0069 The Different Effect of Tongue Motor Task Training (TTT) and Strength Training (ST) on the Modulation of Genioglossus Corticomotor Excitability in Rats

Abstract

The neuromuscular activation of upper airway stabilizing muscles, their propensity to fatigue and mechanical efficiency are pivotal in maintaining UA stability. Since training rats in a skilled reaching condition will induce task-related changes in the associated motor cortex, we aimed to investigate if different tongue training paradigms using fixed-training-intensity could differently induce neuroplastic changes in the corticomotor pathways, and to detect the time course of such changes. 18 water-restricted adult male Sprague-Dawley rats were trained to lick an isometric force-sensing disc at targeting forces for water reinforcement with sound feedback. In TTT group, 30–50% of maximal protrusion force (MPF) was used as a target window, while the ST paradigm used a progressive resistance training program with targeting force set above 50%, 60% and 70% of MPF, progressively. The rats in two groups were trained daily for two month with the same training intensity (1000 g·s per day). Corticomotor excitability was assessed via motor evoked potentials (MEPs) in genioglossus evoked by transcranial magnetic stimulation (TMS) at four sessions: at baseline before training, at different times after the 4th and 8th weeks of training. Overall, after 4 weeks in both groups, MEPs latencies of genioglossus evoked by TMS decreased immediately after training and dropped to the nadir 20 minutes after training compared to baseline (3.5 ± 0.5 ms vs. 4.8 ± 0.2 ms). This decreased latency lasted up to 80 minutes in TTT-treated rats; but in ST group, it rebound above the baseline value after 20 minutes and reached apex at 80 minutes (5.3 ± 0.4 ms). After 8 weeks in both groups, MEPs latencies consistently decreased within the 2 hours after training, and the precision of task performance (percent of peak force inside target window) significantly increased in TTT-treated rats. Tongue-task-training is associated with stable increment of genioglossus corticomotor excitability in a shorter time of training, while the tongue-strength-training rats might suffer fatigue at early stages of training. supported by the 2016 China National Nature Fund, number 81670085.