Department of Neuroscience.
Zuckerman Institute, Columbia University, New York 10027, New York.
J Neurosci. 2019 Apr 24;39(17):3217-3233. doi: 10.1523/JNEUROSCI.2335-18.2019. Epub 2019 Feb 12.
The contribution of the supplementary motor area (SMA) to movement initiation remains unclear. SMA exhibits premovement activity across a variety of contexts, including externally cued and self-initiated movements. Yet SMA lesions impair initiation primarily for self-initiated movements. Does SMA influence initiation across contexts or does it play a more specialized role, perhaps contributing only when initiation is less dependent on external cues? To address this question, we perturbed SMA activity via microstimulation at variable times before movement onset. Experiments used two adult male rhesus monkeys trained on a reaching task. We used three contexts that differed regarding how tightly movement initiation was linked to external cues. Movement kinematics were not altered by microstimulation. Instead, microstimulation induced a variety of changes in the timing of movement initiation, with different effects dominating for different contexts. Despite their diversity, these changes could be explained by a simple model where microstimulation has a stereotyped impact on the probability of initiation. Surprisingly, a unified model accounted for effects across all three contexts, regardless of whether initiation was determined more by external cues versus internal considerations. All effects were present for stimulation both contralateral and ipsilateral to the moving arm. Thus, the probability of initiating a pending movement is altered by perturbation of SMA activity. However, changes in initiation probability are independent of the balance of internal and external factors that establish the baseline initiation probability. The role of the supplementary motor area (SMA) in initiating movement remains unclear. Lesion experiments suggest that SMA makes a critical contribution only for self-initiated movements. Yet SMA is active before movements made under a range of contexts, suggesting a less-specialized role in movement initiation. Here, we use microstimulation to probe the role of SMA across a range of behavioral contexts that vary in the degree to which movement onset is influenced by external cues. We demonstrate that microstimulation produces a temporally stereotyped change in the probability of initiation that is independent of context. These results argue that SMA participates in the computations that lead to movement initiation and does so across a variety of contexts.
补充运动区（SMA）对运动起始的贡献尚不清楚。SMA 在各种情况下都会表现出运动前活动，包括外部提示和自我发起的运动。然而，SMA 损伤主要影响自我发起的运动的起始。SMA 是否影响跨情境的起始，或者它是否发挥更专门的作用，也许只在起始不太依赖外部提示时才发挥作用？为了解决这个问题，我们通过在运动开始前的不同时间对 SMA 进行微刺激来干扰 SMA 的活动。实验使用了两只成年雄性恒河猴，它们在一项抓握任务中接受训练。我们使用了三种不同的情境，这些情境在运动起始与外部提示的紧密程度上有所不同。微刺激不会改变运动的运动学。相反，微刺激会导致运动起始时间的各种变化，不同的情境会产生不同的效果。尽管它们的多样性，这些变化可以用一个简单的模型来解释，其中微刺激对起始的概率有一个刻板的影响。令人惊讶的是，一个统一的模型可以解释所有三种情境的效应，无论起始是更多地由外部提示还是内部因素决定。所有的影响在刺激对侧和同侧手臂时都存在。因此，通过干扰 SMA 活动，可以改变待发运动的起始概率。然而，起始概率的变化与确定起始基线概率的内部和外部因素的平衡无关。补充运动区（SMA）在运动起始中的作用尚不清楚。损伤实验表明，SMA 仅对自我发起的运动做出关键贡献。然而，SMA 在一系列情境下的运动前都很活跃，这表明它在运动起始中的作用不那么专门化。在这里，我们使用微刺激来探测 SMA 在一系列行为情境中的作用，这些情境在运动起始受外部提示影响的程度上有所不同。我们证明，微刺激会产生一个时间上刻板的起始概率变化，与情境无关。这些结果表明，SMA 参与了导致运动起始的计算，并在各种情境中都有参与。
