Reward and punishment enhance motor adaptation in stroke

Abstract

Word count: 3492 2 ABSTRACTThe effects of motor learning, such as motor adaptation, in stroke rehabilitation are often transient, thus mandating approaches that enhance the amount of learning and retention. Previously, we showed in young individuals that reward-and punishment-feedback have dissociable effects on motor adaptation, with punishment improving adaptation and reward enhancing retention. If these findings were able to generalise to stroke patients, they would provide a way to optimize motor learning in these patients. Therefore, we tested this in 45 chronic stroke patients allocated in three groups. Patients performed reaching movements with their paretic arm with a robotic manipulandum. After training (day 1), day 2 involved adapting to a novel force-field. During this adaptation phase, patients received performance-based feedback according to the group they were allocated: reward, punishment or no feedback (neutral). On day 3, patients readapted to the forcefield but all groups now received neutral feedback. All patients adapted, with reward and punishment groups displaying greater adaptation and readaptation than the neutral group, irrespective of demographic, cognitive or functional differences. Remarkably, the reward and punishment groups adapted to similar degree as healthy controls. Finally, the reward group showed greater retention. This study provides, for the first time, evidence that reward and punishment can enhance motor adaptation in stroke patients. Further research on reinforcement-based motor learning regimes is warranted to translate these promising results into clinical practice and improve motor rehabilitation outcomes in stroke patients.

Reward-based improvements in motor control are driven by multiple error-reducing mechanisms

“…For instance, the stretch reflex is sensitive to cognitive factors such as postural threat (standing next to a signficant height; Horslen et al, 2018). Nevertheless, the contribution of stiffness in reward-based performance has implications for current lines of research on clinical rehabilitation that focus on improving rehabilitation procedures using reward (Goodman et al, 2014; Quattrocchi et al, 2017). While several studies report promising improvements, excessive stiffness may expose vulnerable clinical populations to increased risk of fatigue and even injury.…”

“…However, it is currently unclear whether this generalizes to more complex reaching movements. As the use of reward has generated much interest as a potential tool to enhance rehabilitation procedures for clinical populations (Goodman et al, 2014; Quattrocchi et al, 2017), it is crucial to determine whether reward can improve the selection and execution components of a reaching movement without interference.…”

Intention to learn modulates the impact of reward and punishment on sequence learning

“…Although it should be noted that visuomotor adaptation is generally considered to be a separate process from motor-sequence learning, complementary evidence comes from the visuomotor adaptation literature. Similar to prior work in sequence learning 5,13 , prior work using motor adaptation tasks have found that reward benefits retention, while punishment benefits performance during training 11,[21][22][23] . For example, it has been found that the beneficial effects of reward-feedback to retention in visuomotor adaptation tasks appear to depend on explicit processes, and a distractor-task that disrupts explicit processes completely abolishes learning when participants must use reward-based feedback to adapt 21,24,25 .…”

“…This possibility may be interesting to explore in the future using patients with medial temporal lobectomy 41 . Reward and punishment did not impact immediate retention Reward did not benefit performance on the immediate retention probes in the intentional or the unintentional learning conditions, which effectively replicates the similar null result found in prior work by our group 6 . Given the widely observed benefit of reward to visuomotor adaptation memory retention, it will be important to understand whether any specific conditions reliably foster reward-related memory benefits in the context of motor skill learning 4,11,22,23 .…”

The carrot and the stick seem to enhance motor learning in patients with stroke

“…Identifying novel approaches to address their impairments is an important challenge. In their  JNNP  paper, Quattrocchi et al  show that both reward-based and punishment-based feedbacks enhance the rate of motor learning following stroke2. Patients who trained with this additional feedback learnt to adapt their movements to counteract a robot-induced force field faster than those who received neutral feedback.…”