Influence of topical anaesthesia on the corticomotor response to tongue training

Objectives: The aim of this experimental study was to investigate if perturbation of somatosensory function would change corticomotor excitability of the tongue musculature in relation to a novel tongue training task. Materials and methods: Sixteen healthy volunteers participated in two randomized and double-blind sessions separated by two weeks, in which topical anaesthetics or placebo cream were applied to the tongue during a standardized tongue training task. Corticomotor excitability was assessed by changes in motor evoked potentials (MEPs) in the tongue musculature evoked by transcranial magnetic stimulation (TMS) before and after training. Results: The success rate of the training task increased in both sessions (relative increase: topical anaesthetics = 53 +/- 53%; placebo = 50 +/- 48%; P = 0.713). The MEP amplitudes increased with stimulation intensity (P < 0.026) in both sessions and there were significantly higher MEP amplitudes on the contralateral tongue muscle compared to the ipsilateral tongue (P < 0.019). There were no differences in MEP amplitudes between the topical anaesthetic and placebo session and there were no main effects of the tongue training task. However, there were significant correlations between increases in success rate and facilitation of the MEP amplitudes in the tongue muscles. Conclusion: Topical anaesthesia has no major effects on corticomotor excitability of tongue musculature and there appears to be a strong individual variation in the effects of a tongue training task on MEP amplitudes. (C) 2009 Elsevier Ltd. All rights reserved.