Increased occlusal vertical dimension induces modulation of masticatory feedforward control

先前的研究表明，初级运动皮质(M1)的功能可塑性与运动技能学习和环境变化有关。咬合垂直尺寸(IOVD)的增加可能会调节咀嚼，例如在咀嚼周期、周期和颌肌梭的激发特性中。然而，对iOVD后面部初级运动皮质(Face-M1)内运动表征的变化知之甚少。本研究的目的是通过皮层内微刺激(ICMS)来确定iOVD对Face-M1的影响。在iOVD组，上颌磨牙用亚克力材料堆积2 mm。分别于iOVD后1、2、8周记录ICMS在右侧面肌M1内诱发的左(LAD)、右(RAD)前二腹肌(AD)、咬肌(GG)和颧舌肌(GG)的肌电活动。IOVD与ICMS诱发LAD和/或GG肌电活动的Face-M1内部位的数量显著增加有关，并且在1周和2周时RAD和LAD肌肉的重心横向移动，但在8周时不相关。这些发现表明，大鼠Face-M1内的神经可塑性变化与iOVD有关。这可能与动物对口腔环境变化的适应能力有关。

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.