Zupan L H, Peterka R J, Merfeld D M
Jenks Vestibular Physiology Laboratory, Massachusetts Eye and Ear Infirmary, Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts 02114, USA.
J Neurophysiol. 2000 Oct;84(4):2001-15. doi: 10.1152/jn.2000.84.4.2001.
Sensory systems often provide ambiguous information. Integration of various sensory cues is required for the CNS to resolve sensory ambiguity and elicit appropriate responses. The vestibular system includes two types of sensors: the semicircular canals, which measure head rotation, and the otolith organs, which measure gravito-inertial force (GIF), the sum of gravitational force and inertial force due to linear acceleration. According to Einstein's equivalence principle, gravitational force is indistinguishable from inertial force due to linear acceleration. As a consequence, otolith measurements must be supplemented with other sensory information for the CNS to distinguish tilt from translation. The GIF resolution hypothesis states that the CNS estimates gravity and linear acceleration, so that the difference between estimates of gravity and linear acceleration matches the measured GIF. Both otolith and semicircular canal cues influence this estimation of gravity and linear acceleration. The GIF resolution hypothesis predicts that inaccurate estimates of both gravity and linear acceleration can occur due to central interactions of sensory cues. The existence of specific patterns of vestibuloocular reflexes (VOR) related to these inaccurate estimates can be used to test the GIF resolution hypothesis. To investigate this hypothesis, we measured eye movements during two different protocols. In one experiment, eight subjects were rotated at a constant velocity about an earth-vertical axis and then tilted 90 degrees in darkness to one of eight different evenly spaced final orientations, a so-called "dumping" protocol. Three speeds (200, 100, and 50 degrees /s) and two directions, clockwise (CW) and counterclockwise (CCW), of rotation were tested. In another experiment, four subjects were rotated at a constant velocity (200 degrees /s, CW and CCW) about an earth-horizontal axis and stopped in two different final orientations (nose-up and nose-down), a so-called "barbecue" protocol. The GIF resolution hypothesis predicts that post-rotatory horizontal VOR eye movements for both protocols should include an "induced" VOR component, compensatory to an interaural estimate of linear acceleration, even though no true interaural linear acceleration is present. The GIF resolution hypothesis accurately predicted VOR and induced VOR dependence on rotation direction, rotation speed, and head orientation. Alternative hypotheses stating that frequency segregation may discriminate tilt from translation or that the post-rotatory VOR time constant is dependent on head orientation with respect to the GIF direction did not predict the observed VOR for either experimental protocol.
感觉系统常常提供模糊的信息。中枢神经系统（CNS）需要整合各种感觉线索来解决感觉模糊并引发适当的反应。前庭系统包括两种类型的传感器：测量头部旋转的半规管，以及测量重力惯性力（GIF）的耳石器官，重力惯性力是重力和线性加速度引起的惯性力之和。根据爱因斯坦的等效原理，重力与线性加速度引起的惯性力无法区分。因此，中枢神经系统必须用其他感觉信息来补充耳石测量，以便区分倾斜和平移。重力惯性力分辨率假说指出，中枢神经系统估计重力和线性加速度，使得重力估计值和线性加速度估计值之间的差异与测量到的重力惯性力相匹配。耳石和半规管线索都会影响对重力和线性加速度的这种估计。重力惯性力分辨率假说预测，由于感觉线索的中枢相互作用，可能会出现重力和线性加速度的不准确估计。与这些不准确估计相关的特定前庭眼反射（VOR）模式的存在可用于检验重力惯性力分辨率假说。为了研究这个假说，我们在两种不同的实验方案中测量了眼球运动。在一个实验中，八名受试者绕地球垂直轴以恒定速度旋转，然后在黑暗中倾斜90度至八个不同的均匀间隔的最终方向之一，这是一种所谓的“倾倒”方案。测试了三种速度（200、100和50度/秒）以及顺时针（CW）和逆时针（CCW）两种旋转方向。在另一个实验中，四名受试者绕地球水平轴以恒定速度（200度/秒，CW和CCW）旋转，并停在两个不同的最终方向（鼻朝上和鼻朝下），这是一种所谓的“烧烤”方案。重力惯性力分辨率假说预测，两种方案的旋转后水平前庭眼反射眼球运动都应包括一个“诱导”前庭眼反射成分，该成分可补偿线性加速度的耳间估计值，即使不存在真正的耳间线性加速度。重力惯性力分辨率假说准确地预测了前庭眼反射和诱导前庭眼反射对旋转方向、旋转速度和头部方向的依赖性。其他假说认为频率分离可区分倾斜和平移，或者旋转后前庭眼反射时间常数取决于头部相对于重力惯性力方向的方向，但这两种假说都无法预测任一实验方案中观察到的前庭眼反射。
