The Cortical Representation of Oculomotor Proprioception

描述(申请人提供)：我们必须知道一个物体在视觉空间中相对于身体的位置，以便看着它，朝向它或远离它，伸手触摸它，抓住它，甚至向它扔东西。视觉信息通过视网膜进入大脑，但由于视网膜在轨道上移动，知道某物在视网膜上的位置并不能自动告诉大脑它在太空中的位置。为了计算物体在太空中的位置，大脑不仅必须知道它在视网膜中的位置，还必须知道视网膜在空间中的位置。大脑通过内耳前庭系统的信号和颈部肌肉中的传感器知道头部在太空中的位置。大脑的视觉关联皮质中有信号报告眼睛在轨道中的位置，但这种眼睛位置信息的来源尚不清楚。一种可能性是，眼睛位置信号的来源是运动系统的必然放电，因为控制眼睛运动的肌肉的信号有一个分量，表示眼睛的位置。我们之前已经发现了这样一个必然的信号，它向大脑皮层神经元报告即将到来的眼球运动的尺寸。另一种可能性是，眼外肌中的传感器向大脑发送信号，描述眼睛在轨道中的位置。猴子和人类眼外肌有许多传感器，看起来就像骨骼肌中的传感器，发出肌肉长度的信号。这些感受器通过丘脑投射到初级躯体感觉皮质(SI)的3a区和第二躯体感觉皮质(SLL)。在非常初步的实验中，我们在3a区和SLL区(通过磁共振成像识别)都发现了描述眼睛在轨道中位置的细胞。这项建议有两个目标：1)表征眼睛位置信号，观察其眼动、视觉和注意特性。2)通过麻醉一只眼睛的眼眶来确定该信号是本体感觉起源还是必然起源。这些实验将提供对大脑分析空间感知和行动的机制的洞察，并将帮助我们理解和设计空间行为缺陷的康复策略，例如涉及顶叶皮质的中风后发生的，SI和SLL是其中的一部分。

DESCRIPTION (provided by applicant): We have to know where an object is in visual space relative to the body, in order to look at it, move towards it or away from it, reach out and touch it, grasp it, or even throw something at it. Visual information enters the brain via the retina, but because the retina moves in the orbit, knowing where something is on the retina does not automatically tell the brain where it is in space. In order to calculate where something is in space, the brain must know not only where it is in the retina, but where the retina is in space. The brain knows where the head is in space from signals from the vestibular system in the inner ear, and from sensors in the neck muscles. There are signals in the visual association cortex of the brain that report where the eye is in the orbit, but the source of this eye position information is unknown. One possibility is that the source of the eye position signal arises as a corollary discharge from the motor system, because the signal controlling the muscles that move the eye has a component signaling the position of the eye. We have previously discovered such a corollary signal which reports the dimensions of an impending eye movement to cortical neurons. The other possibility is that sensors in the extraocular muscles send a signal to the brain describing the position of the eye in the orbit. Monkey and human extraocular muscles have many sensors which look like the sensors in the skeletal muscles that signal muscle length. These sensors project through the thalamus to area 3a in primary somatosensory cortex (SI), and to the second somatosensory cortex (Sll). In very preliminary experiments we have found cells in both area 3a and Sll (as identified by magnetic resonance imaging) which describe the position of the eye in the orbit. This proposal has two aims: 1) to characterize the eye position signal, looking at its oculomotor, visual, and attentional properties. 2) to determine by anesthetizing the orbit of one eye, if the signal has a proprioceptive or a corollary origin. These experiments will provide insight into the mechanisms by which the brain analyzes space for perception and action, and will help us understand and design rehabilitative strategies for deficits in spatial behavior such as occur after strokes involving the parietal cortex, of which SI and Sll form a component.