Haskins Laboratories, New Haven, Connecticut.
Department of Psychology, McGill University, Montreal, Quebec, Canada.
J Neurophysiol. 2019 Oct 1;122(4):1397-1405. doi: 10.1152/jn.00383.2019. Epub 2019 Aug 7.
Motor learning is associated with plasticity in both motor and somatosensory cortex. It is known from animal studies that tetanic stimulation to each of these areas individually induces long-term potentiation in its counterpart. In this context it is possible that changes in motor cortex contribute to somatosensory change and that changes in somatosensory cortex are involved in changes in motor areas of the brain. It is also possible that learning-related plasticity occurs in these areas independently. To better understand the relative contribution to human motor learning of motor cortical and somatosensory plasticity, we assessed the time course of changes in primary somatosensory and motor cortex excitability during motor skill learning. Learning was assessed using a force production task in which a target force profile varied from one trial to the next. The excitability of primary somatosensory cortex was measured using somatosensory evoked potentials in response to median nerve stimulation. The excitability of primary motor cortex was measured using motor evoked potentials elicited by single-pulse transcranial magnetic stimulation. These two measures were interleaved with blocks of motor learning trials. We found that the earliest changes in cortical excitability during learning occurred in somatosensory cortical responses, and these changes preceded changes in motor cortical excitability. Changes in somatosensory evoked potentials were correlated with behavioral measures of learning. Changes in motor evoked potentials were not. These findings indicate that plasticity in somatosensory cortex occurs as a part of the earliest stages of motor learning, before changes in motor cortex are observed. We tracked somatosensory and motor cortical excitability during motor skill acquisition. Changes in both motor cortical and somatosensory excitability were observed during learning; however, the earliest changes were in somatosensory cortex, not motor cortex. Moreover, the earliest changes in somatosensory cortical excitability predict the extent of subsequent learning; those in motor cortex do not. This is consistent with the idea that plasticity in somatosensory cortex coincides with the earliest stages of human motor learning.
运动学习与运动和体感皮层的可塑性有关。动物研究表明，单独对这些区域进行强直刺激会在其对应区域诱导长时程增强。在这种情况下，运动皮层的变化可能有助于体感变化，而体感皮层的变化可能与大脑运动区域的变化有关。也有可能是学习相关的可塑性独立发生在这些区域。为了更好地理解运动皮层和体感皮层可塑性对人类运动学习的相对贡献，我们评估了运动技能学习过程中初级体感和运动皮层兴奋性变化的时间进程。学习是通过使用力产生任务来评估的，其中目标力曲线在每次试验中都有所变化。初级体感皮层的兴奋性是通过正中神经刺激引起的体感诱发电位来测量的。初级运动皮层的兴奋性是通过单脉冲经颅磁刺激诱发的运动诱发电位来测量的。这两个测量值与运动学习试验块交替进行。我们发现，学习过程中皮层兴奋性的最早变化发生在体感皮层反应中，这些变化先于运动皮层兴奋性的变化。体感诱发电位的变化与学习的行为测量相关。运动诱发电位的变化则不相关。这些发现表明，体感皮层的可塑性发生在运动学习的最早阶段，在观察到运动皮层的变化之前。我们在运动技能习得过程中跟踪体感和运动皮层的兴奋性。在学习过程中观察到运动皮层和体感皮层兴奋性的变化；然而，最早的变化发生在体感皮层，而不是运动皮层。此外，体感皮层兴奋性的最早变化预测了随后学习的程度；运动皮层的变化则不相关。这与体感皮层的可塑性与人类运动学习的最早阶段同时发生的观点一致。
