Department of Biological Structure, University of Washington, Washington National Primate Research Center, Seattle, Washington.
Department of Psychology, University of Washington, Seattle, Washington.
J Neurophysiol. 2020 Jun 1;123(6):2311-2325. doi: 10.1152/jn.00586.2019. Epub 2020 May 13.
In the primate visual cortex, both the magnitude of the neuronal response and its timing can carry important information about the visual world, but studies typically focus only on response magnitude. Here, we examine the onset and offset latency of the responses of neurons in area V4 of awake, behaving macaques across several experiments in the context of a variety of stimuli and task paradigms. Our results highlight distinct contributions of stimuli and tasks to V4 response latency. We found that response onset latencies are shorter than typically cited (median = 75.5 ms), supporting a role for V4 neurons in rapid object and scene recognition functions. Moreover, onset latencies are longer for smaller stimuli and stimulus outlines, consistent with the hypothesis that longer latencies are associated with higher spatial frequency content. Strikingly, we found that onset latencies showed no significant dependence on stimulus occlusion, unlike in inferotemporal cortex, nor on task demands. Across the V4 population, onset latencies had a broad distribution, reflecting the diversity of feedforward, recurrent, and feedback connections that inform the responses of individual neurons. Response offset latencies, on the other hand, displayed the opposite tendency in their relationship to stimulus and task attributes: they are less influenced by stimulus appearance but are shorter in guided saccade tasks compared with fixation tasks. The observation that response latency is influenced by stimulus- and task-associated factors emphasizes a need to examine response timing alongside firing rate in determining the functional role of area V4. Onset and offset timing of neuronal responses can provide information about visual environment and neuron's role in visual processing and its anatomical connectivity. In the first comprehensive examination of onset and offset latencies in the intermediate visual cortical area V4, we find neurons respond faster than previously reported, making them ideally suited to contribute to rapid object and scene recognition. While response onset reflects stimulus characteristics, timing of response offset is influenced more by behavioral task.
在灵长类动物视觉皮层中，神经元反应的幅度和时间都可以携带有关视觉世界的重要信息，但研究通常只关注反应幅度。在这里，我们在各种刺激和任务范式的背景下，在几个实验中检查了清醒、行为灵长类动物 V4 区神经元反应的起始和结束潜伏期。我们的结果突出了刺激和任务对 V4 反应潜伏期的不同贡献。我们发现反应起始潜伏期比通常引用的要短（中位数=75.5 毫秒），支持 V4 神经元在快速物体和场景识别功能中的作用。此外，较小的刺激和刺激轮廓的起始潜伏期较长，这与较长的潜伏期与较高的空间频率内容相关的假设一致。引人注目的是，我们发现与颞下皮质不同，V4 中的起始潜伏期与刺激遮挡或任务需求无关。在整个 V4 群体中，起始潜伏期具有广泛的分布，反映了告知单个神经元反应的前馈、递归和反馈连接的多样性。相比之下，响应的结束潜伏期与刺激和任务属性的关系呈现相反的趋势：它们受刺激出现的影响较小，但在引导性眼球运动任务中比在固定任务中更短。观察到反应潜伏期受刺激和任务相关因素的影响，强调在确定 V4 区域的功能作用时，需要与发放率一起检查反应时间。神经元反应的起始和结束时间可以提供有关视觉环境以及神经元在视觉处理及其解剖连接中的作用的信息。在对中间视觉皮层 V4 中的起始和结束潜伏期进行的首次全面检查中，我们发现神经元的反应速度比以前报道的要快，这使它们非常适合快速物体和场景识别。虽然反应起始反映了刺激特征，但反应结束的时间更多地受到行为任务的影响。
