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

盯着远处的物体，朝它走去。当你走路的时候，你的眼球会不断地移动来补偿你头部的运动。内耳的半规管是负责监控头部运动并将信息传递给眼球肌肉的结构。有三个半月形的运河，每旋转一次头部就有一个运河（例如，指尖上下，左右旋转和左右倾斜）。这些眼球通过大脑向三对肌肉提供信息，这些肌肉可以使眼球朝着与头部相反的方向运动（例如向下、向左左右旋转和向左左右倾斜）。椎管和肌肉对所有脊椎动物的生命都至关重要。如果没有神经管和肌肉对之间的快速沟通，眼睛的代偿运动就会落后于头部的运动，眼睛视网膜上的图像就会模糊，你很快就会感到头晕，最终摔倒。这些是患有梅尼埃氏病等疾病的患者所经历的严重衰弱症状。很明显，眼部肌肉必须快速运动，以抵消脑管感知到的头部运动。因此，你可能会想象，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，上下管平行于使眼睛上下运动的肌肉对）。这样，信号输出将与所需的操作方向紧密匹配（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，最容易上下移动）。这种信号和动作在空间上的紧密匹配将使大脑重新调整信号所需的时间最小化。因为对齐的排列似乎是最简单和最合乎逻辑的，所以人们假设这些平面确实是平行的，或者接近平行的。几十年来，这一假设逐渐得到了人们的信任，甚至出现在一些教科书中，并作为内耳和眼肌功能的数学模型的基础。然而，有证据表明，尽管非常有限，但这些平面并不是平行的，因此大脑必须对来自运河的信号进行一些处理。问题在于，由于眼部肌肉和眼管通常无法进行物理检查，现有的数据太少，无法确定这些平面之间的差异程度，也无法确定这些差异是否在所有动物身上都一样，尤其是在研究中使用的动物身上。这意味着有几个重要的问题仍未得到解答：首先，研究中用于理解晕车的数学模型是否采用了合适的数字？第二，方向的不同是否与你通常是用两条腿还是四条腿快速移动或缓慢移动有关？或者，这主要是由于眼睛在头骨内的位置不同：例如，猫的眼睛朝前的排列和兔子的眼睛朝侧的排列是一样的吗？为了回答这些问题和其他问题，我建议对100只死去的哺乳动物的头部进行成像，并测量每对眼肌的平面和相应的半规管的差异。将对20到40只恒河猴和兔子进行检查，以确定物种内的变异。剩下的40-60个标本将被采样，以代表广泛的尺寸，身体运动类型和头骨形状。我建议用核磁共振成像仪（MRI）对哺乳动物进行成像。这样我就能在不损伤头部的情况下观察到它的内部。平面发散与身体大小、身体运动模式和头骨结构的关联将通过一套称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.