Sowman Paul F, Flavel Stanley C, McShane Christie L, Sakuma Shigemitsu, Miles Timothy S, Nordstrom Michael A
Research Centre for Human Movement Control, Discipline of Physiology, School of Molecular and Biomedical Sciences, The University of Adelaide, Adelaide 5005, South Australia, Australia.
J Neurophysiol. 2009 Jul;102(1):159-66. doi: 10.1152/jn.90894.2008. Epub 2009 May 6.
Like most of the cranial muscles involved in speech, the trigeminally innervated anterior digastric muscles are controlled by descending corticobulbar projections from the primary motor cortex (M1) of each hemisphere. We hypothesized that changes in corticobulbar M1 excitability during speech production would show a hemispheric asymmetry favoring the left side, which is the dominant hemisphere for language processing in most strongly right handed subjects. Fifteen volunteers aged 24.5+/-5.3 (SD) yr participated. All subjects were strongly right handed as reported by questionnaire. A surface electromyograph (EMG) was recorded bilaterally from digastrics and jaw movement detected by an accelerometer attached to a lower incisor. Focal transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability of the digastric representation in M1 of both hemispheres during four tasks: 1) static isometric contraction of digastrics; 2) speaking a single word; 3) visually guided, nonspeech jaw movement that matched the jaw kinematics recorded during task 2; and 4) reciting a sentence. Background EMG was well matched in all tasks and jaw kinematics were similar around the time of the TMS pulse for tasks 2-4. TMS resting thresholds and digastric muscle-evoked potential (MEP) size during isometric contraction did not differ for TMS over left versus right M1. MEPs elicited by TMS over left, but not right M1 increased in size during speech and nonspeech jaw movement compared with isometric contraction. We conclude that left corticobulbar M1 is preferentially engaged for descending control of digastric muscles during speech and the performance of a rapid jaw movement to match a target kinematic profile.
与大多数参与言语活动的颅部肌肉一样，由三叉神经支配的前腹直肌受每个半球初级运动皮层（M1）下行的皮质延髓投射控制。我们假设，在言语产生过程中，皮质延髓M1兴奋性的变化会表现出半球不对称性，有利于左侧，在大多数右利手受试者中，左侧是语言处理的优势半球。15名年龄在24.5±5.3（标准差）岁的志愿者参与了研究。所有受试者通过问卷报告均为强右利手。使用表面肌电图（EMG）双侧记录腹直肌的活动，并通过附着在下切牙上的加速度计检测下颌运动。在四项任务期间，使用局灶性经颅磁刺激（TMS）评估双侧半球M1中腹直肌代表区的皮质运动兴奋性：1）腹直肌的静态等长收缩；2）说出单个单词；3）视觉引导的、与任务2中记录的下颌运动学相匹配的非言语下颌运动；4）背诵句子。在所有任务中，背景肌电图匹配良好，在任务2 - 4的TMS脉冲时刻左右，下颌运动学相似。在等长收缩期间，左侧与右侧M1的TMS静息阈值和腹直肌诱发电位（MEP）大小没有差异。与等长收缩相比，在言语和非言语下颌运动期间，左侧M1而非右侧M1经TMS诱发的MEP大小增加。我们得出结论，在言语和快速下颌运动以匹配目标运动学特征的过程中，左侧皮质延髓M1优先参与对腹直肌的下行控制。
