Sommer Marc A, Wurtz Robert H
Department of Neuroscience, the Center for the Neural Basis of Cognition, and the Center for Neuroscience at the University of Pittsburgh, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Nature. 2006 Nov 16;444(7117):374-7. doi: 10.1038/nature05279. Epub 2006 Nov 8.
Each of our movements activates our own sensory receptors, and therefore keeping track of self-movement is a necessary part of analysing sensory input. One way in which the brain keeps track of self-movement is by monitoring an internal copy, or corollary discharge, of motor commands. This concept could explain why we perceive a stable visual world despite our frequent quick, or saccadic, eye movements: corollary discharge about each saccade would permit the visual system to ignore saccade-induced visual changes. The critical missing link has been the connection between corollary discharge and visual processing. Here we show that such a link is formed by a corollary discharge from the thalamus that targets the frontal cortex. In the thalamus, neurons in the mediodorsal nucleus relay a corollary discharge of saccades from the midbrain superior colliculus to the cortical frontal eye field. In the frontal eye field, neurons use corollary discharge to shift their visual receptive fields spatially before saccades. We tested the hypothesis that these two components-a pathway for corollary discharge and neurons with shifting receptive fields-form a circuit in which the corollary discharge drives the shift. First we showed that the known spatial and temporal properties of the corollary discharge predict the dynamic changes in spatial visual processing of cortical neurons when saccades are made. Then we moved from this correlation to causation by isolating single cortical neurons and showing that their spatial visual processing is impaired when corollary discharge from the thalamus is interrupted. Thus the visual processing of frontal neurons is spatiotemporally matched with, and functionally dependent on, corollary discharge input from the thalamus. These experiments establish the first link between corollary discharge and visual processing, delineate a brain circuit that is well suited for mediating visual stability, and provide a framework for studying corollary discharge in other sensory systems.
我们的每一个动作都会激活自身的感觉受体，因此追踪自身运动是分析感觉输入的必要组成部分。大脑追踪自身运动的一种方式是监测运动指令的内部副本，即伴随放电。这一概念可以解释为什么尽管我们频繁进行快速的眼球跳动（即扫视），我们仍能感知到一个稳定的视觉世界：关于每次扫视的伴随放电会使视觉系统忽略扫视引起的视觉变化。关键的缺失环节一直是伴随放电与视觉处理之间的联系。在这里，我们表明这种联系是由丘脑发出的靶向额叶皮质的伴随放电形成的。在丘脑中，背内侧核的神经元将来自中脑上丘的扫视伴随放电中继到皮质额叶眼区。在额叶眼区，神经元利用伴随放电在扫视之前在空间上移动其视觉感受野。我们测试了这样一个假设，即这两个成分——伴随放电通路和具有移动感受野的神经元——形成了一个回路，其中伴随放电驱动这种移动。首先，我们表明，已知的伴随放电的时空特性预测了进行扫视时皮质神经元空间视觉处理的动态变化。然后，我们通过分离单个皮质神经元从这种相关性转向因果关系，并表明当丘脑的伴随放电被中断时，它们的空间视觉处理会受损。因此，额叶神经元的视觉处理在时空上与来自丘脑的伴随放电输入相匹配，并且在功能上依赖于该输入。这些实验建立了伴随放电与视觉处理之间的第一个联系，描绘了一个非常适合介导视觉稳定性的脑回路，并为研究其他感觉系统中的伴随放电提供了一个框架。
