Indexing covert activity within the oculomotor system via recordings of neck muscle activity

人类通过快速改变视线的运动来探索他们的视觉环境。没有头部运动的眼球跳动是人类最容易理解的意志力运动。然而，由于眼睛嵌套在移动的头部中，眼球运动系统进化成控制凝视，眼睛和头部的协调运动带来了巨大的凝视转移(凝视=眼睛在空间=头部在眼睛+头部在空间)。无处不在、快速和准确的眼睛-头部凝视转移使其成为了解大脑如何协调多节段运动的模型系统。 我们假设，眼球运动系统通过控制相对于较高的“凝视”阈值和较低的“头部”阈值的神经活动，允许选择性地招募头部运动，而不是凝视转移。在这里，我们通过检查颈部肌肉记录索引隐蔽眼球运动计划的好坏，在人类身上检验这一假设。颈部肌肉记录避开了头部运动固有的生物力学复杂性，并在逐个试验的基础上提供了一种直接的神经控制措施。其中一个目标将是记录任务期间的颈部肌肉活动，因为在此类任务中制定的隐蔽眼球运动计划是很好理解的，这将在不同的反应方案之间建立竞争。这种方法提供了一种机会，可以将颈部肌肉活动与从计算模型得出的隐蔽眼动过程的估计进行比较。第二种方法是在短暂的经颅磁刺激(TMS)脉冲后检查颈部肌肉的活动。我们最近已经证明，颈部肌肉反应是由额叶眼场(FEF)的TMS引起的，现在我们希望通过使用这种诱发反应来利用这一发现，如在大规模凝视转移的隐蔽计划中分析FEF参与。整个提案项目的共同主题是，人类的颈部肌肉活动为发展动眼项目提供了一个客观的衡量标准，否则，由于凝视轴的稳定，这些项目将被认为是“隐蔽的”。

Humans explore their visual environment through orienting movements that rapidly change their line of sight. Small saccadic eye movements made without head movements are arguably the best understood volitional movement made by humans. However, because the eyes are nested within a mobile head, the oculomotor system evolved to control gaze, and large gaze shifts are brought about by coordinated movements of the eyes and head (gaze = eye-in-space = eye-in-head + head-in-space). The ubiquity, rapidity, and accuracy of eye-head gaze shifts make it a model system for understanding how the brain coordinates multi-segmental motion. We have hypothesized that the oculomotor system permits selective recruitment of head movements without gaze shifts by controlling neural activity relative to a high "gaze" threshold and a lower "head" threshold. Here, we test this hypothesis in humans by examining how well neck muscle recordings index covert oculomotor plans. Neck muscle recordings circumvent the biomechanical complexities inherent to head motion, and provide a direct measure of neural control on a trial-by-trial basis. One aim will be to record neck muscle activity during tasks that set up a competition between response alternatives, as the covert oculomotor plans developing during such tasks are well understood. Such an approach provides an opportunity to compare neck muscle activity with estimates of covert oculomotor processes derived from computational models. A second approach will be to examine neck muscle activity following brief pulses of transcranial magnetic stimulation (TMS). We have recently demonstrated that a neck muscle response is evoked by TMS of the frontal eye fields (FEF), and we now look to leverage this finding by using such evoked responses as an assay of FEF engagement during covert plans for large gaze shifts. The common theme throughout this proposal projects is that neck muscle activity in humans provides an objective measure into developing oculomotor projects that would otherwise be deemed "covert" by virtue of stability of the gaze axis.