Mooney Ronan A, Bastian Amy J, Celnik Pablo A
Department of Physical Medicine and Rehabilitation, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
Kennedy Krieger Institute, Baltimore, MD, USA; Department of Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
Brain Stimul. 2023 Sep-Oct;16(5):1232-1239. doi: 10.1016/j.brs.2023.08.010. Epub 2023 Aug 17.
Subcortical motor pathways, such as the reticulospinal tract, are critical for producing and modulating voluntary movements and have been implicated in neurological conditions. Previous research has described the presence of ipsilateral motor evoked potentials (iMEPs) in the arm to transcranial magentic stimulation (TMS), and suggested they could be mediated by the uncrossed corticospinal tract or by ipsilateral cortico-reticulospinal connections. Here, we sought to elucidate the role of the reticulospinal tract in mediating iMEPs by assessing their modulation by a startling acoustic stimulus and mapping these responses across multiple upper limb effectors. In a first experiment, we delivered TMS at various intervals (1, 5, 10 and 15 ms) after a startling acoustic stimulus, known to excite the reticular formation, to elicit iMEPs in the arm. We observed robust facilitation of iMEP area when startle conditioning preceded TMS at the 10 ms interval. In a second experiment, we replicated our findings showing that both the area and number of iMEPs in the arm increases with startle conditioning. Using this technique, we observed that iMEPs are more prominent in the arm compared with the hand. In a third experiment, we also observed greater presence of iMEPs in flexor compared with extensor muscles. Together, these findings are consistent with properties of the reticulospinal tract observed in animals, suggesting that iMEPs primarily reflect reticulospinal activity. Our findings imply that we can use this approach to track modulation of cortico-reticulospinal excitability following interventions or neurological conditions where the reticulospinal tract may be involved in motor recovery.
皮质下运动通路，如网状脊髓束，对于产生和调节自主运动至关重要，并且与神经系统疾病有关。先前的研究描述了经颅磁刺激（TMS）时手臂中存在同侧运动诱发电位（iMEP），并表明它们可能由未交叉的皮质脊髓束或同侧皮质网状脊髓连接介导。在这里，我们试图通过评估惊人的听觉刺激对iMEP的调制作用并在多个上肢效应器上绘制这些反应，来阐明网状脊髓束在介导iMEP中的作用。在第一个实验中，我们在已知会激发网状结构的惊人听觉刺激后，以不同的间隔（1、5、10和15毫秒）给予TMS，以诱发手臂中的iMEP。我们观察到，当在10毫秒间隔时惊吓条件先于TMS时，iMEP面积有强烈的促进作用。在第二个实验中，我们重复了我们的发现，表明惊吓条件下手臂中iMEP的面积和数量都会增加。使用这种技术，我们观察到与手部相比，iMEP在手臂中更明显。在第三个实验中，我们还观察到与伸肌相比，屈肌中iMEP的存在更多。总之，这些发现与在动物中观察到的网状脊髓束的特性一致，表明iMEP主要反映网状脊髓活动。我们的发现意味着我们可以使用这种方法来跟踪在网状脊髓束可能参与运动恢复的干预或神经系统疾病后皮质网状脊髓兴奋性的调制。
