Assessing the contribution of a subcortical circuit for express visuomotor responses

视觉是人类在外部环境中识别物体的主要感官。许多日常动作需要将视觉信息转化为适当的肌肉活动模式。这种视觉到运动的转变可以发生得非常快：快速扫视或颈部或肢体肌肉恢复的最早阶段可以在视觉目标出现后100毫秒内发生。我的研究项目旨在了解大脑是如何产生如此快速的反应的。我们假设，无论是在眼睛、头部还是肢体产生的表达反应，都是由起源于上丘（SC）的共同织网-脊髓通路发起的。为了验证这一点，我们建议在人类和非人类灵长类动物（NHPs）中进行互补的行为和神经生理学实验。在项目1中，我们将测量眼球运动、颈部和上肢肌肉的活动，当人类在过去的发现基金中开发的一项新目标任务中进行视觉引导时。在这个任务中，受试者试图抓住一个从障碍物后面出现的移动目标。在这项任务中，几乎每个受试者的上肢肌肉都产生了表达反应，这使我们能够评估每个受试者和每个试验中眼睛、头部和肢体的表达反应的相关性。我们还将测试通过网状脊髓系统产生短潜伏期反应的触电声刺激是否会影响表达反应的时间和/或幅度。最后，由于网状脊髓系统是双侧的，我们将检查上肢的表达反应是否在被试选择用哪只手臂捕捉新出现的目标的修改任务中双侧表达。项目1的工作只能间接测试潜在的神经机制。在项目2中，我们将研究NHPs执行新出现的目标任务时的表达反应的神经生理学，记录眼睛、颈部和肢体的反应，就像在人类中一样。然后，我们将记录SC的信号，以评估目标出现后的信号时间，并相对于眼睛、头部和肢体的表达反应。最后，我们将对SC的失活通常会改变眼睛、头部和肢体的表达反应的预测进行因果检验。长期以来，人们一直认识到，神经回路的层次结构有助于自发的视觉引导行为，脊髓和脑干回路与皮层回路协同作用，以确保情境适当的行为。通过利用我们开发的一种新颖的行为任务来可靠地唤起表达反应，我们现在可以测试一个在系统发育上保守的构造-网状-脊髓回路在表达反应中的作用。这项工作最终将有助于更好地理解皮层和皮层下回路如何在动态和不确定的世界中协同工作，在时间紧迫的情况下产生适合情境的动作。

Vision is the main sense humans use to identify objects in the external environment. Many everyday actions require a transformation of visual information into the appropriate patterns of muscle activity. Such visual-to-motor transformations can occur remarkably fast: express saccades or the earliest phase of neck or limb muscle recruitment can occur within 100 ms of visual target onset. My research program seeks to understand how the brain generates such rapid responses. We hypothesize that express responses, be they generated at the eye, head, or limb, are initiated by a common tecto-reticulo-spinal pathway originating in the superior colliculus (SC). To test this, we propose complementary behavioural and neurophysiological experiments in humans and non-human primates (NHPs). In Project 1, we will measure eye movements and the activity of neck and upper limb muscles while humans perform visually-guided reaches in a novel emerging target task developed during the past Discovery Grant. In this task, subjects try to catch a moving target that emerges from behind a barrier. Express responses are produced on upper limb muscles in virtually every subject in this task, allowing us to assess subject-by-subject and trial-by-trial correlations of express responses across the eyes, head, and limb. We will also test whether startling acoustic stimuli, which engender short-latency responses via the reticulospinal system, influence the timing and/or magnitude of express responses. Finally, since the reticulospinal system projects bilaterally, we will examine whether express responses in the upper limb are expressed bilaterally in a modified task where subjects choose which arm to use to catch the emerging target. The work in Project 1 can only indirectly test underlying neural mechanisms. In Project 2, we will examine the neurophysiology of express responses in NHPs performing the emerging target task, recording eye, neck, and limb responses as in humans. We will then record from the SC to assess signal timing after target emergence and relative to express responses at the eyes, head and limb. Finally, we will causally test the prediction that inactivation of SC should commonly modify express responses of the eyes, head, and limb. It has long been appreciated that a hierarchy of neural circuits contributes to voluntary visually-guided actions, with spinal cord and brainstem circuits acting in concert with cortical circuits to ensure contextually-appropriate actions. By leveraging a novel behavioural task that we developed to reliably evoke express responses, we can now test the contribution of a largely unappreciated role for a phylogenetically-conserved tecto-reticulo-spinal circuit in express responses. This work will ultimately contribute to a better understanding of how cortical and subcortical circuits work together in a dynamic and uncertain world to generate contextually-appropriate actions when time is of the essence.