MODELING THE ROLE OF THE CEREBELLAR FASTIGIAL NUCLEI IN PRODUCING ACCURATE SACCADES - THE IMPORTANCE OF BURST TIMING
MODELING THE ROLE OF THE CEREBELLAR FASTIGIAL NUCLEI IN PRODUCING ACCURATE SACCADES - THE IMPORTANCE OF BURST TIMING
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DOI：
10.1016/0306-4522(95)00239-f
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发表时间：
1995-10-01
期刊：
影响因子：
3.3
通讯作者：
DEAN, P
中科院分区：
文献类型：
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作者：
DEAN, P
临床和实验数据表明，小脑蚓部的损伤会导致扫视准确性的永久丧失。因此，扫视产生的模型需要为小脑提供一个角色。已经提出，蚓部响应于关于预期扫视的幅度的信息来调整扫视内部反馈回路的增益。小脑顶核（通过其引导蚓输出）如何影响脑干扫视回路以实现这种效果的模型分三个阶段构建。(1)脑干由罗宾逊的内部反馈模型的一个版本表示，该模型将兴奋性爆发神经元放电与水平扫视动力学联系起来。(2)最初的模型被损伤以模拟顶核的双侧失活的影响，即缓慢的高测量扫视。这需要减少内部反馈通路的突触重量，并降低兴奋性爆发神经元的增益。由此产生的脑干模型作为一个准备测试的影响，神经元放电模式内的小脑顶核。(3)这些放电模式是用最近的电生理学研究中的测量结果模拟的。研究发现，如果从反馈信号中减去来自对侧小脑顶核神经元的模拟爆发，则在模型中可以恢复扫视准确性和正常动力学（即添加到命令信号）在扫视早期，而同侧小脑顶核神经元的爆发则在眼跳的后期被加入到反馈信号中。这种模式对应于所观察到的神经元爆发的时间在小脑顶核，并占定性的影响，单方面的刺激和失活的小脑顶核和小脑vermis.This产生准确的扫视的方法也有助于时间的最佳控制，通过增加扫视的加速和减速。顶核爆发开始和持续时间的适当时机对于这些作用是必不可少的。关于小脑损伤对身体其他部位快速运动的影响的证据表明，小脑可能使用类似的策略来控制广泛的简单运动。
Clinical and experimental data indicate that damage to the cerebellar vermis results in permanent loss of saccadic accuracy. Models of saccade production therefore need to provide a role for the cerebellum. It has been proposed that the vermis adjusts the gain of the saccadic internal feedback loop in response to information about the amplitude of the intended saccade. A model of how the fastigial nuclei (through which vermal output is channelled) influence brainstem saccadic circuitry to achieve this effect was constructed in three stages. (1) The brainstem was represented by a version of Robinson's internal feedback model, which relates excitatory burst neuron discharge to horizontal saccade dynamics. (2) The original model was lesioned to simulate the effects of bilateral inactivation of the fastigial nuclei, namely slow hypermetric saccades. This required reducing the synaptic weight of the internal feedback pathway, and lowering the gain of the excitatory burst neurons. The resultant brainstem-only model served as a preparation for testing the effects of neuronal discharge patterns within the fastigial nuclei. (3) These discharge patterns were simulated using measurements from recent electrophysiological studies.It was found that saccadic accuracy and normal dynamics were restored in the model if the simulated burst from neurons in the contralateral fastigial nucleus were subtracted from the feedback signal(i.e. added to the command signal) early in the saccade, and the burst from neurons in the ipsilateral fastigial nucleus were added to the feedback signal later in the saccade. This pattern corresponds to the observed timing of neuronal bursts in the fastigial nuclei, and accounts qualitatively for the effects of unilateral stimulation and inactivation of both the fastigial nuclei and the cerebellar vermis.This method of producing accurate saccades also contributes to time optimal control, by increasing both saccadic acceleration and deceleration. Appropriate timing of burst onset and duration in the fastigial nuclei is essential for these roles. Evidence concerning the effects of cerebellar damage on fast movements of other parts of the body suggests that the cerebellum may use similar strategies for controlling a wide range of simple movements.