Learning to never forget—time scales and specificity of long-term memory of a motor skill

Abstract

Despite anecdotal reports that humans retain acquired motor skills for many years, if not a lifetime, long-term memory of motor skills has received little attention. While numerous neuroimaging studies showed practice-induced cortical plasticity, the behavioral correlates, what is retained and also what is forgotten, are little understood. This longitudinal case study on four subjects presents detailed kinematic analyses of humans practicing a bimanual polyrhythmic task over 2 months with retention tests after 6 months and, for two subjects, after 8 years. Results showed that individuals not only retained the task, but also reproduced their individual “style” of performance, even after 8 years. During practice, variables such as the two hands' frequency ratio and relative phase, changed at different rates, indicative of multiple time scales of neural processes. Frequency leakage across hands, reflecting intermanual crosstalk, attenuated at a significantly slower rate and was the only variable not maintained after 8 years. Complementing recent findings on neuroplasticity in gray and white matter, our study presents new behavioral evidence that highlights the multi-scale process of practice-induced changes and its remarkable persistence. Results suggest that motor memory may comprise not only higher-level task variables but also individual kinematic signatures.

Robust retention of individual sensorimotor skill after self-guided practice

“…These results are consistent with previous findings by Park et al (2013) who reported retention of spatiotemporal patterns not only after 6 mo, but also after 8 yr. However, due to the longitudinal nature of this previous experiment, results from only four subjects were reported with two cases for the 8-yr retention.…”

“…This result corroborates the previous case study, where subjects acquired a 3:1 pattern without any feedback (Park et al 2013). This previous experiment also highlighted the presence of several time scales in different variables, which was again seen in the present study.…”

“…Nevertheless, this self-guided training is also successful. A recent longitudinal case study on the acquisition of a polyrhythmic bimanual task first demonstrated that practice without any quantitative feedback could lead to stable retention not only after 6 mo, but also after 8 yr (Park et al 2013). The present study uses a larger cohort of subjects that practices a slightly modified task to corroborate the observed kinematic specificity of retention.…”

“…Aside from isolated studies that reported relatively gross behavioral measures, usually on very few subjects, there have been only few studies that assessed retention after more than a few days or weeks (Adams 1987;Dayan and Cohen 2011;Nourrit-Lucas et al 2013;Park et al 2013;Romano et al 2010;Swift 1910). Even less attention has been given to practice conditions that may facilitate robust long-term retention and, thereby, ensure stable neuroplastic changes.…”

“…To obtain the continuous movement frequencies of the two hands and their ratio, the two arms' position data were transformed into instantaneous phase using the Hilbert transform (Park et al 2013;Pikovsky et al 2003). Figure 2, A and B, shows two trial segments early and late in practice with different degrees of regularity in period, amplitude, and relative phase.…”