Hemispheric specialization for movement control produces dissociable differences in online corrections after stroke

Abstract

In this study, we examine whether corrections made during an ongoing movement are differentially affected by left hemisphere damage (LHD) and right hemisphere damage (RHD). Our hypothesis of motor lateralization proposes that control mechanisms specialized to the right hemisphere rely largely on online processes, while the left hemisphere primarily utilizes predictive mechanisms to specify optimal coordination patterns. We therefore predict that RHD, but not LHD, should impair online correction when task goals are unexpectedly changed. Fourteen stroke subjects (7 LHD, 7 RHD) and 14 healthy controls reached to 1 of the 3 targets that unexpectedly "jumped" during movement onset. RHD subjects showed a considerable delay in initiating the corrective response relative to controls and LHD subjects. However, both stroke groups made large final position errors on the target jump trials. Position deficits following LHD were associated with poor intersegmental coordination, while RHD subjects had difficulty terminating their movements appropriately. These findings confirm that RHD, but not LHD, produces a deficit in the timing of online corrections and also indicate that both stroke groups show position deficits that are related to the specialization of their damaged hemisphere. Further research is needed to identify specific neural circuits within each hemisphere critical for these processes.

Figure 1.

Overlap of lesion location in the LHD and RHD groups. Colors of shaded regions denote percentage of LHD and RHD subjects with lesions in the corresponding region.

Figure 2.

(A) Side and top view of experimental apparatus are shown. (B) Baseline and (C) target jump locations in the lateral, center, or medial direction relative to the starting position. All targets were presented in the ipsilateral hemispace relative to the arm. (D) Schematic of computation for corrective interaction torque (x-axis = time). Calculated interaction torque is on the left. Arrow indicates full-wave rectification; dashed line indicates correction time; asterisk indicates value of peak corrective interaction torque.

Figure 3.

Baseline performance. Mean (A) movement time, (B) peak tangential velocity, and (C) final position error for each target (Lat, lateral; Cen, center; and Med, medial location in ipsilesional hemispace) is displayed for the left and right arms of healthy control groups (LHC, RHC; solid line) and the ipsilesional arms of LHD and RHD groups (dashed line). Error bars indicate standard error.

Figure 4.

Target jump performance. (A) Top view of handpaths for all target jump trials for individual HC and HD subjects. Mean (B) movement time and (C) final position error for each target (Lat–Cen, lateral to center; Cen–Med, center to medial; Cen–Lat, center to lateral; Med–Cen, medial to center) is displayed for the left and right arms of healthy control groups (LHC, RHC; solid line) and the ipsilesional arms of LHD and RHD groups (dashed line). Error bars indicate standard error.

Figure 5.

Target jump performance. (A) Mean correction time (% baseline movement time) is displayed for the left and right arms of healthy control groups (LHC, RHC) and the ipsilesional arms of LHD and RHD groups. Error bars indicate standard error. (B) Tangential velocity profiles from individual baseline trials (thin line) to the center location (Cen) and target jump trials (thick line), when the target jumped from the center location to the medial location (Cen–Med), are shown for individual HC and HD subjects. Arrows indicate correction time for target jump trials.

Figure 6.

(A) Torque profiles are shown for shoulder net torque (gray line), elbow net torque (thick black line), elbow muscle torque (thin black line), and elbow interaction torque (dashed line) during the individual target jump trials shown in Figure 5B for the LHD subject (left panel) and RHD subject (right panel). Corresponding handpaths are inset. Arrows indicate correction time. (B) Final position error of each target jump trial is plotted as a function of corrective interaction torque for an LHD and RHD subject, with corresponding Pearson r value. (C) Mean normalized Pearson r (Fisher z-score) of final position error versus corrective interaction torque is displayed for the left and right arms of healthy control groups (HC) and the ipsilesional arms of LHD and RHD groups (HD). Bars indicate standard error of mean. *Tukey's test: P < 0.05.