Article Figures & Data
Figures
- Figure 1.
Experimental setup and data from representative subjects. A, Experimental setup. Subjects held the handle of a robot manipulandum and viewed the image projected on a screen that covered both their limb and the robot. The subjects performed a shooting movement (quick reaching out) to go through a target at 45° and hit a virtual pillow. The white dot at center indicates their start position. The white arc (radius, 10 cm, centered at the start position) indicates the boundary of the task space. As the hand crossed the arc, the robot produced a virtual pillow and assisted in bringing the hand back to center. During targeted reaching, the arc was not visible. B, Time course of the experiment. Localization task is explained in C. Generalization task involved reaching to targets other than the trained target at 45°. The adaptation phase includes 220 trials in which a perturbation was gradually imposed on the relationship between hand motion and cursor motion. C, In the localization task, without being given an explicit target, the subjects made a reach to cross the arc without any form of visual feedback. After the robot brought the hand back to the start position, subjects pointed with their left hand to the remembered location of their right hand as it crossed the arc in the previous trial. The arc is displayed only in the localization task. D, Baseline performance in the localization task. Localization error is the difference between estimated hand position at the end of the reach and actual hand position. E, Baseline performance in the generalization task. Reach error is the difference between reach angle and target angle. The movements were attracted toward the 45° target, the target for which the movements were repeated. F, Data from a representative control subject. The result of a reach in the localization task is shown for the baseline condition. The red filled circle is actual reach angle and the open blue circle is the reported angle (reach percept). During the training phase, a target was displayed at 45° and a visual rotation was gradually imposed. The gray region represents reach angle for which the cursor would strike the target area. The red trace represents actual reach angle. The three large spikes reflect set breaks. The result of a reach in the postadaptation localization task is shown in the final column. The hand reached toward 15° but the subject reported the hand at near 40°. G, Data from a representative cerebellar subject (CBL). Format is the same as in F.
- Figure 2.
Group performance during training. A, Reach direction over trials during the training. The data points are the average (±SEM) of the reach angle across subjects. The gray area indicates reach region for which the cursor would strike the target. B, Change in reach angle from the first five trials to the last five trials of training (immediately before generalization task). The two groups displayed comparable change in their motor commands. C, Change in reach angle from the trial before to the trial after the set break. Cerebellar subjects (CBL) exhibited greater forgetting.
- Figure 3.
Estimating the change in the inverse and forward models in the control and cerebellar (CBL) groups. A, Performance in the generalization task in the baseline (dashed line) and postadaptation (solid line) conditions. The colored regions represent the within-group change in performance. Error bars are SEM. B, Within-subject change in reach angle from the baseline to the postadaptation condition in the generalization task (a proxy for the change in the inverse model). Error bars are SEM. C, Results of fitting a cosine function (Eq. 2) to the data in the generalization task. The bar graphs are parameters of the fit. Shaded regions and error bars are 95% confidence intervals. D, Performance in the localization task in the baseline (dashed line) and postadaptation (solid line, representing the first five trials) conditions. The colored regions are the within-group change in performance. The y-axis is the reported reach angle. Error bars are SEM. E, Within-subject change in reach percept in the localization task (a proxy for the forward model). Error bars are SEM. F, Fit of a cosine function (Eq. 1) to the data in the localization task. The bar graphs (right) are parameters of the fit. The peak magnitude, center location, and decay rate were all significantly different between the two groups. The cosine function (left) represents the change in the forward model, as evaluated at the first localization trial, with respect to baseline. G, Distribution of reach directions in the control and cerebellar groups during the localization task. The plot shows the probability of reach angle (bin size, 10°). H, Time course of change in reach percept as a function of trial in the postadaptation localization trials. The plots are generated from a fitted model (Eq. 1).
- Figure 4.
Performance of individual subjects. A, Average change in reach percept for each subject, plotted against that subject's change in reach direction during adaptation training. The x-axis is the same measure as in Figure 2B, i.e., change in reach angle from the first five trials to the last five trials of training (immediately before localization task). The y-axis is the change in reach percept for each subject (localization task, postadaptation period with respect to preadaptation), averaged over reaches made between 15° and 55°. Blue circles represent healthy controls; red circles represent cerebellar patients. The number next to each circle identifies that cerebellar subject in Table 1. B, Change in reach direction during adaptation training is plotted against that subject's ataxia score. The y-axis is the same measure as in Figure 2B, i.e., change in reach angle from the first five trials to the last five trials of training. Generally, the subjects who were more impaired in their clinical score also exhibited less adaptation. C, Change in reach angle from the baseline to the postadaptation condition in the generalization task, as measured for reaches to the main target (at 45°), is plotted for each subject against that subject's ataxia score.
- Figure 5.
Simulation results. A, The simulated adaptive system was trained on a perturbation protocol similar to the one experienced by the subjects. B, State of the forward model in trials 1, 21, 41, etc. Red line is the state at baseline; dark blue line is the state at end of training. With increased trials, the peak shifts to smaller reach angles. Superimposed on the simulation data are data from control subjects in the localization task (Fig. 3D). C, Change in the forward model with respect to baseline. The black line is data from control subjects in the localization task (Fig. 3E). D, Reach angle as a function of target direction. The colored lines represent state of the inverse model (Eq. 6) in trials 1, 21, 41, etc. Red line is the state at baseline; dark blue line is the state at end of training. With increased trials, the generalization narrows for larger target angles. Superimposed on the simulation data are data from control subjects in the generalization task (Fig. 3A). Arrow indicates the trained target direction (45°). E, Change in the inverse model with respect to baseline. The black line is data from control subjects (Fig. 3B).
Tables
Identifier Gender Age (years) Handedness Diagnosis ICARS 1 M 37 L SCA8 46 2 M 54 R SCA6 and SCA8 63 3 F 67 R Autosomal dominant 55 4 F 67 R SCA6 5 5 M 75 R R PICA and R SCA stroke 17 6 F 65 R Sporadic 35 7 M 47 R Sporadic 51 8 F 57 R SCA6 33 9 F 52 R SCA6 23 ADCA, autosomal dominant ataxia.
