The effects of training time, sensory loss and pain on human motor learning

This study determined, in humans, the effects of (i) the number of within-session task repetitions (72 or 144 over a period of 15 or 30 min, respectively) on the time course of motor learning in a long-term (seven consecutive daily motor-training sessions and a 1-week post-follow-up) novel tongue-task training regime and (ii) somatosensory manipulations (capsaicin-induced intra-oral pain or lidocaine-induced sensory loss of the tongue tip) on motor learning in a short-term (single motor-training session consisting of 72 within-session task repetitions over a period of 15 min) novel tongue-task training regime. Novel tongue-task training consisted of tracking a moving target box by generating a pre-set amount of tongue-protrusion force onto a force lever. Analysis of motor behaviour revealed (i) a higher within-session gain for the 30-min tongue-task training regime, but this difference did not differentially affect the time course of the overall motor performance or additional motor performance variables between the 15- and 30-min tongue-task training regimes in subsequent training sessions. (ii) somatosensory manipulations of the tongue tip reduced the gains in overall motor performance, and this reduced motor performance was mainly characterized by exaggerated undershoot errors and delayed reaction times for the lidocaine tongue-task training regime and exaggerated overshoot and undershoot errors as well as delayed reaction times for the capsaicin tongue-task training regime. It is concluded that extended within-session task repetitions do not facilitate additional long-term gains in overall motor performance and intra-oral sensory loss or pain hinders motor learning.