depending on the timing of the LAS.