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Vaalto S, Julkunen P, Säisänen L, Könönen M, Määttä S, Karhu J (2013) Long-term plasticity may be manifested as reduction or expansion of cortical representations of actively used muscles in motor skill specialists. NeuroReport, 24(11):596-600    
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Abstract
Our aim was to study long-term plasticity in the organization of cortical muscle representations due to extensive motor training for different skills. We were especially interested in whether skill-specific demands on independent hand muscle movements and synchronous leg muscle movements are reflected differently in the reorganization of muscle representations. We used navigated transcranial magnetic stimulation to estimate the size of cortical representations of opponens pollicis, abductor digiti minimi, and tibialis anterior muscles in five string instrument players, five figure skaters, and five controls. The extent of the representation area was presented as an amplitude-area curve showing the spatial distribution of motor evoked potentials. The size of representation areas was compared between the dominant and nondominant hemispheres and between the groups. The representation area of the left abductor digiti minimi (critical for reaching right tones) in the right, nondominant hemisphere was smaller in string players and the representation area of the tibialis anterior in the dominant hemisphere (critical for jumps) was larger in figure skaters when compared with controls. Reorganization in the motor cortex may differ depending upon the skill and an individual muscle’s role in the skill. A smaller representation area of the independently used hand muscle in masters of fine motor skills may reflect long-term plasticity toward more focused representation, which may be beneficial in accurate and discrete cortical control of the muscle. Larger cortical representations are related to skill demanding coactivation of proximal and distal lower limb muscles