fMRI Research Laboratory, Columbia University Medical Center, New York, NY 10032, USA.
Brain Connect. 2012;2(3):164-75. doi: 10.1089/brain.2012.0072. Epub 2012 Jul 20.
Although expectation- and attention-related interactions between ventral and medial prefrontal cortex and stimulus category-selective visual regions have been identified during visual detection and discrimination, it is not known if similar neural mechanisms apply to other tasks such as visual search. The current work tested the hypothesis that high-level frontal regions, previously implicated in expectation and visual imagery of object categories, interact with visual regions associated with object recognition during visual search. Using functional magnetic resonance imaging, subjects searched for a specific object that varied in size and location within a complex natural scene. A model-free, spatial-independent component analysis isolated multiple task-related components, one of which included visual cortex, as well as a cluster within ventromedial prefrontal cortex (vmPFC), consistent with the engagement of both top-down and bottom-up processes. Analyses of psychophysiological interactions showed increased functional connectivity between vmPFC and object-sensitive lateral occipital cortex (LOC), and results from dynamic causal modeling and Bayesian Model Selection suggested bidirectional connections between vmPFC and LOC that were positively modulated by the task. Using image-guided diffusion-tensor imaging, functionally seeded, probabilistic white-matter tracts between vmPFC and LOC, which presumably underlie this effective interconnectivity, were also observed. These connectivity findings extend previous models of visual search processes to include specific frontal-occipital neuronal interactions during a natural and complex search task.
尽管在视觉检测和辨别过程中已经确定了腹侧和内侧前额叶皮层与刺激类别选择性视觉区域之间的期望和注意相关的相互作用，但尚不清楚类似的神经机制是否适用于其他任务，例如视觉搜索。当前的工作检验了一个假设，即先前涉及对象类别期望和视觉意象的高级额叶区域在视觉搜索期间与与对象识别相关的视觉区域相互作用。使用功能磁共振成像，受试者在复杂的自然场景中搜索特定的大小和位置变化的物体。一种无模型、空间独立的成分分析分离出多个与任务相关的成分，其中一个成分包括视觉皮层，以及腹侧前扣带皮层（vmPFC）内的一个簇，这与自上而下和自下而上的过程的参与一致。心理生理交互作用的分析显示 vmPFC 和对象敏感的外侧枕叶皮层（LOC）之间的功能连接增加，并且来自动态因果建模和贝叶斯模型选择的结果表明 vmPFC 和 LOC 之间存在双向连接，该连接被任务正向调节。使用图像引导的扩散张量成像，在 vmPFC 和 LOC 之间观察到功能种子、概率性的白质束，这些束可能是这种有效连接的基础。这些连通性发现将先前的视觉搜索过程模型扩展到包括在自然和复杂搜索任务期间特定的额-枕神经元相互作用。
