The morphological basis to the mammalian vestibulo-ocular system: the influence of skull architecture locomotion and phylogeny

目不转睛地盯着远处的物体，朝它走去。当你走路时，你的眼球会不停地移动，以补偿你头部的运动。负责监测头部运动并将信息提供给眼球肌肉的结构是内耳的半规管。有三个这种半月形的管道，一个对应头部的每一次旋转(例如，向上向下旋转，向左向右旋转和左右倾斜)。这些信息通过大脑提供给三对肌肉，这些肌肉可以将眼球朝与头部相反的方向移动(例如，向下倾斜、向左旋转和向右向左倾斜)。管道和肌肉对所有脊椎动物的生命都至关重要。如果导管和肌肉之间没有快速的沟通，眼睛的代偿性运动会滞后于运动中的头部运动，眼睛视网膜上的图像会变得模糊，你很快就会感到头晕，最终摔倒。这些都是患有梅尼埃病等疾病的患者所经历的严重虚弱的症状。显然，眼部肌肉必须快速移动，以抵消被眼管感知到的头部运动。因此，您可能会想象通过每对肌肉的平面与提供主要输入的半规管平面对齐(例如，上下导管平行于将眼睛上下移动的肌肉对)。这样，信号输出将与所需的动作方向紧密匹配(例如，通过上下移动鼠标而不是左右或对角线移动计算机光标是最容易的)。这种信号和动作的紧密空间匹配将最大限度地减少大脑对信号进行耗时的重新调整的需要。因为对齐排列似乎是最简单和最符合逻辑的，人们认为平面确实是平行的，或者接近平行。几十年来，这一假设逐渐得到人们的信任，甚至出现在一些教科书中，并作为内耳和眼睛肌肉功能的数学模型的基础。然而，事实证明，虽然非常有限，但有证据表明，这些平面并不平行，因此大脑必须对来自管道的信号进行一些处理。问题是，由于眼肌和眼管通常无法进行身体检查，现有的数据太少，无法确定平面之间的差异程度，以及这种差异是否在所有动物身上都是相同的，特别是那些用于研究的动物。这意味着有几个重要的问题仍未得到解答：首先，研究中用来理解晕动病的数学模型是否使用了适当的数字？第二，站姿的不同是否与你平时移动的速度是快还是慢，或者是两条腿还是四条腿有关？或者，这主要是因为眼睛在头骨中的位置不同：例如，猫的眼睛向前看和兔子的眼睛侧向看的排列是一样的吗？为了回答这些和其他问题，我建议对100只死亡哺乳动物的头部进行成像，并测量每对眼睛肌肉和相应的半规管在平面上的差异。将对20到40只恒河猴和兔子进行检查，以确定物种间的差异。剩下的40-60个样本将被抽样，以代表广泛的大小、身体运动类型和头骨形状。我建议用磁共振成像仪(MRI)对哺乳动物进行成像。这将使我能够观察头部，而不会造成身体上的损伤。这些平面的差异与身体大小、身体运动模式和头骨结构的关联将通过一套名为几何形态计量学的复杂数学工具进行评估。

Fix your eyes on a distant object and walk towards it. As you walk, your eyeballs constantly move around to compensate for the movements of your head. The structures responsible for monitoring head movement and feeding this information to the muscles of the eyeball are the semicircular canals of the inner ear. There are three of these half-moon shaped canals, one for each rotation of the head (e.g. tip up-down, rotate left-right and tilt left-right). These supply information via the brain to three pairs of muscles that can move the eyeball in the opposite direction to that of the head (e.g. tip down-up, rotate right-left and tilt right-left). Both the canals and muscles pairs are critical to the lives of all vertebrates. Without rapid communication between the canals and the muscle pairs, the compensatory movements of the eyes would lag behind movements of the head during motion, the image on the eye's retina would blur, and you would soon feel dizzy and eventually fall over. These are the severely debilitating symptoms experienced by patients with conditions like Meniere's disease. Clearly the eye muscles must move quickly to counteract movements of the head sensed by the canals. You might therefore imagine that the plane through each pair of muscles is aligned with the plane of the semicircular canal providing the primary input (e.g. up-down canal lies parallel to the muscle pair that moves the eye down-up). That way the signal output would closely match the direction of action required (e.g. a computer cursor is most easily moved up and down by moving the mouse up and down rather than side to side or diagonally). Such close spatial matching of signal and action would minimize the need for time-consuming readjustments of the signal by the brain. Because an aligned arrangement would seem to be the simplest and most logical, people have assumed that the planes are indeed parallel, or near to parallel. Over decades this assumption has gradually gained in credence, even appearing in some textbooks and as the basis for mathematical models of inner ear and eye muscle function. However, it turns out that there is evidence, albeit very limited, to suggest that the planes are not parallel and that the brain must therefore do some processing of the signal arising from the canals. The problem is that because the eye muscles and canals are not generally accessible to physical inspection, the available data is too little to ascertain the extent of the difference between the planes and whether such differences are the same in all animals, particularly those used in research. This means several important questions remain unanswered: First and foremost, are the mathematical models used in research to understand, for example, motion sickness employing the appropriate numbers? Second, is the difference in orientation connected to whether you normally move around rapidly or slowly, or on two or four legs? Or, is it primarily due to differences in the position of the eyes within the skull: for example is the arrangement the same in cats where the eyes face forward as it is in rabbits where the eyes face sideways. To answer these and other questions I propose imaging the heads of 100 dead mammals and measuring the difference in the plane of each pair of eye muscles and the corresponding semicircular canal. Twenty to forty rhesus monkeys and rabbits will be examined to determine variations within species. The remaining 40-60 specimens will be sampled to represent a wide range of sizes, types of body movement and skull shapes. I propose imaging the mammals with a magnetic resonance imager (MRI). This will enable me to look into the head without physically damaging it. Associations of the divergence of the planes with body size, mode of body movement and skull architecture will be evaluated with a set of complex mathematical tools called geometric morphometrics.