Brain-derived neurotrophic factor (BDNF) plays an important role in learning, memory, and brain plasticity. Humans with a val66met polymorphism in the BDNF gene have reduced levels of BDNF and alterations in motor learning and short-term cortical plasticity. In the current study, we sought to further explore the role of BDNF in motor learning by testing human subjects on a visuomotor adaptation task. In experiment 1, 21 subjects with the polymorphism (val/met) and 21 matched controls (val/val) were tested during learning, short-term retention (45 min), long-term retention (24 h), and de-adaptation of a 60° visuomotor deviation. We measured both mean error as well as rate of adaptation during each session. There was no difference in mean error between groups; however, val/met subjects had a reduced rate of adaptation during learning as well as during long-term retention, but not short-term retention or de-adaptation. In experiment 2, 12 val/met and 12 val/val subjects were tested on a larger 80° deviation, revealing a more pronounced difference in mean error during adaptation than the 60° deviation. These results suggest that BDNF may play an important role in visuomotor adaptive processes in the human.

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After repeated jumps over an elastic surface (e.g. a trampoline), subjects usually report a strange sensation when they jump again overground (e.g. they feel unable to jump because their body feels heavy). However, the motor and sensory effects of exposure to an elastic surface are unknown. In the present study, we examined the motor and perceptual effects of repeated jumps over two different surfaces (stiff and elastic), measuring how this affected maximal countermovement vertical jump (CMJ). Fourteen subjects participated in two counterbalanced sessions, 1 week apart. Each experimental session consisted of a series of maximal CMJs over a force plate before and after 1 min of light jumping on an elastic or stiff surface. We measured actual motor performance (height jump and leg stiffness during CMJ) and how that related to perceptual experience (jump height estimation and subjective sensation). After repeated jumps on an elastic surface, the first CMJ showed a significant increase in leg stiffness (P < or = 0.01), decrease in jump height (P < or = 0.01) increase in perceptual misestimation (P < or = 0.05) and abnormal subjective sensation (P < or = 0.001). These changes were not observed after repeated jumps on a rigid surface. In a complementary experiment, continuous surface transitions show that the effects persist across cycles, and the effects over the leg stiffness and subjective experience are minimized (P < or = 0.05). We propose that these aftereffects could be the consequence of an erroneous internal model resulting from the high vertical forces produced by the elastic surface.

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