Ghasia Fatema F, Meng Hui, Angelaki Dora E
Department of Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Neurosci. 2008 May 7;28(19):5082-7. doi: 10.1523/JNEUROSCI.0513-08.2008.
Inverse and forward dynamic models have been conceptually important in computational motor control. In particular, inverse models are thought to convert desired action into appropriate motor commands. In parallel, forward models predict the consequences of the motor command on behavior by constructing an efference copy of the actual movement. Despite theoretical appeal, their neural representation has remained elusive. Here, we provide evidence supporting the notion that a group of premotor neurons called burst-tonic (BT) cells represent the output of the inverse model for eye movements. We show that BT neurons, like extraocular motoneurons but different from the evoked eye movement, do not carry signals appropriate for the half-angle rule of ocular kinematics during smooth-pursuit eye movements from eccentric positions. Along with findings of identical response dynamics as motoneurons, these results strongly suggest that BT cells carry a replica of the motor command. In contrast, eye-head (EH) neurons, a premotor cell type that is the target of Purkinje cell inhibition from the cerebellar flocculus/ventral paraflocculus, exhibit properties that could be consistent with the half-angle rule. Therefore, EH cells may be functionally related to the output of a forward internal model thought to construct an efference copy of the actual eye movement.
逆向和正向动力学模型在计算运动控制中具有重要的概念意义。特别是，逆向模型被认为能将期望的动作转换为适当的运动指令。与此同时，正向模型通过构建实际运动的传出副本，预测运动指令对行为的影响。尽管在理论上颇具吸引力，但其神经表征一直难以捉摸。在此，我们提供证据支持这样一种观点，即一组被称为爆发 - 紧张型（BT）细胞的运动前神经元代表了眼球运动逆向模型的输出。我们发现，BT神经元与眼外运动神经元一样，但与诱发的眼球运动不同，在从偏心位置进行的平稳跟踪眼球运动过程中，它们并不携带适合眼球运动学半角规则的信号。连同与运动神经元相同的反应动力学研究结果，这些结果有力地表明，BT细胞携带运动指令的副本。相比之下，眼 - 头（EH）神经元是一种运动前细胞类型，是小脑绒球/腹侧旁绒球浦肯野细胞抑制的靶点，其表现出的特性可能与半角规则一致。因此，EH细胞可能在功能上与一个正向内部模型的输出相关，该模型被认为能构建实际眼球运动的传出副本。
