Corticomotor plasticity induced by tongue-task training: a longitudinal fMRI study

Objectives: Corticomotor pathways may undergo plastic changes in response to acquisition of new motor skills. Little is known about the control of tongue musculature. The aim was to determine the effect of a novel tongue-task training on corticomotor pathways. Methods: Eight healthy, right-handed men performed standardized tongue protrusion onto a force transducer. The training task consisted of a relax-protrude-hold-relax cycle with 1.0 N as the target at the hold phase lasting for 1.5 s. Subjects repeated this task for 1 hour (in total 288 protrusion cycles). Blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD-fMRI) during tongue protrusion and right finger tapping (1 Hz repetition) were measured at baseline (before tongue training), 1-hour after tongue training, one-day and one-week follow-up. Results: In the baseline condition, tongue protrusion produced increased BOLD-fMRI signals in bilateral central sulcus / precentral gyrus and right medial frontal gyrus (P<0.001) whereas finger tapping caused activity in left central sulcus / precentral gyrus, lentiform nucleus, claustrum, bilateral medial frontal / superior frontal gyri, and right cerebellum (P<0.001) compared to rest. All subjects completed the tongue-protrusion task (mean success rate 34.1 ± 4.8%). Immediately after tongue training, BOLD-fMRI signals showed a decreased activity in medial frontal gyrus and in right premotor area during tongue protrusion compared with baseline (P=0.006). Right finger tapping, however, also caused a decrease in right medial and superior frontal gyrus (P=0.001). No BOLD-fMRI effects could be detected after one-day or one-week compared to baseline. Conclusion: The results verified the involvement of specific corticomotor areas associated with tongue protrusion and finger tapping. However, this study suggests that acquisition of new motor skills, such as the tongue training, may not lead to longer-lasting changes detectable with the BOLD-fMRI technique.