Mechanisms of top-down attention

Attention exhibits characteristic neural signatures in brain regions that process sensory signals. An important area of future research is to understand the nature of top-down signals that facilitate attentional guidance towards behaviorally relevant locations and features. In this review, we discuss recent studies that have made progress towards understanding: (i) the brain structures and circuits involved in attentional allocation; (ii) top-down attention pathways, particularly as elucidated by microstimulation and lesion studies; (iii) top-down modulatory influences involving subcortical structures and reward systems; (iv) plausible substrates and embodiments of top-down signals; and (v) information processing and theoretical constraints that might be helpful in guiding future experiments. Understanding top-down attention is crucial for elucidating the mechanisms by which we can filter sensory information to pay attention to the most behaviorally relevant events. Attention exhibits characteristic neural signatures in brain regions that process sensory signals. An important area of future research is to understand the nature of top-down signals that facilitate attentional guidance towards behaviorally relevant locations and features. In this review, we discuss recent studies that have made progress towards understanding: (i) the brain structures and circuits involved in attentional allocation; (ii) top-down attention pathways, particularly as elucidated by microstimulation and lesion studies; (iii) top-down modulatory influences involving subcortical structures and reward systems; (iv) plausible substrates and embodiments of top-down signals; and (v) information processing and theoretical constraints that might be helpful in guiding future experiments. Understanding top-down attention is crucial for elucidating the mechanisms by which we can filter sensory information to pay attention to the most behaviorally relevant events. influence on the nervous system due to extrinsic properties of the stimuli. search task in which a subject is required to find a target item among several distractors, and the target is defined by a unique conjunction of features. In this type of search task, locating the target is more difficult because distractors share some of the features of the target and thus the target does not obviously stand or pop out. attention paid to a subset of the sensory inputs through mental focusing. first epoch of neural activity that travels from lower to higher visual areas on the onset of a visual stimulus via feed-forward connections. attentional process that influences sensory processing in an automatic and persistent manner. attention paid through orienting of sensory organs toward a sensory input of interest. mental impression of an external stimulus. search task in which a subject is required to find a target item among several distractors, and the target is defined by a unique visual feature not shared with any of the distractors. The target thus stands or pops out and is easy to find. map of visual space constructed from a combination of properties of the external stimuli, and intrinsic expectations, knowledge and current behavioral goals. second epoch of neural activity that occurs after an initial response to onset of a stimulus and is mediated by intra-cortical horizontal connections and inter-cortical feedback connections. map of stimulus conspicuity over visual space. in search tasks, a set-size effect is observed if the time required to find the target depends on the total number of items in the display (the set size). map of behaviorally relevant locations over visual space. influence on the nervous system due to extra-retinal effects such as intrinsic expectations, knowledge and goals. attentional process that exerts influence on sensory processing through an act of volition, such as willfully shifting attention to the right part of space.