Acute pain impairs retention of locomotor learning, regardless of the context of retention testing

Our group and others have shown that the presence of an acute painful stimulus may interfere with retention of motor learning. Conversely, other evidence suggests this effect may not be truly due to pain, but due to a change in context when testing retention, i.e., testing retention in a nonpainful context when learning occurred in a painful context. Yet to our knowledge, no study has directly compared the retention of learning acquired under painful conditions with versus without a context change. To answer this question, we tested 30 young, healthy adults on a locomotor learning and retention paradigm. All participants walked on a treadmill with a monitor displaying distorted real-time visual feedback of step lengths to induce learning of an asymmetric stepping pattern. Retention was assessed 24 h later. Participants were randomized into one of three groups: one received no intervention; one received a painful stimulus during learning on <i>day 1</i> only; and one received the same painful stimulus during both learning on <i>day 1</i> and retention testing on <i>day 2</i>. Pain was induced by applying a combination of topical capsaicin cream and superficial heat to the skin of one leg. We found that while all groups successfully learned the asymmetric pattern, retention was reduced in both groups that experienced pain during learning, regardless of the pain context during retention testing. These findings indicate that pain experienced during the acquisition of a motor skill has a unique and deleterious effect on retention of that motor skill, which could negatively impact rehabilitation efforts.<b>NEW & NOTEWORTHY</b> Here, we show that acute pain experienced during locomotor learning reduces its 24-h retention regardless of the context in which retention is tested. These findings indicate that pain has a deleterious effect on the retention of newly acquired motor skills, possibly impacting the efficacy of motor learning-based rehabilitation interventions for people with painful conditions.