The Efficiency, Efficacy, and Retention of Task Practice in Chronic Stroke

Abstract

In motor skill learning, larger doses of practice lead to greater efficacy of practice, lower efficiency of practice, and better long-term retention. Whether such learning principles apply to motor practice after stroke is unclear. Here, we developed novel mixed-effects models of the change in the perceived quality of arm movements during and following task practice. The models were fitted to data from a recent randomized controlled trial of the effect of dose of task practice in chronic stroke. Analysis of the models' learning and retention rates demonstrated an increase in efficacy of practice with greater doses, a decrease in efficiency of practice with both additional dosages and additional bouts of training, and fast initial decay following practice. Two additional effects modulated retention: a positive "self-practice" effect, and a negative effect of dose. Our results further suggest that for patients with sufficient arm use post-practice, self-practice will further improve use.

Keywords: chronic stroke; dose; mixed effect models; motor learning; neurorehabilitation; retention.

Figure 1:

Schematics of the schedules of task practice and MAL assessments in DOSE. A. Timing of motor practice based on the train-wait-train paradigm, in which three 1-week bouts of practice are separated by 1-month “wait” periods. B. Example of a simulation showing the changes in perceived quality of arm movements in the train-wait-train paradigm modeled with a piece-wise linear model with a positive retention parameter (see Equation 1). The black dots show the timing of each assessment over the 37 weeks of the DOSE trial.

Figure 2:

Quality of movement as measured by the MAL over the 37 weeks of the DOSE trial, assessed before, during, between, and following the three practice bouts, and an example of model fit to the data, using the best fitting model (Model 7, Table 1). A. Data (dots) and model fit (lines) for all 41 participants. Gray vertical lines show the three week-long practice bouts. Note the overall excellent fit of the model to all participants (except for 2^nd participant in 30-hour dose, who exhibited large MAL variability). B. Individual models re-arranged by nominal dosages. Note the following: 1) Larger increase in MAL during practice for larger dosages (increased dose efficacy); 2) Diminishing returns for larger dosages (decreased dose efficiency); 3) Diminishing returns for more practice weeks (decreased practice bout efficiency); 4) Decrease in MAL post-practice for larger dosages; 5) Further increase in MAL for high average post-practice MAL; and 6) in 0 dosage group, increase in MAL. These observations were all confirmed statistically – see text.

Figure 3:

Fixed effect parameters used to test all six hypotheses. A. Effect of dose on the MAL during supervised practice (dose efficacy; Models 1, Table 1). B. Effect of increasing the dose on gain in MAL per hour of practice (dose efficiency; Models 2; the empty circle above the data point in 30-hour group corresponds to the categorical model parameter after removing 3 participants with an initial MAL > 3, see results). C. Effect of increasing the number of weeks of formal practice on gain in MAL per hour (duration efficiency; Models 3). D. Effect of time on retention: Retention rate in the 6 months following supervised practice as a function of months post-practice (0-1 months, 2-3 months, and 3 to 5 months) (Model 4). E. Effect of dose on retention (Models 5). F. Effect of average post-practice MAL on gain in MAL (Models 6). The thick dark line shows retention as a function of average post-practice MAL in Model 6.1. The colored lines show retention as a function of average post MAL for different doses and the colored dots show the individual retention rates (mixed effects) in Model 6.2.