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，多种刺激之间的竞争表现为视觉诱发反应的相互抑制。 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。虽然表征刺激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，我们问是否猴子与后顶叶皮层（PPC）的病变会表现出类似或不同的行为影响。 我们的研究结果表明，与PFC病变的猴子不同，PPC病变的猴子在切换自上而下控制的能力方面没有选择性受损。相反，它们在空间定位它们需要区分的目标方面具有选择性损害。 因此，PFC在改变任务需求的基础上切换注意力控制的能力中起着至关重要的作用，而PPC在将注意力资源分配到行为相关的空间位置中起着至关重要的作用。 另一个主要目标是通过测试关于注意力分散是否来自增加的感官驱动干扰或低效的自上而下控制的假设，更好地表征ADHD中注意力分散的性质。我们采用了一个注意过滤范式，其中的歧视难度和分心物显着性参数操纵。 增加辨别困难应该会增加自上而下过程的负荷，而增加干扰物的显著性应该会导致更强的感官干扰。 我们发现了一个显着的相互作用的歧视困难和分心物的显着性：对于困难的歧视，ADHD儿童过滤干扰一样有效的健康儿童和成年人，所有群体都慢于响应高与低显着性分心物。 相比之下，对于简单的区分，ADHD儿童比健康儿童和成人慢得多，犯的错误也更多。 对于容易的歧视，健康的儿童和成年人过滤出高显着性干扰一样容易低显着性干扰，但ADHD儿童的反应慢，对试验与低显着性干扰比试验与高显着性干扰。事实上，ADHD儿童表现出有效的注意力过滤时，任务要求高，但显示不足和非典型的干扰过滤低任务要求下，表明过滤机制保持完好，在这些儿童，但触发激活注意力是选择性受损。 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。 内源性注意力试验，一个有效的中央线索预测的位置的阈值附近的伽柏补丁的准确率为90%。 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，线索出现短暂的两个外围位置之一，其次，经过可变的刺激间间隔（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，导致与对照组相比表现降低。 这可能与患者无法重新定位注意力在一个自上而下的方式后，外源性线索的影响已经消散，并建议一个假定的作用，rMFG外源性和内源性模式之间的切换注意。我们正在继续检验这一假设。

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 stimuli 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 stimuli 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 monkeys with lesions of posterior parietal cortex (PPC) would show similar or different behavioral effects. Our results showed that, unlike monkeys with PFC lesions, those with PPC lesions are not selectively impaired in their ability to switch top-down control. Rather, they have a selective impairment in spatially locating targets they are required to discriminate. Thus, the PFC plays a critical role in the ability to switch attentional control on the basis of changing task demands, whereas the PPC plays a critical role in allocating attentional resources to behaviorally relevant spatial locations. Another major goal has been to better characterize the nature of distractibility in ADHD by testing hypotheses about whether distractibility arises from increased sensory-driven interference or from inefficient top-down control. We employed an attentional filtering paradigm in which discrimination difficulty and distractor salience were parametrically manipulated. Increased discrimination difficulty should add to the load of top-down processes, whereas increased distractor salience should result in stronger sensory interference. We found a striking interaction of discrimination difficulty and distractor salience: For difficult discriminations, ADHD children filtered distractors as efficiently as healthy children and adults, and all groups were slower to respond with high vs. low salience distractors. In contrast, for easy discriminations, ADHD children were much slower and made more errors than healthy children and adults. For easy discriminations, healthy children and adults filtered out high salience distractors as easily as low salience distractors, but ADHD children were slower to respond on trials with low salience distractors than on trials with high salience distractors. The fact that ADHD children exhibit efficient attentional filtering when task demands are high, but show deficient and atypical distractor filtering under low task demands suggests that filtering mechanisms remain intact in these children but the trigger for activating attention is selectively impaired. 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 perithreshold 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 interstimulus 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 patient's 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. We are continuing to test this hypothesis.