Functional Anatomy of Perceptual and Attentional Systems in the Primate Brain

由于视觉系统的处理能力有限，一个典型的场景包含许多不同的对象，这些对象竞争神经表征。在神经水平上，多个物体之间的竞争通过它们的视觉诱发反应的相互抑制来证明。多个对象之间的竞争可能会受到自下而上的感觉驱动机制（外源性注意）（如刺激显著性）和自上而下的目标导向影响（如选择性内源性注意）的影响。虽然多个物体之间的竞争最终在视觉皮层内解决，但自上而下的偏置信号的来源可能来自额叶和顶叶皮层的分布式网络。 我们以前曾报道过，前额叶皮层（PFC）病变的猴子在他们的自上而下的控制切换能力受损。然后，我们询问这些猴子是否会由于PFC的注意反馈源被剥夺而改变视觉皮层的单单位反应。我们预测，在PFC缺失的情况下，注意对视觉皮层V4区神经元反应和同步性的影响（神经元记录的位置）大大减少，注意力的剩余效果在时间上延迟，相反，在没有PFC的情况下，更多的错误;分心物捕获注意力，影响V4反应。然而，由于PFC损伤并没有消除V4中注意力的影响，因此在PFC之外必须存在其他自上而下的注意力控制信号。 以往的研究表明，右额中回（rMFG）可能作为一个节点的神经网络之间的相互作用，自上而下的目标导向的内源性注意和自下而上的，刺激驱动的外源性注意。我们测试了这一假设，通过比较的性能与rMFG切除术（以消除脑肿瘤）和健康对照组的患者的定向辨别任务。在内源性注意力试验中，一个有效的中央线索预测与90%的准确性的位置的阈值附近的伽柏补丁。在10%无效的试验中，Gabor贴片出现在与提示相反的位置。在外源性注意力试验中，一个线索出现短暂的两个外围位置之一，随后，在一个可变的刺激间间隔（ISI;范围0至700毫秒），由伽柏补丁在相同的（有效）或相反的位置（无效）。行为数据的分析表明，对于患者和对照组，有效的线索促进更快的反应时间相比，无效的线索，内源性和短期ISI外源性试验。然而，在较长的ISI外源性试验中，患者无法抑制他的反应，导致与对照组相比性能降低。这可能与患者在外源性线索的影响消失后无法以自上而下的方式重新定位注意力有关，并表明rMFG在外源性和内源性注意力模式之间切换的假定作用。静息状态功能磁共振成像（rsfMRI）的分析表明，在患者中，相对于对照组，两个大脑区域（右上级顶叶和右眶额皮质），通常连接到切除区域显着增加了他们的耦合在左半球的同源领域。因此，在没有右MFG的情况下，左半球同源物似乎通过增加与视觉空间、决策和脉冲控制电路的其他节点的通信来进行补偿（在肿瘤生长期间或切除后）。 我们还在健康参与者中进行了研究，以探索注意力的正常化模型，该模型提出注意力可以通过对比度或反应增益变化来影响表现，这取决于刺激大小和注意力场的相对大小。在这里，我们操纵的注意领域的情感效价（积极与消极的面孔），而刺激大小固定在一个空间线索任务。情绪化的面孔是吸引空间注意力的线索，然后是一对光栅。受试者在两个光栅中的一个上执行方向辨别任务;对于五个对比中的每一个（两个光栅的对比在任何给定的试验中是相同的，并且以随机顺序在试验中共同变化）。一个响应线索在刺激偏移指示的目标位置，产生有效的线索（情绪脸匹配响应线索）和无效的线索（不匹配）的条件。比较有效和无效试验的表现准确度（d '），揭示了每个对比的空间线索效应。每个情感效价（积极和消极）和每个试验条件（有效和无效）的心理测量功能与标准Naka-Rushton方程拟合。两个参数d 'max（高对比度水平下的渐近性能）和c50（对比度产生一半最大性能）分别确定响应增益和对比度增益。我们观察到的空间线索效应的变化与积极的面孔的对比度增益和消极的面孔的反应增益的变化一致。值得注意的是，积极和消极面孔的自我报告情绪强度的个体差异分别与对比度和反应增益的变化相关。功能性磁共振成像实验证实了被试对积极面孔的注意域比对消极面孔的注意域更宽。有效连接分析表明，情绪效价依赖的AF与背外侧前额叶皮层（DLPFC）对V1的反馈密切相关。总之，这些研究结果表明，情绪注意通过正常化框架塑造感知，DLPFC在这一过程中起着至关重要的作用。

A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple objects is evidenced by the mutual suppression of their visually evoked responses. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms (exogenous attention), such as stimulus salience, and top-down, goal-directed influences, such as selective, endogenous attention. Although the competition among multiple objects for representation is ultimately resolved within visual cortex, the source of top-down biasing signals likely derives from a distributed network of areas in frontal and parietal cortex. We previously reported that monkeys with lesions of prefrontal cortex (PFC) are impaired in their ability to switch top-down control. We then asked whether these same monkeys would have altered single-unit responses in visual cortex as a result of a deprived source of attentional feedback from PFC. We predicted that, in the absence of PFC, attentional effects on neuronal responses and synchrony in area V4 of visual cortex (the site of the neuronal recordings) were substantially reduced and the remaining effects of attention were delayed in time, indicating a critical role for PFC. Conversely, in the absence of PFC, many more errors were made; distracters captured attention and influenced V4 responses. However, because PFC lesions did not eliminate the effects of attention in V4, other sources of top-down attentional control signals to visual cortex must exist outside of PFC. Previous research has suggested that the right middle frontal gyrus (rMFG) may serve as a node of interaction between neural networks for top-down goal-directed endogenous attention and bottom-up, stimulus-driven exogenous attention. We tested this hypothesis by comparing the performance on an orientation discrimination task of a patient with a rMFG resection (to remove a brain tumor) and healthy controls. On endogenous attention trials, a valid central cue predicted with 90% accuracy the location of a peri-threshold Gabor patch. On the 10% invalid trials, the Gabor patch appeared in the opposite location to the cue. On exogenous attention trials, a cue appeared briefly at one of two peripheral locations, followed, after a variable inter-stimulus interval (ISI; range 0 to 700 ms), by a Gabor patch in either the same (valid) or opposite location (invalid). Analysis of behavioral data showed that for both patient and controls, valid cues facilitated faster reaction times compared to invalid cues, on endogenous and short ISI exogenous trials. However, at longer ISI exogenous trials, the patient was unable to withhold his responses, resulting in reduced performance compared to controls. This may be related to the patients inability to reorient attention in a top-down fashion after the effect of the exogenous cue has dissipated, and suggests a putative role of the rMFG in switching between exogenous and endogenous modes of attention. Analysis of resting state functional magnetic resonance imaging (rsfMRI) showed that in the patient, relative to controls, two brain regions (right superior parietal lobule and right orbitofrontal cortex) that are normally connected to the resected area significantly increased their coupling with the areas homologue in the left hemisphere. Thus, in the absence of the right MFG, the left hemisphere homologue appears to have compensated (either during tumor growth or after resection) by increasing communication with other nodes of the visuospatial, decision-making and impulse control circuitry. We have also undertaken studies in healthy participants to explore the normalization model of attention, which proposes that attention can affect performance by contrast or response gain changes, depending on the stimulus size and the relative size of the attention field. Here, we manipulated the attention field by affective valence (positive versus negative faces), while the stimulus size fixed in a spatial cueing task. Emotional faces served as a cue to attract spatial attention, followed by a pair of gratings. Subjects performed an orientation discrimination task on one of two gratings; for each of five contrasts (the contrasts of both gratings were identical on any given trial and co-varied across trials in random order). A response-cue at stimuli offset indicated the target location, yielding valid cues (the emotional face matched response-cue) and invalid cues (mismatched) conditions. Comparing performance accuracy (d') for valid and invalid trials revealed the spatial cueing effect for each contrast. The measured psychometric function for each affective valence (positive and negative) and each trial condition (valid and invalid) was fit with the standard Naka-Rushton equation. Two parameters d'max (asymptotic performance at high contrast levels) and c50 (the contrast yielding half maximum performance) determined response gain and contrast gain, respectively. We observed a change in the spatial cueing effect consonant with a change in contrast gain for positive faces and a change in response gain for negative faces. Significantly, individual differences in self-reported emotional strength of positive and negative faces correlated with contrast and response gain changes, respectively. A functional magnetic resonance imaging experiment confirmed that subjects attention fields were wider for positive faces than that for negative faces. Effective connectivity analysis showed that the emotional valence-dependent AF was closely associated with feedback from dorsolateral prefrontal cortex (DLPFC) to V1. Together, these findings suggest that emotional attention shapes perception by means of the normalization framework and that the DLPFC plays a crucial role in this process.