The Existence of the StartReact Effect Implies Reticulospinal, Not Corticospinal, Inputs Dominate Drive to Motoneurons during Voluntary Movement.
The Existence of the StartReact Effect Implies Reticulospinal, Not Corticospinal, Inputs Dominate Drive to Motoneurons during Voluntary Movement.
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DOI：
10.1523/jneurosci.2473-21.2022
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发表时间：
2022-10-05
影响因子：
5.3
通讯作者：
Baker, Stuart N.
中科院分区：
文献类型：
--
作者：
Tapia, Jesus A.;Tohyama, Takamichi;Poll, Annie;Baker, Stuart N.
如果伴随着一个响亮的（令人吃惊的）声音，反应时间会加快--“启动反应”效应。动物研究揭示了惊吓反射的网状脊髓基质; StartReact可能同样涉及网状脊髓束，但目前尚不确定。在这里，我们训练了两只雌性猕猴在视觉提示下进行肘部弯曲/伸展运动。提示有时伴随着响亮的声音，在肌电图反应延迟中产生StartReact效应，就像在人类身上看到的那样。从初级运动皮质（M1）、网状结构（RF）和脊髓（SC; C5-C8节段）中逆行鉴定的皮质脊髓神经元进行细胞外记录。在响亮的声音后，M1的任务相关活动受到抑制（潜伏期，提示后70-200 ms），但在RF中最初增强（70-80 ms），然后抑制（140-210 ms）。SC活性无变化。在一个计算模型中，我们模拟了一个运动神经元池接收输入从不同比例的平均M1和RF活动的实验记录。运动神经元放电产生模拟肌电图，允许反应时间测量。只有当运动神经元的驱动≥60%来自RF（≤40%来自M1）时，大声才能缩短反应时间。缩短的程度随着来自RF的更多驱动而增加。如果RF提供的驱动力小于60%，那么大声会延长反应时间，这与实验结果相反。因此，自主运动的大部分驱动力可能来自脑干，而不是皮层; StartReact效应的大小变化可以衡量下行系统相对重要性的变化。我们的研究结果表明，一个响亮的声音有相反的影响，从初级运动皮层皮质脊髓细胞的神经尖峰，在网状结构。我们发现，这偶然允许由响亮的声音产生的反应时间的变化被用来评估相对重要性的网状脊髓与皮质脊髓运动控制，验证以前的非侵入性测量在人类。我们的研究结果表明，大部分的下行驱动运动神经元产生自愿运动的灵长类动物来自网状脊髓束，而不是皮质脊髓束。
Reaction time is accelerated if a loud (startling) sound accompanies the cue—the “StartReact” effect. Animal studies revealed a reticulospinal substrate for the startle reflex; StartReact may similarly involve the reticulospinal tract, but this is currently uncertain. Here we trained two female macaque monkeys to perform elbow flexion/extension movements following a visual cue. The cue was sometimes accompanied by a loud sound, generating a StartReact effect in electromyogram response latency, as seen in humans. Extracellular recordings were made from antidromically identified corticospinal neurons in primary motor cortex (M1), from the reticular formation (RF), and from the spinal cord (SC; C5–C8 segments). After loud sound, task-related activity was suppressed in M1 (latency, 70–200 ms after cue), but was initially enhanced (70–80 ms) and then suppressed (140–210 ms) in RF. SC activity was unchanged. In a computational model, we simulated a motoneuron pool receiving input from different proportions of the average M1 and RF activity recorded experimentally. Motoneuron firing generated simulated electromyogram, allowing reaction time measurements. Only if ≥60% of motoneuron drive came from RF (≤40% from M1) did loud sound shorten reaction time. The extent of shortening increased as more drive came from RF. If RF provided <60% of drive, loud sound lengthened the reaction time—the opposite of experimental findings. The majority of the drive for voluntary movements is thus likely to originate from the brainstem, not the cortex; changes in the magnitude of the StartReact effect can measure a shift in the relative importance of descending systems. SIGNIFICANCE STATEMENT Our results reveal that a loud sound has opposite effects on neural spiking in corticospinal cells from primary motor cortex, and in the reticular formation. We show that this fortuitously allows changes in reaction time produced by a loud sound to be used to assess the relative importance of reticulospinal versus corticospinal control of movement, validating previous noninvasive measurements in humans. Our findings suggest that the majority of the descending drive to motoneurons producing voluntary movement in primates comes from the reticulospinal tract, not the corticospinal tract.