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The exact nature of the role of Broca’s area in control of speech and whether it is exerted at the cognitive or at the motor level is still debated. Intraoperative evidence of a lack of motor responses to direct electrical stimulation (DES) of Broca’s area and the observation that its stimulation induces a “speech arrest” without an apparent effect on the ongoing activity of phono-articulatory muscles, raises the argument. Essentially, attribution of direct involvement of Broca’s area in motor control of speech, requires evidence of a functional connection of this area with the phono-articulatory muscles’ motoneurons. With a quantitative approach we investigated, in 20 patients undergoing surgery for brain tumors, whether DES delivered on Broca’s area affects the recruitment of the phono-articulatory muscles’ motor units. The electromyography (EMG) of the muscles active during two speech tasks (object picture naming and counting) was recorded during and in absence of DES on Broca’s area. Offline, the EMG of each muscle was analyzed in frequency (power spectrum, PS) and time domain (root mean square, RMS) and the two conditions compared. Results show that DES on Broca’s area induces an intensity-dependent “speech arrest.” The intensity of DES needed to induce “speech arrest” when applied on Broca’s area was higher when compared to the intensity effective on the neighboring pre-motor/motor cortices. Notably, PS and RMS measured on the EMG recorded during “speech arrest” were superimposable to those recorded at baseline. Partial interruptions of speech were not observed. Speech arrest was an “all-or-none” effect: muscle activation started only by removing DES, as if DES prevented speech onset. The same effect was observed when stimulating directly the subcortical fibers running below Broca’s area. Intraoperative data point to Broca’s area as a functional gate authorizing the phonetic translation to be executed by the motor areas. Given the absence of a direct effect on motor units recruitment, a direct control of Broca’s area on the phono-articulatory apparatus seems unlikely. Moreover, the strict correlation between DES-intensity and speech prevention, might attribute this effect to the inactivation of the subcortical fibers rather than to Broca’s cortical neurons.

目前学界仍存在争议的问题包括：布洛卡区（Broca’s area）在言语调控中的确切作用本质，以及其调控作用是发生在认知层面还是运动层面。针对布洛卡区的直接电刺激（direct electrical stimulation, DES）未引发运动反应，且该刺激可诱导"言语停顿"但对正在活动的语音发音肌肉（phono-articulatory muscles）无明显影响，上述术中观察结果引发了相关学术争论。本质而言，若要将布洛卡区归为言语运动控制的直接参与脑区，需要证明该脑区与语音发音肌肉（phono-articulatory muscles）的运动神经元（motoneurons）存在功能连接。本研究采用定量研究方法，对20名因脑肿瘤接受手术治疗的患者展开研究，旨在探究施加于布洛卡区的直接电刺激是否会影响语音发音肌肉（phono-articulatory muscles）的运动单位募集。研究记录了两种言语任务（物体图片命名与计数）中活跃肌肉的肌电图（electromyography, EMG），分别在布洛卡区施加直接电刺激与未施加刺激的条件下进行采集。离线分析阶段，我们从频域（power spectrum, PS）与时域（root mean square, RMS）两个维度对每块肌肉的肌电图信号进行分析，并对比两种实验条件下的检测结果。结果显示，施加于布洛卡区的直接电刺激可诱导强度依赖性的"言语停顿"现象。相较于邻近的运动前区/初级运动皮层的有效刺激强度，诱导"言语停顿"所需的布洛卡区直接电刺激强度更高。值得注意的是，"言语停顿"阶段采集的肌电图信号的功率谱与均方根值，与基线状态下的检测结果完全一致。研究未观察到不完全的言语中断情况，"言语停顿"呈现典型的全或无效应：仅在移除直接电刺激后，肌肉激活才会重新启动，仿佛直接电刺激阻断了言语的启动过程。当直接刺激布洛卡区下方走行的皮层下神经纤维时，也可观察到相同的效应。术中数据表明，布洛卡区可作为一道功能性闸门，授权运动脑区执行语音转译工作。鉴于其对运动单位募集无直接影响，布洛卡区直接控制语音发音装置的可能性似乎不大。此外，直接电刺激强度与言语阻断效应之间存在严格的相关性，这或许意味着该效应源于皮层下神经纤维的失活，而非布洛卡区皮层神经元的活动被抑制。