Chen Chih-Yang, Hafed Ziad M
Werner Reichardt Centre for Integrative Neuroscience, Tuebingen University, Tuebingen, Germany.
Graduate School of Neural and Behavioural Sciences, International Max Planck Research School, Tuebingen University, Tuebingen, Germany; and.
J Neurophysiol. 2017 Apr 1;117(4):1657-1673. doi: 10.1152/jn.00911.2016. Epub 2017 Jan 18.
Saccades cause rapid retinal-image shifts that go perceptually unnoticed several times per second. The mechanisms for saccadic suppression have been controversial, in part because of sparse understanding of neural substrates. In this study we uncovered an unexpectedly specific neural locus for spatial frequency-specific saccadic suppression in the superior colliculus (SC). We first developed a sensitive behavioral measure of suppression in two macaque monkeys, demonstrating selectivity to low spatial frequencies similar to that observed in earlier behavioral studies. We then investigated visual responses in either purely visual SC neurons or anatomically deeper visual motor neurons, which are also involved in saccade generation commands. Surprisingly, visual motor neurons showed the strongest visual suppression, and the suppression was dependent on spatial frequency, as in behavior. Most importantly, suppression selectivity for spatial frequency in visual motor neurons was highly predictive of behavioral suppression effects in each individual animal, with our recorded population explaining up to ~74% of behavioral variance even on completely different experimental sessions. Visual SC neurons had mild suppression, which was unselective for spatial frequency and thus only explained up to ~48% of behavioral variance. In terms of spatial frequency-specific saccadic suppression, our results run contrary to predictions that may be associated with a hypothesized SC saccadic suppression mechanism, in which a motor command in the visual motor and motor neurons is first relayed to the more superficial purely visual neurons, to suppress them and to then potentially be fed back to cortex. Instead, an extraretinal modulatory signal mediating spatial-frequency-specific suppression may already be established in visual motor neurons. Saccades, which repeatedly realign the line of sight, introduce spurious signals in retinal images that normally go unnoticed. In part, this happens because of perisaccadic suppression of visual sensitivity, which is known to depend on spatial frequency. We discovered that a specific subtype of superior colliculus (SC) neurons demonstrates spatial-frequency-dependent suppression. Curiously, it is the neurons that help mediate the saccadic command itself that exhibit such suppression, and not the purely visual ones.
扫视会导致视网膜图像快速移动，这种移动每秒会在感知上被忽略几次。扫视抑制的机制一直存在争议，部分原因是对神经基质的了解不足。在这项研究中，我们在上丘（SC）中发现了一个出乎意料的特定神经位点，用于空间频率特异性扫视抑制。我们首先在两只猕猴身上开发了一种敏感的抑制行为测量方法，证明了对低空间频率的选择性，这与早期行为研究中观察到的情况相似。然后，我们研究了纯视觉SC神经元或解剖学上更深层的视觉运动神经元的视觉反应，这些神经元也参与扫视生成指令。令人惊讶的是，视觉运动神经元表现出最强的视觉抑制，并且这种抑制依赖于空间频率，就像在行为中一样。最重要的是，视觉运动神经元对空间频率的抑制选择性在很大程度上预测了每只动物的行为抑制效果，我们记录的群体即使在完全不同的实验环节中也能解释高达约74%的行为方差。视觉SC神经元的抑制作用较弱，对空间频率没有选择性，因此只能解释高达约48%的行为方差。就空间频率特异性扫视抑制而言，我们的结果与可能与假设的SC扫视抑制机制相关的预测相反，在该机制中，视觉运动和运动神经元中的运动指令首先传递到更浅层的纯视觉神经元，以抑制它们，然后可能反馈到皮层。相反，在视觉运动神经元中可能已经建立了介导空间频率特异性抑制的视网膜外调节信号。扫视会反复重新调整视线，在视网膜图像中引入通常未被注意到的虚假信号。部分原因是扫视期间视觉敏感性的抑制，已知这种抑制依赖于空间频率。我们发现上丘（SC）神经元的一种特定亚型表现出空间频率依赖性抑制。奇怪的是，表现出这种抑制的是那些有助于介导扫视指令本身的神经元，而不是纯视觉神经元。
