Department of Neurobiology and
Department of Neurobiology and.
J Neurosci. 2019 Mar 13;39(11):2114-2124. doi: 10.1523/JNEUROSCI.1767-18.2018. Epub 2019 Jan 15.
When searching a visual scene for a target, we tend not to look at items or locations we have already searched. It is thought that this behavior is driven by an inhibitory tagging mechanism that inhibits responses on priority maps to the relevant items. We hypothesized that this inhibitory tagging signal should be represented as an elevated response in neurons that keep track of stimuli that have been fixated. We recorded from 231 neurons in the frontal eye field (FEF) of 2 male animals performing a visual foraging task, in which they had to find a reward linked to one of five identical targets (Ts) among five distractors. We identified 38 neurons with activity that was significantly greater when the stimulus in the receptive field had been fixated previously in the trial than when it had not been fixated. The response to a fixated object began before the saccade ended, suggesting that this information is remapped. Unlike most FEF neurons, the activity in these cells was not suppressed during active fixation, had minimal motor responses, and did not change through the trial. Yet using traditional classifications from a memory-guided saccade, they were indistinguishable from the rest of the FEF population. We propose that these neurons keep track of any items that have been fixated within the trial and this signal is propagated by remapping. These neurons could be the source of the inhibitory tagging signal to parietal cortex, where a neuronal instantiation of inhibitory tagging is seen. When we search a scene for an item, we rarely examine the same location twice. It is thought that this is due to a neural mechanism that keeps track of the items at which we have looked. Here we identified a subset of neurons in the frontal eye field that preferentially responded to items that had been fixated earlier in the trial. These responses were remapped, appearing before the saccade even ended, and were not suppressed during maintained fixation. We propose that these neurons keep track of which items have been examined in search and could be the source of feedback that creates the inhibitory tagging seen in parietal cortex.
当我们在视觉场景中搜索目标时，我们往往不会看已经搜索过的项目或位置。人们认为这种行为是由一种抑制性标记机制驱动的，该机制会抑制优先映射到相关项目的反应。我们假设这种抑制性标记信号应该表现为跟踪已注视刺激的神经元中的响应升高。我们记录了 2 只雄性动物在执行视觉觅食任务时的 231 个额眼区（FEF）神经元的活动，在该任务中，它们必须在 5 个干扰物中找到与 5 个相同目标之一相关联的奖励。我们确定了 38 个神经元，当视野中的刺激在前一次试验中被注视过而不是未被注视时，其活动显著增加。对注视物体的反应在扫视结束之前开始，表明该信息被重新映射。与大多数 FEF 神经元不同，这些细胞的活动在主动注视期间不会被抑制，其运动反应最小，并且在整个试验过程中不会改变。然而，使用来自记忆引导扫视的传统分类，它们与 FEF 群体的其余部分无法区分。我们提出，这些神经元跟踪在试验期间被注视的任何项目，并且该信号通过重新映射来传播。这些神经元可能是抑制性标记信号传递到顶叶皮层的来源，在顶叶皮层中可以看到抑制性标记的神经元实例。当我们在场景中搜索项目时，我们很少两次检查同一位置。人们认为这是由于一种神经机制，它可以跟踪我们已经看过的项目。在这里，我们在额眼区识别出了一组神经元，它们优先对在试验早期被注视的项目做出反应。这些反应被重新映射，甚至在扫视结束之前出现，并且在维持注视期间不受抑制。我们提出，这些神经元跟踪在搜索中已检查过的项目，并且可能是产生在顶叶皮层中看到的抑制性标记的反馈的来源。
