Training-induced cortical plasticity compared between three tongue-training paradigms

The primary aim of this study was to investigate the effect of different training types and secondary to test gender differences on the training-related cortical plasticity induced by three different tongue-training paradigms: (1) therapeutic tongue exercises (TTE), (2) playing computer games with the tongue using the Tongue Drive System (TDS) and (3) tongue-protrusion task (TPT). Forty-eight participants were randomized into three groups with 1 h of TTE, TDS, or TPT. Stimulus-response curves of motor evoked potentials (MEPs) and motor cortex mapping for tongue muscles and first dorsal interosseous (FDI) (control) were established using transcranial magnetic stimulation at three time-points: (1) before tongue-training, (2) immediately after training, (3) 1 h after training. Subject-based reports of motivation, fun, pain and fatigue were evaluated on 0-10 numerical rating scales after training. The resting motor thresholds of tongue MEPs were lowered by training with TDS and TPT (P < 0.011) but not by TTE (P = 0.167). Tongue MEP amplitudes increased after training with TDS and TPT (P < 0.030) but not with TTE (P = 0.302). Men had higher MEPs than women in the TDS group (P < 0.045) at all time-points. No significant effect of tongue-training on FDI MEPs was observed (P > 0.335). The tongue cortical motor map areas were not significantly increased by training (P > 0.142). Training with TDS was most motivating and fun (P < 0.001) and TTE was rated the most painful (P < 0.001). Fatigue level was not different between groups (P > 0.071). These findings suggest a differential effect of tongue-training paradigms on training-induced cortical plasticity and subject-based scores of fun, motivation and pain in healthy participants.