Department of Physical Medicine and Rehabilitation, Johns Hopkins University, Baltimore, MD, USA.
Kennedy Krieger Institute, Baltimore, MD, USA; Department of Neuroscience, Johns Hopkins University, Baltimore, MD, USA.
Cortex. 2021 Oct;143:47-56. doi: 10.1016/j.cortex.2021.06.014. Epub 2021 Jul 17.
Learning similar motor skills in close succession is limited by interference, a phenomenon that takes place early after acquisition when motor memories are unstable. Interference can be bidirectional, as the first memory can be disrupted by the second (retrograde interference), or the second memory can be disrupted by the first (anterograde interference). The heightened plastic state of primary motor cortex after learning is thought to underlie interference, as unstable motor memories compete for neural resources. While time-dependent consolidation processes reduce interference, the passage of time (~6 h) required for memory stabilization limits our capacity to learn multiple motor skills at once. Here, we demonstrate in humans that prolonged training at asymptote of an initial motor skill reduces both retrograde and anterograde interference when a second motor skill is acquired in close succession. Neurophysiological assessments via transcranial magnetic stimulation reflect this online stabilization process. Specifically, excitatory neurotransmission in primary motor cortex increased after short training and decreased after prolonged training at performance asymptote. Of note, this reduction in intracortical excitation after prolonged training was proportional to better skill retention the following day. Importantly, these neurophysiological effects were not observed after motor practice without learning or after a temporal delay. Together, these findings indicate that prolonged training at asymptote improves the capacity to learn multiple motor skills in close succession, and that downregulation of excitatory neurotransmission in primary motor cortex may be a marker of online motor memory stabilization.
在紧密相继的情况下学习相似的运动技能受到干扰的限制，这种现象发生在获得运动记忆不稳定之后的早期。干扰可以是双向的，第一个记忆可以被第二个记忆干扰（逆行干扰），或者第二个记忆可以被第一个记忆干扰（顺行干扰）。学习后初级运动皮层的高度可塑性状态被认为是干扰的基础，因为不稳定的运动记忆争夺神经资源。虽然依赖时间的巩固过程会减少干扰，但记忆稳定所需的时间（约 6 小时）限制了我们一次学习多个运动技能的能力。在这里，我们在人类中证明，在初始运动技能达到渐近线时进行长时间训练会减少紧随其后获得的第二个运动技能的逆行和顺行干扰。通过经颅磁刺激进行的神经生理学评估反映了这种在线稳定过程。具体来说，在短时间训练后初级运动皮层中的兴奋性神经传递增加，而在长时间训练达到表现渐近线后则减少。值得注意的是，这种长时间训练后皮层内兴奋的减少与第二天更好的技能保留成正比。重要的是，这些神经生理学效应在没有学习的运动练习或在时间延迟后观察不到。总之，这些发现表明在渐近线进行长时间训练可以提高紧密相继学习多个运动技能的能力，而初级运动皮层中兴奋性神经传递的下调可能是在线运动记忆稳定的标志物。
