Top-down control of visual attention

Abstract

Top-down visual attention improves perception of selected stimuli and that improvement is reflected in the neural activity at many stages throughout the visual system. Recent studies of top-down attention have elaborated on the signatures of its effects within visual cortex and have begun identifying its causal basis. Evidence from these studies suggests that the correlates of spatial attention exhibited by neurons within the visual system originate from a distributed network of structures involved in the programming of saccadic eye movements. We summarize this evidence and discuss its relationship to the neural mechanisms of spatial working memory.

Figure 1

Summary of recent findings from studies comparing the timing of attention effects in different cortical areas. Each row represents a separate study. “” indicates shorter time difference compared to “” for the same study.

Figure 2

Possible routes for attentional signals from frontal and parietal areas (FEF and LIP) to an exemplar visual area (V4). Top, cytoarchitecture of area V4 and laminar patterns of afferent (left) and efferent (right) connections. Corticocortical feedback projections (from FEF, LIP, IT) synapse in superficial and deep layers [55, 58]. Specific pulvinar projections synapse primarily in deep layer 3 [83] while nonspecific pulvinar projections synapse in Layer 1 [61]. Feedforward input from visual areas such as V1 and V2 synapses primarily in Layer 4 [84]. Layer 2/3 neurons project to higher cortical areas such as IT [85], Layer 5 neurons project to subcortical structures such as the SC [86] and striatum [87], and Layer 6 neurons project to earlier cortical areas such as V1 and V2 [88] as well as to the pulvinar thalamus [61]. Bottom, selected projections forming paths from FEF and/or LIP to V4. These routes include: direct projections from LIP and FEF to V4 [55, 58, 59]; indirect projections through higher cortical areas such as IT [59, 88]; through SC and pulvinar thalamus [89]; through SC and lower visual areas including LGN, V1, and V2 [90]; or through BF cholinergic nuclei [91]. Abbreviations: FEF, Frontal Eye Field; LIP, Lateral Intraparietal area; IT, inferotemporal cortex; SC, superior colliculus; LGN, lateral geniculate nucleus; Pulv., pulvinar nucleus of the thalamus; BF, basal forebrain nuclei.