Kumar Arun N, Han Yanning H, Liao Ke, Rucker Janet C, Ramat Stefano, Leigh R J
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106-1702, USA.
Ann N Y Acad Sci. 2005 Apr;1039:404-16. doi: 10.1196/annals.1325.038.
Clinicians conventionally test saccades at the bedside by noting the accuracy, initiation time, and speed of large movements, with the patient's head stationary. Partly for methodological reasons, laboratory analysis of saccades has mainly focused on movements of 20 degrees or less. By measuring the velocity waveform of large saccades, it is possible to examine more closely the way in which brain stem and cerebellum guide the eye to the target. Large saccades made by healthy humans show a positively skewed velocity profile. Slow saccades made by patients with brain-stem disorders show a prolonged plateau of low velocity. Some patients with cerebellar disorders may show increased acceleration and deceleration of saccades. Each of these velocity waveforms can be modeled by changing the parameters that describe medium-lead burst neuron firing. In certain other brain-stem and cerebellar disorders, transient decelerations or premature terminations of saccades occur; such velocity waveforms cannot be modeled solely by changing the parameters that describe burst neuron firing. Instead, it is necessary to postulate dysfunction of the mechanism that normally inhibits pontine omnipause neurons, thereby permitting burst neurons to discharge until the saccade is completed. Analysis of large, abnormal saccades calls for application of novel techniques to identify the beginning and end of the saccadic pulse command.
临床医生通常在患者头部固定的情况下，通过观察大幅度眼球运动的准确性、起始时间和速度，在床边对扫视进行测试。部分由于方法学原因，实验室对扫视的分析主要集中在20度或更小角度的运动上。通过测量大幅度扫视的速度波形，可以更仔细地研究脑干和小脑引导眼睛看向目标的方式。健康人做出的大幅度扫视显示出正偏态的速度曲线。脑干疾病患者做出的缓慢扫视显示出低速的延长平台期。一些小脑疾病患者可能表现出扫视的加速和减速增加。通过改变描述中导爆发神经元放电的参数，可以对这些速度波形中的每一种进行建模。在某些其他脑干和小脑疾病中，会出现扫视的短暂减速或过早终止；这种速度波形不能仅通过改变描述爆发神经元放电的参数来建模。相反，有必要假设正常情况下抑制脑桥全暂停神经元的机制存在功能障碍，从而允许爆发神经元放电直至扫视完成。对大幅度异常扫视的分析需要应用新技术来识别扫视脉冲指令的开始和结束。
