Increased occlusal vertical dimension induces modulation of masticatory feedforward control

以往的研究表明，初级运动皮层（M1）的功能可塑性与运动技能学习和环境变化有关。增加咬合垂直尺寸（iOVD）可以调节咀嚼，如在咀嚼周期，周期，和下颌肌梭的放电特性。然而，关于iOVD后面部初级运动皮层（face-M1）内运动表征的变化知之甚少。本研究的目的是使用皮质内微刺激（ICMS）确定iOVD对面部M1的影响。在iOVD组中，上颌磨牙用丙烯酸树脂构建2 mm。在iOVD后1、2和8周，记录ICMS在右侧面M1内诱发的左（LAD）和右（RAD）前二腹肌（AD）、咬肌和颏舌肌（GG）的肌电图（EMG）活动。IOVD与ICMS诱发LAD和/或GG EMG活动的面M1内的部位数量显著增加相关，并且在1周和2周时RAD和LAD肌肉的重心发生侧向移位，但在8周时不相关。这些发现表明，大鼠面M1内的时间依赖性神经可塑性变化与iOVD相关。这可能与动物适应口腔环境变化的能力有关。

Previous studies have demonstrated that functional plasticity in the primary motor cortex (M1) is related to motor-skill learning and changes in the environment. Increased occlusal vertical dimension (iOVD) may modulate mastication, such as in the masticatory cycle, cycle, and the firing properties of jaw-muscle spindles. However, little is known about the changes in motor representation within the face primary motor cortex(face-M1) after iOVD. The purpose of the present study was to determine the effect of iOVD on the face-M1 using intracortical microstimulation (ICMS). In an iOVD group, the maxillary molars were built-up by 2 mm with acrylic. The electromyographic (EMG) activities from the left (LAD) and right (RAD) anterior digastric (AD), masseter and genioglossus (GG) muscles elicited by ICMS within the right face-M1 were recorded 1, 2 and 8 weeks after iOVD. IOVD was associated with a significant increase in the number of sites within the face-M1 from which ICMS evoked LAD and/or GG EMG activities, as well as a lateral shift in the center of gravity of the RAD and LAD muscles at 1 and 2 weeks, but not at 8 weeks. These findingssuggest that a time-dependent neuroplastic change within the rat face-M1 occurs in association with iOVD. This may be related to the animal’s ability to adapt to a change in the oral environment.