Reference frame coding in primate frontal cortex

背景：我们的日常行为包括将视觉信息转化为执行我们动作的肌肉的运动指令。这种视觉到运动的转换需要将进入以眼睛为中心的参考帧中的视网膜的视觉信号映射到相对于身体部分(例如头部、身体)在其他帧中执行的运动动作。这种参照系转换背后的神经机制还没有被很好地理解。我们以前曾假设，额叶的一个皮质区，即视觉和运动信息共存的补充眼场(SEF)，执行这种转换，然而这一假设尚未得到检验。目的：本文提出的实验将验证这一假说。该提案有两个主要目的。首先，研究在注视转移过程中，SEF内的不同神经元是否在不同的参照系中编码视觉和运动信息，以及这些神经元内参照系编码的时间动力学。第二，确定SEF神经元是否对不同的运动系统(即凝视和手臂运动)执行参照系转换。科学方法：我们将测量警觉(头部自由的)猴子的3D眼睛和头部运动，这些猴子被训练来执行两种不同的任务：a)让凝视从凝视点转向视觉目标，以及b)通过触摸屏幕来发出目标位置的信号，同时保持凝视在凝视点。通过分离眼睛、头部和身体的初始指向方向，并使用植入SEF皮质表面的电极微阵列记录神经元反应，我们将在两个任务中确定该区域内神经元激活的参考框架和时间动态。这应该揭示在海面基金中是否发生了参考框架转换。意义：该项目的结果可能与神经运动假体等快速发展的领域相关，因为它们将提供对灵长类额叶皮质中运动动作如何编码的洞察。我们的结果也可以用来建立视觉运动转换的计算模型，这将有助于理解运动控制的神经基础。

BACKGROUND: Our daily behavior involves the transformation of visual information into motor commands for the muscles that execute our actions. This visual-to-motor transformation requires mapping visual signals entering the retinas in an eye-centered reference frame into motor actions executed in other frames relative to body parts (e.g., head, body). The neural mechanisms underlying such reference frame transformation are not well understood. We have previously hypothesized that a cortical area of the frontal lobe, the Supplementary Eye Fields (SEF), in which visual and motor information coexist, performs the transformation, however this hypothesis has not been tested. OBJECTIVES: The experiments proposed here will test this hypothesis. The proposal has two main aims. First, to investigate whether during gaze shifts different neurons within the SEF encode visual and motor information in different reference frames as well as the temporal dynamics of reference frame coding within these neurons. Second, to determine whether SEF neurons perform reference frame transformations for different motor systems (i.e., gaze and arm movements). SCIENTIFIC APPROACH: We will measure eye and head movements in 3D of alert (head unrestrained) monkeys trained to perform two different tasks: a) to make gaze shifts toward a visual target from a fixation spot, and b) to signal the position of a target by touching a screen while keeping gaze on a fixation spot. By dissociating the initial eye, head and body pointing directions and recording neuronal responses using electrode microarrays implanted on the SEF cortical surface, we will determine the reference frame and temporal dynamic of neuronal activation within the area in both tasks. This should reveal whether reference frame transformations occur in the SEF. SIGNIFICANCE: The results of this project could be relevant to rapidly advancing fields such as neural motor prosthesis, since they will provide insight into how motor actions are encoded in the primate frontal cortex. Our results could also be used to build computational models of visuomotor transformations that will contribute to understanding the neural basis of motor control.