Kunimatsu Jun, Tanaka Masaki
Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.
Brain Nerve. 2011 Aug;63(8):871-7.
Although the roles of the thalamocortical pathways in somatic movements are well documented, their roles in eye movements have only recently been examined. The oculomotor-related areas in the frontal cortex receive inputs from the basal ganglia and the cerebellum via the thalamus. Consistent with this, neurons in the paralaminar part of the ventrolateral (VL), ventroanterior (VA), and mediodorsal (MD) nuclei and those in the intralaminar nuclei exhibit a variety of eye movement-related responses. To date, the thalamocortical pathways are known to play at least 2 roles in eye movements. First, they are involved in the generation of volitional, but not reactive, saccades. Thalamic neurons discharge during anti-saccades, which are known to be impaired in several neurological and psychiatric disorders, such as Parkinson's disease, attention deficit/hyperactivity disorder, and schizophrenia. In addition, neurons in the thalamus also exhibit a gradual increase in firing rate that predicts the timing of self-initiated saccades. Recent inactivation experiments have established the causal roles of these thalamic signals in the generation of volitional saccades. Second, the thalamocortical pathways transmit the efference copy signals for eye movements. During inactivation of the MD thalamus, which relays signals from the superior colliculus to the frontal eye field (FEF), the accuracy of the saccade is reduced in tasks requiring efference copy signals. In addition, inactivation of the same pathways reduces the predictive visual response associated with saccades in neurons in the FEF. Moreover the VL thalamus has been reported to play a role in monitoring smooth pursuit. While the functional analysis of thalamocortical pathways in eye movements is just a beginning, the anatomical data suggest their important roles. Analysis of eye movement control may shed light on the functions of the thalamocortical pathways in general, and may reveal the neural mechanisms of cerebro-cerebellar, cerebro-basal ganglia, and cerebro-thalamic interactions.
虽然丘脑皮质通路在躯体运动中的作用已有充分记载，但它们在眼球运动中的作用直到最近才得到研究。额叶皮质中与眼球运动相关的区域通过丘脑接收来自基底神经节和小脑的输入。与此一致的是，腹外侧（VL）、腹前（VA）和背内侧（MD）核的旁层部分以及板内核中的神经元表现出各种与眼球运动相关的反应。迄今为止，已知丘脑皮质通路在眼球运动中至少发挥两种作用。首先，它们参与自主性扫视运动的产生，但不参与反射性扫视运动。丘脑神经元在反扫视运动期间放电，已知在几种神经和精神疾病中，如帕金森病、注意力缺陷多动障碍和精神分裂症，反扫视运动会受到损害。此外，丘脑中的神经元在自发起的扫视运动的时间预测上也表现出发射率的逐渐增加。最近的失活实验证实了这些丘脑信号在自主性扫视运动产生中的因果作用。其次，丘脑皮质通路传递眼球运动的传出副本信号。在中继上丘到额叶眼区（FEF）信号的MD丘脑失活期间，在需要传出副本信号的任务中，扫视运动的准确性会降低。此外，相同通路的失活会降低FEF中神经元与扫视运动相关的预测性视觉反应。此外，据报道，VL丘脑在监测平稳跟踪中发挥作用。虽然对眼球运动中丘脑皮质通路的功能分析才刚刚开始，但解剖学数据表明了它们的重要作用。对眼球运动控制的分析可能有助于揭示丘脑皮质通路的总体功能，并可能揭示脑-小脑、脑-基底神经节和脑-丘脑相互作用的神经机制。
