Martin Anne B, von der Heydt Rüdiger
Department of Neuroscience, the Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, and
Department of Neuroscience, the Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, and The Zanvyl Krieger Mind/Brain Institute, the Johns Hopkins University, Baltimore, Maryland 21218.
J Neurosci. 2015 Apr 29;35(17):6860-70. doi: 10.1523/JNEUROSCI.3590-14.2015.
Neurons at early stages of the visual cortex signal elemental features, such as pieces of contour, but how these signals are organized into perceptual objects is unclear. Theories have proposed that spiking synchrony between these neurons encodes how features are grouped (binding-by-synchrony), but recent studies did not find the predicted increase in synchrony with binding. Here we propose that features are grouped to "proto-objects" by intrinsic feedback circuits that enhance the responses of the participating feature neurons. This hypothesis predicts synchrony exclusively between feature neurons that receive feedback from the same grouping circuit. We recorded from neurons in macaque visual cortex and used border-ownership selectivity, an intrinsic property of the neurons, to infer whether or not two neurons are part of the same grouping circuit. We found that binding produced synchrony between same-circuit neurons, but not between other pairs of neurons, as predicted by the grouping hypothesis. In a selective attention task, synchrony emerged with ignored as well as attended objects, and higher synchrony was associated with faster behavioral responses, as would be expected from early grouping mechanisms that provide the structure for object-based processing. Thus, synchrony could be produced by automatic activation of intrinsic grouping circuits. However, the binding-related elevation of synchrony was weak compared with its random fluctuations, arguing against synchrony as a code for binding. In contrast, feedback grouping circuits encode binding by modulating the response strength of related feature neurons. Thus, our results suggest a novel coding mechanism that might underlie the proto-objects of perception.
视觉皮层早期阶段的神经元会发出诸如轮廓片段等基本特征的信号，但这些信号是如何组织成可感知对象的尚不清楚。理论提出，这些神经元之间的尖峰同步编码了特征的分组方式（同步绑定），但最近的研究并未发现同步性会随着绑定而如预期那样增加。在这里，我们提出特征通过增强参与特征神经元反应的内在反馈回路被分组为“原对象”。这一假设预测，同步性仅存在于从同一分组回路接收反馈的特征神经元之间。我们记录了猕猴视觉皮层中的神经元，并利用神经元的一种内在特性——边界所有权选择性，来推断两个神经元是否属于同一分组回路。我们发现，正如分组假设所预测的那样，绑定在同回路神经元之间产生了同步性，但在其他神经元对之间则没有。在一项选择性注意任务中，同步性在被忽视的对象以及被关注的对象中都出现了，并且更高的同步性与更快的行为反应相关，这正如早期分组机制所预期的那样，该机制为基于对象的处理提供了结构。因此，同步性可能是由内在分组回路的自动激活产生的。然而，与随机波动相比，与绑定相关的同步性提升较弱，这与同步性作为绑定编码的观点相悖。相比之下，反馈分组回路通过调节相关特征神经元的反应强度来编码绑定。因此，我们的结果表明了一种可能是感知原对象基础的新型编码机制。
