Complex skill learning at a joint initiates competition between its representation in the primary motor cortex (M1) and that of the neighboring untrained joint. This process of representational plasticity has been mapped by cortically-evoking simple movements. We investigated, following skill learning at a joint, 1) whether comparable processes of representational plasticity are observed when mapping is based on volitionally produced complex movements and 2) the consequence on the skill of the adjacent untrained joint. Twenty-four healthy subjects were assigned to either finger- or elbow-skill training or no-training control group. At pretest and posttest, subjects performed complex skill movements at finger, elbow and ankle concurrent with functional magnetic resonance imaging (fMRI) to define learning and allow mapping of corresponding activation-based representations in M1. Skill following both finger- and elbow- training transferred to the ankle (remote joint) (p = 0. 05 and 0. 05); however, finger training did not transfer to the elbow and elbow training did not transfer to the finger. Following finger training, location of the trained finger representation showed a trend (p = 0. 08) for medial shift towards the representation of adjacent untrained elbow joint; the change in intensity of the latter representation was associated with elbow skill (Spearman's ρ = -0. 71, p = 0. 07). Following elbow training, the trained elbow representation and the adjacent untrained finger representation increased their overlap (p = 0. 02), which was associated with finger skill (Spearman's ρ = -0. 83, p = 0. 04). Thus, our pilot study reveals comparable processes of representational plasticity with fMRI mapping of complex skill movements as have been demonstrated with cortically-evoked methods. Importantly, these processes may limit the degree of transfer of skill between trained and adjacent untrained joints. These pilot findings that await confirmation in large-scale studies have significant implications for neuro-rehabilitation. For instance, techniques, such as motor cortical stimulation, that can potentially modulate processes of representational plasticity between trained and adjacent untrained representations, may optimize transfer of skill.
Bibliographical noteFunding Information:
Acknowledgements This work was supported by the University of Minnesota’s Doctoral Dissertation Fellowship to [E. B. P.]; National Center for Research Resources at the National Institutes of Health (grant numbers P41 RR008079, M01-RR00400 to Center for Magnetic Resonance and Research, Minneapolis, MN); National Institutes of Health supporting investigator roles-1K01HD069504 (E. B. P.) and 1 R01 HD 053153-01A2 and 1 RC1 HD063838-01 (J. R. C) and the Program in Physical Therapy at the University of Minnesota. The authors would like to thank Ms. Pooja Arora, Ms. Megan Pline, Ms. Meagan Binenstock, and Dr. Kathleen Anderson for their assistance in data collection and analysis. Also, the authors would like to thank Drs. Theresa Kimberley, James Ashe and Carl Kukulka for valuable feedback.
- Motor cortex
- functional Magnetic Resonance Imaging (fMRI)