Berman Rebecca A, Cavanaugh James, McAlonan Kerry, Wurtz Robert H
Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland
Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
J Neurophysiol. 2017 Apr 1;117(4):1720-1735. doi: 10.1152/jn.00679.2016. Epub 2016 Dec 21.
Saccades should cause us to see a blur as the eyes sweep across a visual scene. Specific brain mechanisms prevent this by producing suppression during saccades. Neuronal correlates of such suppression were first established in the visual superficial layers of the superior colliculus (SC) and subsequently have been observed in cortical visual areas, including the middle temporal visual area (MT). In this study, we investigated suppression in a recently identified circuit linking visual SC (SCs) to MT through the inferior pulvinar (PI). We examined responses to visual stimuli presented just before saccades to reveal a neuronal correlate of suppression driven by a copy of the saccade command, referred to as a corollary discharge. We found that visual responses were similarly suppressed in SCs, PI, and MT. Within each region, suppression of visual responses occurred with saccades into both visual hemifields, but only in the contralateral hemifield did this suppression consistently begin before the saccade (~100 ms). The consistency of the signal along the circuit led us to hypothesize that the suppression in MT was influenced by input from the SC. We tested this hypothesis in one monkey by inactivating neurons within the SC and found evidence that suppression in MT depends on corollary discharge signals from motor SC (SCi). Combining these results with recent findings in rodents, we propose a complete circuit originating with corollary discharge signals in SCi that produces suppression in visual SCs, PI, and ultimately, MT cortex. A fundamental puzzle in visual neuroscience is that we frequently make rapid eye movements (saccades) but seldom perceive the visual blur accompanying each movement. We investigated neuronal correlates of this saccadic suppression by recording from and perturbing a recently identified circuit from brainstem to cortex. We found suppression at each stage, with evidence that it was driven by an internally generated signal. We conclude that this circuit contributes to neuronal suppression of visual signals during eye movements.
扫视动作本应让我们在眼睛扫过视觉场景时看到模糊的影像。特定的脑机制通过在扫视过程中产生抑制作用来防止这种情况发生。这种抑制作用的神经元相关物最初是在上丘（SC）的视觉表层中发现的，随后在包括颞中视觉区（MT）在内的皮层视觉区域中也观察到了。在本研究中，我们调查了一个最近发现的通过下枕叶（PI）将视觉上丘（SCs）与MT连接起来的神经回路中的抑制作用。我们检查了在扫视动作之前呈现的视觉刺激的反应，以揭示由扫视命令副本驱动的抑制作用的神经元相关物，即所谓的伴随放电。我们发现，SCs、PI和MT中的视觉反应都受到了类似的抑制。在每个区域内，向两个视觉半视野的扫视都会抑制视觉反应，但只有在对侧半视野中，这种抑制作用才会在扫视之前（约100毫秒）持续开始。该神经回路中信号的一致性使我们推测，MT中的抑制作用受到了来自SCs的输入的影响。我们通过使一只猴子的SCs内的神经元失活来检验这一假设，并发现有证据表明MT中的抑制作用依赖于来自运动SCs（SCi）的伴随放电信号。将这些结果与最近在啮齿动物中的发现相结合，我们提出了一个完整的神经回路，该回路起源于SCi中的伴随放电信号，在视觉SCs、PI以及最终的MT皮层中产生抑制作用。视觉神经科学中的一个基本难题是，我们经常进行快速的眼球运动（扫视），但很少察觉到每次运动伴随的视觉模糊。我们通过记录并扰动一个最近发现的从脑干到皮层的神经回路，研究了这种扫视抑制的神经元相关物。我们在每个阶段都发现了抑制作用，并有证据表明它是由一个内部产生的信号驱动的。我们得出结论，这个神经回路有助于在眼球运动期间对视觉信号进行神经元抑制。
